Di- and polysaccharides. - PowerPoint PPT Presentation


Title: Di- and polysaccharides.


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Lecture ? 15
  • Di- and polysaccharides.
  • Terpenes.

Ass. Medvid I.I. Ass. Burmas N.I
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Outline
  • Oligosaccharides.
  • The following functions of carbohydrates in
    humans.
  • 3.Classification of disaccharides
  • maltose
  • cellobiose
  • lactose
  • saccharose.
  • 4. Polysaccharides (glucanes).
  • a) Homopolysaccharides
  • - Structure, composition and properties of
    cellulose.
  • - Structure, composition and properties of
    starch.
  • - Glycogen, dextranes, inuline, pectin compounds,
    chitin.
  • b) Heteropolysaccharides.
  • 5. Glycoconjugates.

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  • 6. Lipids.
  • 7. Chemical properties of fats
  • 8. Phospholipids. Waxes.
  • 9. Nonsaponifiable lipids.
  • 10. Terpenes and terpenoids. Terpene
    biosynthesis.
  • 11. Classification of terpenes.
  • 12. Carotenoids.
  • 13. Steroids.
  • 14. Properties of cholesterol. Biosynthesis of
    cholesterol.
  • 15. Vitamins.
  • 16. Water-soluble vitamins.
  • 17.Water insoluble (lipid-soluble) vitamins.

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  • Oligosaccharides.
  • The term oligosaccharide is often used for
    carbohydrates that consist of between two and ten
    monosaccharide units. Oligosaccharides are
    carbohydrates that contain from two to ten
    monosaccharide units.
  • Disaccharides are the most common type of
    oligosaccharide. Disaccharides are carbohydrates
    composed of two monosaccharide units covalently
    bonded to each other. Like monosaccharides,
    disaccharides are crystalline, water-soluble
    substances. Saccharose (table sugar) and lactose
    (milk sugar) are disaccharides. Within the human
    body, oligosaccharides are often found associated
    with proteins and lipids in complexes that have
    both structural and regulatory functions. Free
    oligosaccharides, other than disaccharides, are
    seldom encountered in biological systems
  • Complete hydrolysis of an oligosaccharide
    produces monosaccharides. Upon hydrolysis, ?
    disaccharide produces two monosaccharides, ?
    trisaccharide three monosaccharides, ?
    hexasaccharide six monosaccharides, and so on.

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  • Carbohydrates are the most abundant class of
    bioorganic molecules on planet Earth. Although
    their abundance in the human body is relatively
    low, carbohydrates constitute about 75 by mass
    of dry plant materials.
  • Green (chlorophyll-containing) plants produce
    carbohydrates via photosynthesis. In this
    process, carbon dioxide from the air and water
    from the soil are the reactants, and sunlight
    absorbed by chlorophyll is the energy source.
  • Plants have two main uses for the carbohydrates
    they produce. In the form of cellulose,
    carbohydrates serve as structural elements, and
    in the form of starch, they provide energy
    reserves for the plants.
  • Dietary intake of plant materials is the major
    carbohydrate source for humans and animals. The
    average human diet should ideally be about
    two-thirds carbohydrate by mass.

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  • 2. The following functions of carbohydrates in
    humans.
  • Carbohydrates have the following functions in
    humans
  • 1. Carbohydrate oxidation provides energy
  • 2. Carbohydrate storage, in the form of glycogen,
    provides ? short- term energy reserve.
  • 3. Carbohydrates supply carbon atoms for the
    synthesis of other biochemical substances
    (proteins, lipids, and nucleic acids).
  • 4. Carbohydrates form part of the structural
    framework of DNA and RNA molecules.
  • 5. Carbohydrate "markers" on cell surfaces play
    key roles in cell -cell recognition processes.

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  • 3.Classification of disaccharides
  • (1) N?n-reducing disaccharides. In these
    disaccharides the two hexose units are linked
    together through their reducing (i ?. aldehydic
    or ketonic) groups which is , in aldoses
    and , in ketoses. Now in such cases since
    the reducing groups of both hexoses are lost, the
    resulting compound (disaccharide) will be
    non-reducing. Hence such disaccharides do not
    form osazone do not show mutarotation and do not
    react with reagents like Felings solution,
    Tollens reagent, etc. Important example of
    non-reducing disaccharides is saccharose.
  • (2) Reducing disaccharides. In these
    disaccharides, one hexose unit is linked through
    its reducing carbon to the non-reducing carbon
    (C4 or ?6) of the other Now since the reducing
    group of one of the hexoses is not involved, the
    resulting disaccharide will be ? reducing sugar.
    Maltose and lactose are examples of reducing
    disaccharides.

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  • As mentioned earlier, disaccharides are those
    sugars which on hydrolysis give two moles of
    monosaccharides general these are sweet-testing
    crystalline, water-soluble substances, easily
    hydrolysed by enzymes and dilute mineral acids.
    The common disaccharides have the general formula
    C12H22O11 which during hydrolysis take one
    molecule of water to form two hexoses.
  • Disaccharides are formed by intermolecular
    dehydration between two monosaccharide molecules,
    e.g. In the formation of disaccharides, at least
    one monosaccharide unit is linked to the other
    through the glycosidic carbon atom. In other
    words we can say that in the formation of
    disaccharide, reducing property of at least one
    hexose unit is lost. Hence disaccharides may be
    considered as glycosides in which both components
    of the molecules are sugars. Disaccharides may
    exist in two types, namely non-reducing and
    reducing depending on the fact that ?1 of one
    hexose is linked to the carbonyl carbon at other
    carbon atom of other hexose. Weak oxidizing
    agents, such as Tollens, Feling's, and Benedict's
    solutions, oxidize the carbonyl group end of ?
    monosaccharide to give an -onic acid.

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  • Disaccharides. ? monosaccharide that has cyclic
    forms (hemiacetal or hemiketal) can react with an
    alcoho1 to form ? glycoside (acetal or ketal).
    This same type of reaction can be used to produce
    ? disaccharide, ? carbohydrate in which two
    monosaccharides are bonded together. In
    disaccharide formation, one of the monosaccharide
    reactants functions as ? hemiacetal or hemiketal,
    and the other functions as an alcohol.
  • Monosaccharide monosaccharide disaccharide
    ?2O
  • The bond that links the two monosaccharides of ?
    disaccharide together is called ? glycosidic
    linkage. ? glycosidic linkage is the
    carbon-oxygen-carbon bond that joins the two
    components of ? glycoside together. The bond that
    links the two monosaccharides of ? disaccharide
    together is called ? glycosidic linkage. We now
    examine the structures and properties of four
    important disaccharides maltose, cellobiose,
    lactose, and saccharose. As we consider details
    of the structures of these compounds, we will
    find that the configuration (a or ß) at carbon-1
    of the reacting monosaccharides is often of prime
    importance.

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  • Maltose, often called malt sugar, is produced
    by breaking down the polysaccharide starch, as
    takes place in plants when seeds germinate and in
    human beings during starch digestion. It is ?
    common ingredient in baby foods and is found in
    malted milk. Malt (germinated barley that has
    been baked and ground) contains maltose hence
    the name malt sugar. Structurally, maltose is
    made up of two D-glucopyranose units, one of
    which must be ?-D-glucose. The formation of
    maltose from two glucose molecules is as follows
  • ?-D-Glucose ?-D-Glucose
    ?-(1-4)-linkage

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So, a-maltose can be named as 4-O-(a-D-glucopyrano
sido)-a-D-glucopyranose, ß-maltose
4-O-(a-D-glucopyranosido)-ß-D-glucopyranose.
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  • The glycosidic linkage between the two glucose
    units is called an ?(1 - 4) linkage. The two
    ??-groups that form the linkage are attached,
    respectively, to carbon-1 of the first glucose
    unit (in an a configuration) and to carbon-4 of
    the second. Maltose is ? reducing sugar, because
    the glucose unit on the right has ? hemiacetal
    carbon atom (?-1).Thus this glucose unit can open
    and close it is in equilibrium with its
    open-chain aldehyde form. This means there are
    actually three forms of the maltose molecule
    ?-maltose, ?-maltose, and the open-chain form. In
    the solid state, the ?-form is dominant. The most
    important chemical reaction of maltose is
    hydrolysis. Hydrolysis of D-maltose, whether in ?
    laboratory flask or in ? living organism,
    produces two molecules of D-glucose.

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  • Cellobiose is produced as an intermediate in
    the hydrolysis of the polysaccharide cellulose.
    Like maltose, cellobiose contains two D-glucose
    monosaccharide units. It differs from maltose in
    one of D-glucose units - the one functioning as ?
    hemiacetal - must have ? ?-configuration instead
    of the ? configuration of maltose. This change in
    configuration gives ? ?(1-4) glycosidic linkage.

?-D-Glucose
?(1-4)-linkage
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a-cellobiose can be named as 4-O-(ß-D-glucopyranos
ido)-a-D-glucopyranose, ß-cellobiose
4-O-(ß-D-glucopyranosido)-ß-D-glucopyranose.
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  • Like maltose, cellobiose is a reducing sugar,
    has three isomeric forms in aqueous solution, and
    upon hydrolysis produces two D-glucose molecules.
    Despite these similarities, maltose and
    cellobiose have different biological behaviors.
    These differences are related to the
    stereochemistry of their glycosidic linkages.
    Maltase, the enzyme that breaks the
    glucose-glucose ?(1-4) linkage present in
    maltose, is found both in the human body and in
    yeast. Consequently, maltose is digested easily
    by humans and is readily fermented by yeast. Both
    the human body and yeast lack the enzyme
    cellobiase needed to break the glucose - glucose
    ?(1-4) linkage of cellobiose. Thus cellobiose
    cannot be digested by humans or fermented by
    yeast. In maltose and cellobiose, the two units
    of the disaccharide are identical - two glucose
    units in each case.
  • Maltose and cellobiose have different
    arrangement in space. In maltose molecule
    a-glycosidic linkage has axial arrangement, in
    cellobiose molecule ß-glycosidic linkage
    equatorial. Its cases club-similar structure of
    amylose and linear structure of cellulose.

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  • Lactose includes ?-D-galactopyranose unit and ?
    D-glucopyranose unit joined by ?-(1-4) glycosidic
    linkage

?-D-galactose ?-D-Glucose
?(1-4)-linkage
The glucose hemiacetal center is active when
galactose bonds to glucose in the formation of
lactose, so lactose is ? reducing sugar (the
glucose ring can open to give an
aldehyde).Lactose is the major sugar found in
milk. This accounts for its common name, milk
sugar. Enzymes in animal mammary glands take
glucose from the bloodstream and synthesize
lactose in ? four-step process. Epimerization of
glucose yields galactose, and then the ?(1-4)
linkage forms between ? galactose and ? glucose
unit. Lactose is an important ingredient in
commercially produced infant formulas that are
designed to simulate mother' s milk. Souring of
milk is caused by the conversion of lactose to
lactic acid by bacteria in the milk.
Pasteurization of milk is ? quick-heating process
that kills most of the bacteria and retards the
souring process. Lactose can be hydrolyzed by
acid or by the enzyme lactase, forming an
equimolar mixture of galactose and glucose. In
the human body, the galactose produced in such
way is then converted to glucose by other
enzymes. The genetic condition lactose
intolerance, an inability of the human digestive
system to hydrolyze lactose.
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a-lactose can be named as 4-O-(ß-D-galactopyranosi
do)-a-D-glucopyranose, ß-lactose
4-O-(ß-D-galactopyranosido)-ß-D-glucopyranose. Arr
angement in space is similar to cellobiose
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  • Saccharose, common table sugar, is the most
    abundant of all disaccharides and occurs
    throughout the plant kingdom. It is produced
    commercially from the juice of sugar cane and
    sugar beets. Sugar cane contains up to 20 by
    mass saccharose, and sugar beets contain up to 17
    by mass saccharose. The two monosaccharide
    units present in ?-D-saccharose molecule are
    ?-D-glucose in form of ?-D-glucopyranose and
    ?-D-fructose in form of ?-D-fructofuranose. The
    glycosidic linkage is not ? (1-4) linkage, as was
    in case with maltose, cellobiose, and lactose. It
    is instead an ?,?(1 - 2) glycosidic linkage. The
    ??-group on carbon-2 of D-fructose (the hemiketal
    carbon) reacts with the ??-group on carbon-l of
    D-glucose (the hemiacetal carbon).

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Saccharose can be named as 2-O-(a-D-glucopyranosid
o)-ß-D-fructofuranose.
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  • Saccharose, unlike maltose, cellobiose, and
    lactose, is ? non-reducing sugar. No helmiacetal
    or hemiketal center is present in the molecule,
    because the glycosidic linkage involves the
    reducing ends of both monosaccharides.
    Saccharose, in the solid state and in solution,
    exists in only one form - there are no ? and ?
    isomers, and an open-chain form is not possible.
    Saccharase, the enzyme needed to break the ?,?(1
    - 2) linkage in saccharose, is present in the
    human body. Hence saccharose is an easily
    digested substance.

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  • Saccharose hydrolysis (digestion) produces an
    equimolar mixture of glucose and fructose called
    invert sugar. When saccharose is cooked with
    acid-containing foods such as fruits or berries,
    partial hydrolysis takes place, forming some
    invert sugar. Jams and jellies prepared in this
    manner are actually sweeter than the pure
    saccharose added to the original mixture, because
    one-to-one mixtures of glucose and fructose taste
    sweeter than saccharose.
  • Saccharose is dextrorotatory. On hydrolysis it
    gives one molecule of glucose and one molecule of
    fructose. Now since fructose is more strongly
    laevorotatory than the dextrorotatory property of
    glucose, the mixture (product) after hydrolysis
    will be laevorotatory. This reaction is also as
    inversion of sugar because the dextrorotatory
    case sugar is converted into laevorotatory
    product due to hydrolysis. The mixture of glucose
    and fructose is called invert sugar.

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dextrorotatory
laevorotatory
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  • 4. Polysaccharides (glucanes)
  • ? polysaccharides (glucanes) contains many
    monosaccharide units bonded to each other by
    glycosidic linkages. The number of monosaccharide
    units in polysaccharides varies from ? few
    hundred to hundreds of thousands. Polysaccharides
    are polymers. In some, the monosaccharides are
    bonded together in ? linear (unbranched) chain.
    In others, there is extensive branching of the
    chains. Unlike monosaccharides and most
    disaccharides, polysaccharides are not sweet and
    do not give positive reaction with Tollens,
    Benedicts, and Felings solutions. They have
    limited water solubility because of their size.
    However, the ??-groups present in molecule can
    individually become hydrated by water molecules.
    The result is usually ? thick colloidal
    suspension of the polysaccharide in water.
    Polysaccharides, such as flour and cornstarch,
    are often used as thickening agents in sauces,
    desserts, and gravy.

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Linear and branched structure of polysaccharides
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  • Although there are many naturally occurring
    polysaccharides, in this section we will focus on
    only four of them cellulose, starch, glycogen,
    and chitin. All play vital roles in living
    systems - cellulose and starch in plants,
    glycogen in humans and other animals, and chitin
    in arthropods.
  • Polysaccharides may be divided into two
    classes homopolysaccharides, which are composed
    of one type of monosaccharide units, and
    heteropolysaccharides, which contain two or more
    different types of monosaccharide units.
  • Starch, glycogen and cellulose are homoglycans
    as they are made of only glucose and are called
    glucanes or glucosanes. Homopolysaccharides which
    containe only pentoses called pentosanes, hexoses
    hexosanes. On the other hand,
    mucopolysaccharides like hyaluronic acid and
    chondroitine sulphate are heteroglycanes as they
    are made up of different monosaccharide units.
  • Common formula for pentosanes (C5H8O4)n, for
    hexosanes (C6H10O5)n.

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  • Homopolysaccharides
  • Structure, composition and properties of
    cellulose.
  • Cellulose is the most abundant polysaccharide.
    It is the structural component of the cell walls
    of plants. Approximately half of all the carbon
    atoms in the plant kingdom are contained in
    cellulose molecules. Structurally, cellulose is ?
    linear (unbranched) D-glucose polymer in which
    the glucose units are linked by ?(1-4) glycosidic
    bonds.

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  • At heating with mineral acids cellulose
    hydrolyzed by the following scheme

In cellulose glucopyranose remainders have linear
structure and hydrogen bonds
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  • Typically, cellulose chains contain about 5000
    glucose units, which gives macromolecules with
    molecular masses of about 900,000. Cotton is
    almost pure cellulose (95 ) and wood is about
    50 cellulose. Even though it is ? glucose
    polymer, cellulose is not ? source of nutrition
    for human beings. Humans lack the enzymes capable
    of catalyzing the hydrolysis of ? (1- 4) linkages
    in cellulose. Even grazing animals have the
    enzymes necessary for cellulose digestion.
    However, the intestinal tracts of animals such as
    horses, cows, and sheep contain bacteria that
    produce cellulose, an enzyme that can hydrolyze ?
    (1- 4) linkages and produce free glucose from
    cellulose. Thus grasses and other plant materials
    are ? source of nutrition for grazing animals.
    The intestinal tracts of termites contain the
    same microorganisms, which enable termites to use
    wood as their source of food. Microorganisms in
    the soil can also metabolize cellulose, which
    makes possible the biodegradation of dead plants.
    Despite its nondigestibility, cellulose is still
    an important component of ? balanced diet. It
    serves as dietary fiber. Dietary fiber provides
    the digestive tract with "bulk" that helps move
    food through the intestinal tract and facilitates
    the excretion of solid wastes. Cellulose readily
    absorbs water, leading to softer stools and
    frequent bowel action. Links have been found
    between the length of time stools spend in the
    colon and possible colon cancer.

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  • High-fiber food may also play ? role in weight
    control. Obesity is not seen in parts of the
    world where people eat large amounts of
    fiber-rich foods. Many of the weight-loss
    products on the market are composed of
    bulk-inducing fibers such as methylcellulose.
  • FIGURE. Cellulose microfibrils.
  • Some fibers bind lipids such as cholesterol and
    carry out them of the body with the feces. This
    lowers blood lipid concentrations and possibly
    the risk of heart and artery disease.

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  • Structure, composition and properties of
    starch.
  • Starch, like cellulose, is ? polysaccharide
    containing only glucose units. It is the storage
    polysaccharide in plants. If excess of glucose
    enters ? plant cell, it is converted to starch
    and stored for later use. When the cell cannot
    get enough glucose from outside, it hydrolyzes
    starch to release glucose. Iodine is often used
    to test the presence of starch in solution.
    Starch-containing solutions turn ? dark blue when
    iodine is added. As starch is broken down through
    acid or enzymatic hydrolysis to glucose monomers,
    the blue color disappears. Two different
    polyglucose polysaccharides can be isolated from
    most starches amylose and amylopectin. Amylose,
    ? straight-chain glucose polymer, usually
    accounts for 15 20 of the starch
    amylopectin, ? highly branched glucose polymer,
    accounts for the remaining 80 85 of the
    starch.

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  • In amylose's structure, the glucose units are
    connected by ?(1- 4) glycosidic linkages.

  • Starch (amylose)
  • The number of glucose units present in an
    amylose chain depends on the source of the
    starch 200 350 monomer units are usually
    present. Amylopectin, the other polysaccharide in
    starch, is similar to amylose, but has ? high
    degree branched structure in the polymer. ? one
    branch link containe 20-25 glucose units. The
    number of glucose units present in an amylopectin
    chain consists of 1000 and more units. The branch
    points involve ?(1 6) linkages

Starch (amylopectin)
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  • Because of the branching, amylopectin has ?
    larger average molecular mass than the linear
    amylose. The average molecular mass of amylose is
    40000 or more it is 1-6 mln. for amylopectin.
    Note that all of the glycosidic linkages in
    starch (both amylose and amylopectin) are of the
    ?-type. In amylose, they are all ?(1 - 4) in
    amylopectin, both ?(1 -4) and ?(1 -6) linkages
    are present. Because ? linkages can be broken
    through hydrolysis within the human digestive
    tract (with the help of the enzyme amylase),
    starch has nutritional value for humans. The
    starches present in potatoes and cereal grains
    (wheat, rice, corn, etc.) account for
    approximately two-thirds of the world' s food
    consumption.
  • Fermentayion hydrolysis of starch is shown below

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  • Glycogen, chitin.
  • Glycogen, like cellulose and starch, is ?
    polysaccharide containing only glucose units. It
    is the glucose storage polysaccharide in humans
    and animals. Its function is thus similar to that
    of starch in plants, and it is sometimes referred
    to as animal starch. Liver cells and muscle cells
    are the storage sites for glycogen in humans.
    Glycogen has ? structure similar to that of
    amylopectin all glycosidic linkages are of the
    ?-type, and both (1-4) and (1-6) linkages are
    present. Glycogen and amylopectin differ in the
    number of glucose units between branches and the
    total number of glucose units present in ?
    molecule. Glycogen is about three times more
    highly branched than amylopectin, and it is much
    larger, with ? molar mass. ? one branch link
    containe 8-12 glucose units, rare 2- 4. When
    excess of glucose is present in the blood
    (normally from eating too much starch), the liver
    and muscle tissue convert the excess of glucose
    to glycogen, which is then stored in these
    tissues. Whenever the glucose blood level drops
    (from exercise, fasting, or normal activities),
    some stored glycogen is hydrolyzed back to
    glucose. These two opposing processes are called
    glycogenesis and glycogenolysis, the formation
    and decomposition of glycogen, respectively.

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  • Glycogen is an ideal storage form for glucose.
    The large size of these macromolecules prevents
    them from diffusing out of cells. Also,
    conversion of glucose to glycogen reduces osmotic
    pressure. Cells would burst because of increased
    osmotic pressure if all of the glucose in
    glycogen were present in cells in free form. High
    concentrations of glycogen in ? cell sometimes
    cases precipitate or crystallize into glycogen
    granules. These granules are discernible in
    photographs of cells under electron microscope
    magnification. The glucose polymers amylose,
    amylopectin, and glycogen compare as follows in
    molecular size and degree of branching
  • Amylose Up to 1000 glucose units no branching
  • Amylopectin Up to 100,000 glucose units branch
    points every 20-25 glucose units
  • Glycogen Up to 1,000,000 glucose units branch
    points every 8-12 glucose units

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  • FIGURE. Structure of amylopectine (?), glycogen
    (b)

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Dextranes
  • Dextranes have bacterial origin, contain
    remainders of a-D-glucopyranose. Dextranes obtain
    from saccharose at the present of bacterium
    (Leuconostoc mesenteroides). The main type of
    bond is a-1,6-glycosidic bond, in place of
    branching a-1,4- and a-1,3-glycosidic bonds.
    The average molecular mass of dextranes is few
    millions. Partly hydrolyzed dextranes (m. m.
    40000-800000) use in pharmacy as plasmasubstitute
    (Polyglucin, Reopolyglucin).

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Inuline
  • Inuline reserve polysaccharide, present in
    plants. Inuline has linear structure and consists
    of remainders of ß-D-fructofuranose, joined by
    2,1-glycosidic bonds, in the end of inuline is
    a-D-glucopyranose remainder (like saccharose).
    Molecular mass of inuline is up to 6000. Use for
    obtaining of D-fructose.

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Pectin compounds
  • Pectin compounds (pectins) polysaccharides
    consist of polygalacturonic acid, which contain
    remainders of a-D-galacturonic acid joined by
    1,4-glycosidic bonds. Part of carboxyl grups
    present in appearance of methyl ether. Water
    solutions of pectins form stable gels. Pectins
    have antiulcer properties.

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  • Chitin is ? polysaccharide that is similar to
    cellulose in both function and structure. Its
    function is to give rigidity to the exoskeletons
    of crabs, lobsters, shrimp, insects, and other
    arthropods. It also occurs in the cell walls of
    fungi. Structurally, chitin is ? linear polymer
    (no branching) with all ?(1- 4) glycosidic
    linkages, as in cellulose. Chitin differs from
    cellulose in that the monosaccharide present is
    an N-acetylamino derivative of D-glucose.

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  • Heteropolysaccharides.
  • Unlike all the polysaccharides we have
    discussed up to this point, mucopolysaccharides
    are heteropolysaccharides rather than
    homopolysaccharides.
  • Mucopolysaccharides are compounds that occur in
    connective tissue associated with joints in
    animals and humans. Their function is primarily
    that of lubrication, ? necessary requirement if
    movement is to occur. The name mucopolysaccharide
    comes from the highly viscous, gelatinous
    (mucus-like) consistency of these substances in
    aqueous solution.
  • ? heteropolysaccharide is ? polysaccharide in
    which more than one (usually two) type of
    monosaccharide unit is present.
  • One of the most common mucopolysaccharides is
    hyaluronic acid, ? heteropolysaccharide in which
    the following two glucose derivatives alternate
    in the structure.

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  • It is ? highly viscous substance and has ?
    molecular weight in several hundred millions.
    Hyaluronic acid is ? principal component of the
    ground substance of connective tissue. Among
    other places it is found in skin, synovial fluid,
    vitreous hemour of the eye, and umbilical cord.
    It exercises ? cementing function in the tissues
    and capillary walls, and forms ? coating gel
    round the ovum. It accounts for about 80 of the
    viscosity of synovial fluid which contains about
    0. 02 0.05 of hyaluronate. Repeat part of
    hyaluronic acid is D-glucuronic acid and
    N-acetyl-D-glucosamine joined by ß-1,3-glycosidic
    bond, between disaccharide fragments ß-1,4.
    Molecular mass of hyaluronic acid is from 1600 to
    6400.
  • (1,4)-O-?-D-Glucopyranosyluronic
    acid-(1,3)-2-acetamino-2-dezoxy-?-D-glucopyranose.

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  • Hyaluronic acid is split up by the enzyme
    hyalurosidase into ? number of small molecule. If
    fluid containing this enzyme is injected into ?
    tissue it spreads rapidly, from the site of
    injection and thus this enzyme is sometimes
    referred as the spreading factor. It is found
    in relatively high concentration in the testis
    and seminal fluid, in the venoms of certain
    snakes and insects, and in some bacteria. The
    enzyme also has ? physiological role in
    fertilization. The sperm is rich in the enzyme
    and the former can thus advance better in the
    cervical canal and finally penetrates the ovum.

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  • Chondroitin sulfate. It has similar structure
    as hyaluronic acid with the difference that the
    N-acetyl-D-glucosamine unit of the molecule is
    replaced by N-acetyl-D-galactosamine unit with
    sulphate group. Repeat part of chondroitin
    sulphate is D-glucuronic acid and
    N-acetyl-D-galactosamine which contains sulfate
    group. Inside of disaccharide fragment is
    ß-1,3-glycosidic bond between fragments ß-1,4.
    Sulfate group forms ether bond with hydroxyl
    group of N-acetyl-D-galactosamine in location 4
    (chondroitin-4-sulfate) or in location 6
    (chondroitin-6-sulfate). Chondroitin sulfates are
    found in cartilage, bone, heart valves, tendons
    and cornea.
  • (1,4)-O-?-D-Glucopyranosyluronic
    acid-(1,3)-2-acetamino-2-dezoxy-6-O-sulfo-?-D-gala
    ctopyranose.

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Hydrocarbon chains of chondroitin-4-sulfate
contain up to 150 disaccharides remainders,
joined in organism by O-glycosidic bonds with
hydroxyl groups of aminoacid remainders.
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  • Dermatan sulfate. (Varying amounts of
    D-glucuronic acid may be present. Concentration
    increases during aging process.)
  • (1,4)-O-?-L-idopyranosyluronic acid-(1,3)-2-acetam
    ino-2-dezoxy-4-O-sulfo-?-D-galactopyranose.

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  • Heparin. It is naturally occurring
    anticoagulant found mainly in the liver, and also
    in lung, spleen, kidney and intestinal mucosa. It
    prevents blood clotting by inhibiting the
    prothrombin-thrombin conversion and thus
    eliminating the thrombin effect on fibrinogen.
    Repeat part of heparin consists of D-glucosamin
    and uronic acid, joined by a-1,4-glycosidic
    bonds. As uronic acid in heparin present
    L-iduronic acid or, very rare, D-glucuronic acid.
    Remainders of glucosamine and L-iduronic acid
    partly sulfonated. Molecular mass of heparin is
    16000-20000.

(1,4)-O-?-D-idupyranosyluronic acid-2-O-sulfo-(1,4
)-2-sulfamino-2-dezoxy-6-O-sulfo-?-D-glucopyranose
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  • 5. Glycoconjugates.
  • The compounds that result from the covalent
    linkages of carbohydrate molecules to both
    proteins and lipids are collectively known as the
    glycoconjugates. These substances have profound
    effects on the function of individual cells, as
    well as the cell-cell interactions of
    multicellular organisms. There are two classes of
    carbohydrate-protein conjugate proteoglycans and
    glycoproteins. Although both molecular types
    contain ???bohydrate and protein, their
    structures and functions appear, in general, to
    be substantially different. The glycolipids,
    which are oligosaccharide-containing lipid
    molecules, are found predominantly on the outer
    surface of plasma membranes.

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  • Proteoglycans are distinguished from the common
    glycoproteins by their extremely high
    carbohydrate content, which may constitute as
    much as 95 of the dry weight of such molecules.
    These molecules are found predominantly in the
    extracellular matrix (intercellular material) of
    tissues. All proteoglycans contain GAG chains.
    The GAG chains are linked to protein molecules
    (known as core proteins) by N- and O-glycosidic
    linkages. The diversity of proteoglycans is ?
    result of both the number of different core
    proteins and the large variety of different
    classes and length of the carbohydrate chains.

54
Fig. Proteoglycan structure
55
  • Because proteoglycans contain large numbers of
    GAGs, which are polyanions, large volumes of
    water and cations are trapped within their
    structure. As ? result, proteoglycan molecules
    occupy space that is thousands of times bigger
    that of ? densely packed molecule of the same
    mass. Proteoglycans contribute support and
    elasticity to tissues in which they occur.
    Consider, for example, the strength, flexibility,
    and resilience of cartilage. The structural
    diversity of proteoglycans allows them to serve ?
    variety of structural and functional roles in
    living organisms. Proteoglycans are particularly
    abundant in the extracellular matrix of
    connective tissue. Together with matrix proteins
    such as collagen, fibrinogen and laminin, they
    form an organized meshwork that provides strength
    and support to multicellular tissues.
    Proteoglycans are also present at the surface of
    cells, where they are directly bound with the
    plasma membrane. Although the function of these
    latter molecules is not yet clear, the suggestion
    has been made that they play an important role in
    membrane structure and cell-cell interactions.

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  • ? number of genetic diseases associated with
    proteoglycan metabolism, known as
    mucopolysaccharidoses, have been identified.
    Because proteoglycans are constantly being
    synthesized and degraded, their excessive
    accumulation (due to missing or defective
    lyzosomal enzymes) has very serious consequences.
    For example, in Hurler's syndrome, an autosomal
    recessive disorder (? disease type in which one
    copy of the defective gene is inherited from each
    parent), deficiency of ? specific enzyme results
    in accumulation of dermatan sulfate. Symptoms
    include mental retardation, skeletal deformity,
    and early childhood death. Glycoproteins are
    commonly defined as proteins that are covalently
    linked to carbohydrate through O- or N-linkages.
    The carbohydrate contain of glycoprotein varies
    from 1 to over 85 of total weight. The types of
    carbohydrate that are founded include
    monosaccharides and disaccharides such as those
    attached to the structural protein collagen and
    branched oligosaccharides on plasma
    glycoproteins. Although the glycoproteins are
    sometimes considered to include the
    proteoglycans, there appear to be sufficient
    structural reasons to examine them separately.

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  • These substances include glycoproteins of
    uronic acids, sulfate groups and disaccharide
    repeating units that are typical for
    proteoglycans. The carbohydrate groups of
    glycoproteins are linked to the polypeptide by
    either (1) an N-glycosidic linkage between
    N-acetylglucosamine (GlcNAc) and the aminoacid
    asparagine (Asn) or (2) an O-glycosidic linkage
    between N-acetylgalactosamine (GalNAc) and the
    hydroxyl group of the ?minoacids serine (Ser) or
    threonine (Thr). The former glycoprotein class is
    sometimes referred to as asparagine-linked the
    latter is often called mucin-type.

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  • Asparagine-linked carbohydrates. As was mentioned
    previously, three structural forms of
    asparagine-linked oligosaccharide occur in
    glycoproteins high- mannose, complex, and
    hybrid. High-mannose type is composed of GlcNAc
    and mannose. Complex-type may contain fructose,
    galactose, and sialic acid in addition to GlcNAc
    and mannose. Hybrid-type oligosaccharides contain
    features of both complex and high-mannose-type
    species. Despite these differences, the core
    structure of all N-linked oligosaccharides is the
    same. This core, which is constructed on ?
    membrane-bound lipid molecule, is covalently
    linked to asparagine during protein synthesis.
    Several additional reactions, which occur within
    the lumen of the endoplasmic reticulum and the
    Golgi complex, result in the final N-linked
    oligosaccharide structures.

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  • Mucin-type carbohydrate While all N-linked
    oligosaccharides are bound to protein via
    GlcNAc-Asn, the linking groups of O-glycosidic
    oligosaccharides are of several types. The most
    common of these is GalNAc-Ser (or GalNAc-Thr).
    Considerable mucin-type carbohydrate unit is
    disaccharide such as Gal-1,3-GalNAc, found in the
    antifreeze glycoprotein of antarctic fish
    (Figure), to the complex oligosaccharides of
    blood groups such as those of the ABO system.
  • Fig. Antifreeze glycoprotein structure.

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6. Lipids
  • Lipids differ from the other classes of
    naturally occurring biomolecules (carbohydrates,
    proteins, and nucleic acids), they are more
    soluble in non- or weakly polar solvents (diethyl
    ether, hexane, dichloromethane) than in water.
    They include a variety of structural types, a
    collection of which is introduced in this
    chapter. In spite of the number of different
    structural types, lipids share a common
    biosynthetic origin in that they are ultimately
    derived from glucose. During one stage of
    carbohydrate metabolism, called glycolysis,
    glucose is converted to lactic acid. Pyruvic acid
    is an intermediate product.

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Classification of lipids
62
  • Classification Lipids can be divided into two
    major classes on the basis of whether they
    undergo hydrolysis reactions in alkaline (basic)
    solution. Saponifiable lipids can be hydrolyzed
    under alkaline conditions to yield salts of fatty
    acids. Nonsaponifiable lipids do not undergo
    hydrolysis reactions in alkaline solution.
  • The basis of the nature of the products obtained
    on hydrolysis lipids are mainly divided into
    three type simple, compound and derived lipids.
  • 1. Simple lipids. These are esters of fatty acids
    and alcohols and thus on hydrolysis give fatty
    acids and alcohols. They may be of two types.
  • ?) Fats and oils. These are esters of fatty acids
    and glycerol (? trihydric alcohol). These are
    also known as glycerides.
  • b) Waxes. These are esters of long-chain fatty
    acids and long-chain monohydric alcohols or
    sterols.
  • 2 Compound lipids. Compound lipids are esters of
    fatty acids and alcohols in combination with
    other compound and thus on hydrolysis give fatty
    acids, alcohol and other compounds. On the basis
    of the nature of the other group, compound lipids
    may again be of following types.
  • ?) Phospholipids. These are fat like compounds
    containing phosphoric acid and ? nitrogen base.
  • b) Glycolipids. These are compounds containing ?
    fatty acid, ? carbohydrate, ? complex alcohol,
    and nitrogen, but n? phosphorus.
  • 3. Derived lipids. These compounds although do
    not contain an ester linkage but are obtained by
    the hydrolysis of simple and compound lipids.
    They may be fatty acids, alcohols and sterols.

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  • Lipids are organic compounds, found in living
    organisms, that are soluble in nonpolar organic
    solvents. Because compounds are classified as
    lipids on the basis of a physical property their
    solubility in an organic solventrather than as a
    result of their structures, lipids have a variety
    of structures and functions, as the following
    examples illustrate

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Functions of lipids
  • The most important role of lipids is as ?
    fuel. Much of the carbohydrates of the diet are
    converted to fat which is stored in various
    tissues and utilised at the time of requirement.
    Thus fat may be the major source of energy for
    many tissues. Actually, in some respects lipids
    (fats) are even superior to carbohydrates as
    source of energy.
  • Fatty acids with their flexible backbones
    can be stored in ? much more compact form than
    the highly spatially oriented and rigid glycogen
    structure. Thus fat storage provides economy in
    both weight and space. In addition to the above
    three reasons there are two other reasons for fat
    storage as an excellent form of energy.
  • As it is insoluble in water, it has been
    carried to the fat depots by the specialised
    transport proteins in the plasma.
  • It remains as ? stable and fixed reserve of
    energy until mobilized by enzymes which hydrolyse
    it to glycerol and fatty acids. The enzymes are
    under the control of various hormones and are
    activated under conditions where the body is
    involved in increased energy expenditure.

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  • Fat may also provide padding to protect the
    internal organs. Brain and nervous tissue are
    rich in certain lipids, ? fact which indicates
    the importance of these compounds to life.
  • Some compounds derived from lipids are
    important building blocks of biologically active
    materials ?.g. acetic acid can be used by the
    body to synthesize cholesterol and related
    compounds (hormones).
  • Lipoproteins are constituents of cell
    walls. The lipids present in lipoproteins
    constituting the cell walls are of the types of
    phospholipids. Since lipids are water insoluble
    they act as ideal barrier for preventing water
    soluble materials from passing freely between the
    intra- and extra-cellular fluids.
  • One more important function of dietary
    lipids is that of supplying the so-called
    essential fatty acids although there are several
    functions (essential fatty acids (EFA), none of
    them are well defined.

67
  • Fats and oils are naturally occurring mixtures
    of triacylglycerols, also called
    triglycerides.They differ in that fats are solids
    at room temperature and oils are liquids. We
    generally ignore this distinction and refer to
    both groups as fats. Triacylglycerols are built
    on a glycerol framework.
  • Simple triacylglycerines include similar fatty
    acids , mixed different. All
    three acyl groups in a triacylglycerol may be the
    same, all three may be different, or one may be
    different from the other two.

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Nomenclature, methods of getting of fats
For simple glycerides the name is made up of the
name of the alcohol (glycerol) or its radical
(glyceryl) and the name of the acid or the name
of the acid concerned is changed to suffix in.
For mixed glycerides, the position and names of
the acid groups are specified by Greek letters a,
ß, a or by the numerals 1, 2 and 3.
  • Methods of getting
  • O-acylation of alcohols
  • Allocation from plants melting out, pressing or
    extraction by organic solvents.

70
  • Fatty acids are carboxylic acids with long
    hydrocarbon chains. Because they are synthesized
    from acetate, a compound with two carbon atoms,
    most naturally occurring fatty acids contain an
    even number of carbon atoms and are unbranched.
    Fatty acids can be saturated with hydrogen (and
    therefore have no carboncarbon double bonds) or
    unsaturated (have carboncarbon double bonds).
    Fatty acids with more than one double bond are
    called polyunsaturated fatty acids. Double bonds
    in naturally occurring unsaturated fatty acids
    are never conjugated they are always separated
    by one methylene group. The physical properties
    of a fatty acid depend on the length of the
    hydrocarbon chain and the degree of unsaturation.
    As expected, the melting points of saturated
    fatty acids increase with increasing molecular
    weight because of increased Van-der-Waals
    interactions between the molecules

71
The most widespread fatty acids in natural oils
and fats
72
  • Double bonds are rigid structures, unsaturared
    acid molecules that contain them can occur in two
    isomeric forms cis and trans. In cis-isomers,
    for example, similar or identical groups are on
    the same side of double bond (a). When such
    groups are on opposite sides of a double bond,
    the molecule is said to be a trans-isomer (b)
  • The double bonds in unsaturated fatty acids
    generally have the cis configuration. This
    configuration produces a bend in the molecules,
    which prevents them from packing together as
    tightly as fully saturated fatty acids. As a
    result, unsaturated fatty acids have fewer
    intermolecular interactions and, therefore, lower
    melting points than saturated fatty acids with
    comparable molecular weights . The melting points
    of the unsaturated fatty acids decrease as the
    number of double bonds increases. For example, an
    18-carbon fatty acid melts at 69 C if it is
    saturated, at 13 C if it has one double bond, at
    if it has two -5 C o double bonds, and at -11 C
    if it has three double bonds.

73
  • Triacylglycerols, also called triglycerides,
    are compounds in which the three OH-groups of
    glycerol are esterified with fatty acids. If the
    three fatty acid components of a triacylglycerol
    are the same, the compound is called a simple
    triacylglycerol. Mixed triacylglycerols, on the
    other hand, contain two or three different fatty
    acid components and are more common than simple
    triacylglycerols. Not all triacylglycerol
    molecules from a single source are necessarily
    identical substances such as lard and olive oil,
    for example, are mixtures of several different
    triacylglycerols.

74
Triacylglycerols that are solids or semisolids
at room temperature are called fats. Fats are
usually obtained from animals and are composed
largely of triacylglycerols with either saturated
fatty acids or fatty acids with only one double
bond. The saturated fatty acid tails pack closely
together, giving the triacylglycerols relatively
high melting points, causing them to be solids at
room temperature. Liquid triacylglycerols are
called oils. Oils typically come from plant
products such as corn, soybeans, olives, and
peanuts. They are composed primarily of
triacylglycerols with unsaturated fatty acids
that cannot pack tightly together. Consequently,
they have relatively low melting points, causing
them to be liquids at room temperature.
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Hydrolysis of ? triacylglycerol
  • Hydrolysis of ? triacylglycerol is the reverse
    of the esterification reaction by which it wet
    formed. Complete hydrolysis of ? triacylglycerol
    molecule always gives one glycerol molecule and
    three fatty acid molecules as products.

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7. Chemical properties of fats
  • 1). Hydrolysis of fats with alkali (e.g., sodium
    hydroxide) yields salts of thefatty acids, and
    those of the alkali metals, such as sodium or
    potassium, are useig as soaps. Another name of
    this reaction saponification

The solubility of lipids in nonpolar organic
solvents results from their significant
hydrocarbon component. The hydrocarbon portion of
the compound is responsible for its oiliness or
fattiness. The word lipid comes from the Greek
lipos, which means fat.
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Characterization of fats. The composition,
quality and purity of ? given oil or fat is
determined by means of ? number of physical and
chemical tests. The usual physical tests include
determination of m, ?, specific gravity,
viscosity, etc. while the chemical tests include
determination of certain values discussed below.
  • 1. Acid number. It is the number of milligrams of
    potassium hydroxide required to neutralise the
    free fatty acids in 1g. of the oil or fat. Thus
    it indicates the amount of free fatty acids
    present in oil or fat. ? high acid value
    indicates ? stale oil or fat stored under
    improper conditions.
  • 2. Saponification number. It is number of
    milligrams of potassium hydroxide required to
    completely hydrolysis of l g. of the oil or fat.
    Thus it is ? measure of fatty acids present as
    esters in ? given oil or fat. The saponification
    value gives an idea about the molecular weight of
    fat or oil. The saponification number and
    molecular weight of an oil are inversely
    proportional to each other thus high
    saponification number indicates that the fat is
    made up of low molecular weight fatty acids and
    vice versa. It is also helpful in detecting
    adulteration of ? given fat by one of the lower
    or higher saponfication value.
  • 3. Iodine number. It is the number of grams of
    iodine that combine with 100 g. of oil or fat. It
    is ? measure of the degree of unsaturation of ?
    fat or oil ? high iodine number indicates ? high
    degree of unsaturation of the fatty acids of the
    fat.
  • Difference between saponification and acid
    numbers named ether number which characterizes
    contain of the remainders of fatty acids.

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  • 2). Oxidation of fates. Oxidation cases rancidity
    of fates. During oxidation form aldehydes with
    short carbon chain.

Oxidation at the soft conditions (water solution
of KMnO4) cases formation of glycols. At the
rigid conditions carbon skeleton destroys with
formation of remainders of carbonic acids with
shorter carbon chains.
79
Fats, which predominantly contain saturated fatty
acids, by oxidation form ketones.
80
  • 3). Hydrogenation. Some or all of the double
    bonds of polyunsaturated oils can be reduced by
    catalytic hydrogenation. Margarine and shortening
    are prepared by hydrogenating vegetable oils such
    as soybean oil and sunflower oil until they have
    the desired consistency. This process is called
    hardening of oils. The hydrogenation reaction
    must be carefully controlled, however, because
    reducing all the carboncarbon double bonds would
    produce a hard fat with the consistency of beef
    tallow. Quantity of H2 in grams, which are
    necessary for hydration of 10kg of fats
    (hydration number) characterizes unsaturating of
    fat.

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  • 4). Addition of halogens.

Iodine number for plants fats 100-200, for
animal fats 25-86, for fish fats 100-193.
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  • As might be expected from the properties of the
    fatty acids, fats have a predominance of
    saturated fatty acids, and oils are composed
    largely of unsaturated acids. Thus, the melting
    points of triglycerides reflect their
    composition, as shown by the following examples.
    Natural mixed triglycerides have somewhat lower
    melting points, the melting point of lard being
    near 30 º C, whereas olive oil melts near -6 º C.
    Since fats are valued over oils by some Northern
    European and North American populations,
    vegetable oils are extensively converted to solid
    triglycerides (e.g. Crisco) by partial
    hydrogenation of their unsaturated components.
    Some of the remaining double bonds are isomerized
    (to trans) in this operation. These saturated and
    trans-fatty acid glycerides in the diet have been
    linked to long-term health issues such as
    atherosclerosis.

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8. Phospholipids. Waxes.
  • Triacylglycerols arise, not by acylation of
    glycerol itself, but by a sequence of steps in
    which the first stage is acyl transfer to
    L-glycerol 3-phosphate (from reduction of
    dihydroxyacetone 3-phosphate, formed as described
    in Section 25.21). The product of this stage is
    called a phosphatidic acid.

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  • Hydrolysis of the phosphate ester function of
    the phosphatidic acid gives a diacylglycerol,
    which then reacts with a third acyl coenzyme A
    molecule to produce a triacylglycerol.
    Phosphatidic acids not only are intermediates in
    the biosynthesis of triacylglycerols but also are
    biosynthetic precursors of other members of a
    group of compounds called phosphoglycerides or
    glycerol phosphatides. Phosphorus-containing
    derivatives of lipids are known as phospholipids,
    and phosphoglycerides are one type of
    phospholipid. One important phospholipid is
    phosphatidylcholine, also called lecithin.
    Phosphatidylcholine is a mixture of diesters of
    phosphoric acid.

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  • An animated display of micelle formation is
    presented below. Notice the brownish material in
    the center of the three-dimensional drawing on
    the left. This illustrates a second important
    factor contributing to the use of these
    amphiphiles as cleaning agents. Micelles are able
    to encapsulate nonpolar substances such as grease
    within their hydrophobic center, and thus
    solubilize it so it is removed with the wash
    water. Since the micelles of anionic amphiphiles
    have a negatively charged surface, they repel one
    another and the nonpolar dirt is effectively
    emulsified. To summarize, the presence of a soap
    or a detergent in water facilitates the wetting
    of all parts of the object to be cleaned, and
    removes water-insoluble dirt by incorporation in
    micelles. If the animation has stopped, it may be
    restarted by clicking on it.

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Classification of phospholipids
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  • The oldest amphiphilic cleaning agent known to
    humans is soap. Soap is manufactured by the
    base-catalyzed hydrolysis (saponification) of
    animal fat (see below). Before sodium hydroxide
    was commercially available, a boiling solution of
    potassium carbonate leached from wood ashes was
    used. Soft potassium soaps were then converted to
    the harder sodium soaps by washing with salt
    solution. The importance of soap to human
    civilization is documented by history, but some
    problems associated with its use have been
    recognized. One of these is caused by the weak
    acidity (pKa ca. 4.9) of the fatty acids.
    Solutions of alkali metal soaps are slightly
    alkaline (pH 8 to 9) due to hydrolysis. If the pH
    of a soap solution is lowered by acidic
    contaminants, insoluble fatty acids precipitate
    and form a scum. A second problem is caused by
    the presence of calcium and magnesium salts in
    the water supply (hard water). These divalent
    cations cause aggregation of the micelles, which
    then deposit as a dirty scum.

89
Washing action of soaps
90
Waxes
  • Waxes are water-repelling solids that are part
    of the protective coatings of a number of living
    things, including the leaves of plants, the fur
    of animals, and the feathers of birds. They are
    usually mixtures of esters in which both the
    alkyl and acyl group are unbranched and contain a
    dozen or more carbon atoms. Beeswax, for example,
    contains the ester triacontyl hexadecanoate as
    one component of a complex mixture of
    hydrocarbons, alcohols, and esters.

91
  • Wax is ? mixture of esters of high molecular
    weight alcohols and high molecular weight fatty
    acids.
  • Waxes are sa??infied with great difficulty than
    fats and are not attacked by lipase. Although
    waxes may be saponified by prolonged boiling with
    alcoholic KOH, they are more easily saponified by
    treating ? solution of the wax in petroleum ether
    with absolute alcohol and metallic sodium, with
    sodium ethoxide. The saponification products ?f
    waxes are water-soluble soaps (sodium Its of
    higher fatty acids) while the water insoluble
    long-chain alcohols appear in the "unsaponifiable
    matter" fraction. Waxes contain about 31 -55 of
    the unsaponifiable matter, while fats and oils
    contain only 1 - 2 unsaponifiable matter.
  • Waxes dividing on animals (spermaceti, bees wax,
    lanoline and others) and plants (carnauba wax).

92
  • Bees wax. It contains esters derived from
    alcohols having 24 - 30 carbon atoms, include
    palmitate of miri??l alcohol (?30H61??) and
    n-hexacosanol (?26?53??).
  • ??3(C?2)14COOC30H61 ??3
    (C?2)14COOC26H53
  • miricyl patmitate n-
    hexacosanyl patmitate
  • Spermaceti. It is obtained from the head of the
    sperm whale. It is rich in ester of cetyl alcohol
    (?16?33??) and palmitinic acid ??3 (C ?2 )
    14COOC16H33 - cetyl palmitate
  • Spermaceti is used in making of candles.
  • Sperm Oil. It is ? liquid wax and occurs with
    spermaceti in the sperm whale. It is ? valuable
    lubricant used for delicate instruments, such as
    watches. It does not become gummy, as many oils
    do.
  • Carnauba wax. It is found in the leaves of the
    carnauba palm of Brazil. It is used as an
    ingredient in the manufacture of various wax
    polishes. Because waxes are very inert
    chemically, they make an excellent protective
    coating.
  • Lanolin or wool wax. It is obtained from wool and
    is used in making ointments and salves.

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9. Nonsaponifiable lipids
  • 1). Prostaglandins physiologically active
    substances with biogenic origin, stimulate smooth
    muscles and lowers blood pressure. All
    prostaglandins contain carboxyl group and 20
    carbon atoms in molecule, they are derivatives of
    eyicosanic acid.

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  • Research in physiology carried out in the 1930s
    established that the lipid fraction of semen
    contains small amounts of substances that exert
    powerful effects on smooth muscle. Sheep prostate
    glands proved to be a convenient source of this
    material and yielded a mixture of structurally
    related substances referred to collectively as
    prostaglandins. We now know that prostaglandins
    are present in almost all animal tissues, where
    they carry out a variety of regulatory functions.
    Prostaglandins are extremely potent substances
    and exert their physiological effects at very
    small concentrations. Because of this, their
    isolation was difficult, and it was not until
    1960 that the first members of this class,
    designated PGE1 and PGF1, were obtained as pure
    compounds.

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All the prostaglandins are 20-carbon carboxylic
acids and contain a cyclopentane ring. All have
hydroxyl groups at C-11 and C-15 (for the
numbering of the positions in prostaglandins).
Prostaglandins belonging to the F series have an
additional hydroxyl group at C-9, and a carbonyl
function is present at this position in the
various PGEs. The subscript numerals in their
abbreviated names indicate the number of double
bonds. Prostaglandins are believed to arise from
unsaturated C20-carboxylic acids such as
arachidonic acid. Mammals cannot biosynthesize
arachidonic acid directly.
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  • They obtain linoleic acid from vegetable oils
    in their diet and extend the carbon chain of
    linoleic acid from 18 to 20 carbons while
    introducing two more double bonds. Linoleic acid
    is said to be an essential fatty acid, forming
    part of the dietary requirement of mammals.
    Animals fed on diets that are deficient in
    linoleic acid grow poorly and suffer a number of
    other disorders, some of which are reversed on
    feeding them vegetable oils rich in linoleic acid
    and other polyunsaturated fatty acids. One
    function of these substances is to provide the
    raw materials for prostaglandin biosynthesis.

97
  • Physiological responses to prostaglandins
    encompass a variety of effects. Some
    prostaglandins relax bronchial muscle, others
    contract it. Some stimulate uterine contractions
    and have been used to induce therapeutic
    abortions. PGE1 dilates blood vessels and lowers
    blood pressure it inhibits the aggregation of
    platelets and offers promise as a drug to reduce
    the formation of blood clots. The long-standing
    question of the mode of action of aspirin has
    been addressed in terms of its effects on
    prostaglandin biosynthesis. Prostaglandin
    biosynthesis is the bodys response to tissue
    damage and is manifested by pain and inflammation
    at the affected site. Aspirin has been shown to
    inhibit the activity of an enzyme required for
    prostaglandin formation. Aspirin reduces pain and
    inflammationand probably fever as wellby
    reducing prostaglandin levels in the body.

98
  • Much of the fundamental work on prostaglandins
    and related compounds was carried out by Sune
    Bergström and Bengt Samuelsson of the Karolinska
    Institute (Sweden) and by Sir John Vane of the
    Wellcome Foundation (Great Britain). These three
    shared the Nobel Prize for physiology or medicine
    in 1982. Bergström began his research on
    prostaglandins because he was interested in the
    oxidation of fatty acids. That research led to
    the identification of a whole new class of
    biochemical mediators. Prostaglandin research has
    now revealed that other derivatives of oxidized
    polyunsaturated fatty acids, structurally
    distinct from the prostaglandins, are also
    physiologically important. These fatty acid
    derivatives include, for example, a group of
    substances known as the leukotrienes, which have
    been implicated as mediators in immunological
    processes.

99
  • Prostaglandins have cyclopentane ring.
    According to allocation of double bonds in
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Title: Di- and polysaccharides.


1
Lecture ? 15
  • Di- and polysaccharides.
  • Terpenes.

Ass. Medvid I.I. Ass. Burmas N.I
2
Outline
  • Oligosaccharides.
  • The following functions of carbohydrates in
    humans.
  • 3.Classification of disaccharides
  • maltose
  • cellobiose
  • lactose
  • saccharose.
  • 4. Polysaccharides (glucanes).
  • a) Homopolysaccharides
  • - Structure, composition and properties of
    cellulose.
  • - Structure, composition and properties of
    starch.
  • - Glycogen, dextranes, inuline, pectin compounds,
    chitin.
  • b) Heteropolysaccharides.
  • 5. Glycoconjugates.

3
  • 6. Lipids.
  • 7. Chemical properties of fats
  • 8. Phospholipids. Waxes.
  • 9. Nonsaponifiable lipids.
  • 10. Terpenes and terpenoids. Terpene
    biosynthesis.
  • 11. Classification of terpenes.
  • 12. Carotenoids.
  • 13. Steroids.
  • 14. Properties of cholesterol. Biosynthesis of
    cholesterol.
  • 15. Vitamins.
  • 16. Water-soluble vitamins.
  • 17.Water insoluble (lipid-soluble) vitamins.

4
  • Oligosaccharides.
  • The term oligosaccharide is often used for
    carbohydrates that consist of between two and ten
    monosaccharide units. Oligosaccharides are
    carbohydrates that contain from two to ten
    monosaccharide units.
  • Disaccharides are the most common type of
    oligosaccharide. Disaccharides are carbohydrates
    composed of two monosaccharide units covalently
    bonded to each other. Like monosaccharides,
    disaccharides are crystalline, water-soluble
    substances. Saccharose (table sugar) and lactose
    (milk sugar) are disaccharides. Within the human
    body, oligosaccharides are often found associated
    with proteins and lipids in complexes that have
    both structural and regulatory functions. Free
    oligosaccharides, other than disaccharides, are
    seldom encountered in biological systems
  • Complete hydrolysis of an oligosaccharide
    produces monosaccharides. Upon hydrolysis, ?
    disaccharide produces two monosaccharides, ?
    trisaccharide three monosaccharides, ?
    hexasaccharide six monosaccharides, and so on.

5
  • Carbohydrates are the most abundant class of
    bioorganic molecules on planet Earth. Although
    their abundance in the human body is relatively
    low, carbohydrates constitute about 75 by mass
    of dry plant materials.
  • Green (chlorophyll-containing) plants produce
    carbohydrates via photosynthesis. In this
    process, carbon dioxide from the air and water
    from the soil are the reactants, and sunlight
    absorbed by chlorophyll is the energy source.
  • Plants have two main uses for the carbohydrates
    they produce. In the form of cellulose,
    carbohydrates serve as structural elements, and
    in the form of starch, they provide energy
    reserves for the plants.
  • Dietary intake of plant materials is the major
    carbohydrate source for humans and animals. The
    average human diet should ideally be about
    two-thirds carbohydrate by mass.

6
  • 2. The following functions of carbohydrates in
    humans.
  • Carbohydrates have the following functions in
    humans
  • 1. Carbohydrate oxidation provides energy
  • 2. Carbohydrate storage, in the form of glycogen,
    provides ? short- term energy reserve.
  • 3. Carbohydrates supply carbon atoms for the
    synthesis of other biochemical substances
    (proteins, lipids, and nucleic acids).
  • 4. Carbohydrates form part of the structural
    framework of DNA and RNA molecules.
  • 5. Carbohydrate "markers" on cell surfaces play
    key roles in cell -cell recognition processes.

7
  • 3.Classification of disaccharides
  • (1) N?n-reducing disaccharides. In these
    disaccharides the two hexose units are linked
    together through their reducing (i ?. aldehydic
    or ketonic) groups which is , in aldoses
    and , in ketoses. Now in such cases since
    the reducing groups of both hexoses are lost, the
    resulting compound (disaccharide) will be
    non-reducing. Hence such disaccharides do not
    form osazone do not show mutarotation and do not
    react with reagents like Felings solution,
    Tollens reagent, etc. Important example of
    non-reducing disaccharides is saccharose.
  • (2) Reducing disaccharides. In these
    disaccharides, one hexose unit is linked through
    its reducing carbon to the non-reducing carbon
    (C4 or ?6) of the other Now since the reducing
    group of one of the hexoses is not involved, the
    resulting disaccharide will be ? reducing sugar.
    Maltose and lactose are examples of reducing
    disaccharides.

8
  • As mentioned earlier, disaccharides are those
    sugars which on hydrolysis give two moles of
    monosaccharides general these are sweet-testing
    crystalline, water-soluble substances, easily
    hydrolysed by enzymes and dilute mineral acids.
    The common disaccharides have the general formula
    C12H22O11 which during hydrolysis take one
    molecule of water to form two hexoses.
  • Disaccharides are formed by intermolecular
    dehydration between two monosaccharide molecules,
    e.g. In the formation of disaccharides, at least
    one monosaccharide unit is linked to the other
    through the glycosidic carbon atom. In other
    words we can say that in the formation of
    disaccharide, reducing property of at least one
    hexose unit is lost. Hence disaccharides may be
    considered as glycosides in which both components
    of the molecules are sugars. Disaccharides may
    exist in two types, namely non-reducing and
    reducing depending on the fact that ?1 of one
    hexose is linked to the carbonyl carbon at other
    carbon atom of other hexose. Weak oxidizing
    agents, such as Tollens, Feling's, and Benedict's
    solutions, oxidize the carbonyl group end of ?
    monosaccharide to give an -onic acid.

9
  • Disaccharides. ? monosaccharide that has cyclic
    forms (hemiacetal or hemiketal) can react with an
    alcoho1 to form ? glycoside (acetal or ketal).
    This same type of reaction can be used to produce
    ? disaccharide, ? carbohydrate in which two
    monosaccharides are bonded together. In
    disaccharide formation, one of the monosaccharide
    reactants functions as ? hemiacetal or hemiketal,
    and the other functions as an alcohol.
  • Monosaccharide monosaccharide disaccharide
    ?2O
  • The bond that links the two monosaccharides of ?
    disaccharide together is called ? glycosidic
    linkage. ? glycosidic linkage is the
    carbon-oxygen-carbon bond that joins the two
    components of ? glycoside together. The bond that
    links the two monosaccharides of ? disaccharide
    together is called ? glycosidic linkage. We now
    examine the structures and properties of four
    important disaccharides maltose, cellobiose,
    lactose, and saccharose. As we consider details
    of the structures of these compounds, we will
    find that the configuration (a or ß) at carbon-1
    of the reacting monosaccharides is often of prime
    importance.

10
  • Maltose, often called malt sugar, is produced
    by breaking down the polysaccharide starch, as
    takes place in plants when seeds germinate and in
    human beings during starch digestion. It is ?
    common ingredient in baby foods and is found in
    malted milk. Malt (germinated barley that has
    been baked and ground) contains maltose hence
    the name malt sugar. Structurally, maltose is
    made up of two D-glucopyranose units, one of
    which must be ?-D-glucose. The formation of
    maltose from two glucose molecules is as follows
  • ?-D-Glucose ?-D-Glucose
    ?-(1-4)-linkage

11
So, a-maltose can be named as 4-O-(a-D-glucopyrano
sido)-a-D-glucopyranose, ß-maltose
4-O-(a-D-glucopyranosido)-ß-D-glucopyranose.
12
  • The glycosidic linkage between the two glucose
    units is called an ?(1 - 4) linkage. The two
    ??-groups that form the linkage are attached,
    respectively, to carbon-1 of the first glucose
    unit (in an a configuration) and to carbon-4 of
    the second. Maltose is ? reducing sugar, because
    the glucose unit on the right has ? hemiacetal
    carbon atom (?-1).Thus this glucose unit can open
    and close it is in equilibrium with its
    open-chain aldehyde form. This means there are
    actually three forms of the maltose molecule
    ?-maltose, ?-maltose, and the open-chain form. In
    the solid state, the ?-form is dominant. The most
    important chemical reaction of maltose is
    hydrolysis. Hydrolysis of D-maltose, whether in ?
    laboratory flask or in ? living organism,
    produces two molecules of D-glucose.

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16
  • Cellobiose is produced as an intermediate in
    the hydrolysis of the polysaccharide cellulose.
    Like maltose, cellobiose contains two D-glucose
    monosaccharide units. It differs from maltose in
    one of D-glucose units - the one functioning as ?
    hemiacetal - must have ? ?-configuration instead
    of the ? configuration of maltose. This change in
    configuration gives ? ?(1-4) glycosidic linkage.

?-D-Glucose
?(1-4)-linkage
17
a-cellobiose can be named as 4-O-(ß-D-glucopyranos
ido)-a-D-glucopyranose, ß-cellobiose
4-O-(ß-D-glucopyranosido)-ß-D-glucopyranose.
18
  • Like maltose, cellobiose is a reducing sugar,
    has three isomeric forms in aqueous solution, and
    upon hydrolysis produces two D-glucose molecules.
    Despite these similarities, maltose and
    cellobiose have different biological behaviors.
    These differences are related to the
    stereochemistry of their glycosidic linkages.
    Maltase, the enzyme that breaks the
    glucose-glucose ?(1-4) linkage present in
    maltose, is found both in the human body and in
    yeast. Consequently, maltose is digested easily
    by humans and is readily fermented by yeast. Both
    the human body and yeast lack the enzyme
    cellobiase needed to break the glucose - glucose
    ?(1-4) linkage of cellobiose. Thus cellobiose
    cannot be digested by humans or fermented by
    yeast. In maltose and cellobiose, the two units
    of the disaccharide are identical - two glucose
    units in each case.
  • Maltose and cellobiose have different
    arrangement in space. In maltose molecule
    a-glycosidic linkage has axial arrangement, in
    cellobiose molecule ß-glycosidic linkage
    equatorial. Its cases club-similar structure of
    amylose and linear structure of cellulose.

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20
  • Lactose includes ?-D-galactopyranose unit and ?
    D-glucopyranose unit joined by ?-(1-4) glycosidic
    linkage

?-D-galactose ?-D-Glucose
?(1-4)-linkage
The glucose hemiacetal center is active when
galactose bonds to glucose in the formation of
lactose, so lactose is ? reducing sugar (the
glucose ring can open to give an
aldehyde).Lactose is the major sugar found in
milk. This accounts for its common name, milk
sugar. Enzymes in animal mammary glands take
glucose from the bloodstream and synthesize
lactose in ? four-step process. Epimerization of
glucose yields galactose, and then the ?(1-4)
linkage forms between ? galactose and ? glucose
unit. Lactose is an important ingredient in
commercially produced infant formulas that are
designed to simulate mother' s milk. Souring of
milk is caused by the conversion of lactose to
lactic acid by bacteria in the milk.
Pasteurization of milk is ? quick-heating process
that kills most of the bacteria and retards the
souring process. Lactose can be hydrolyzed by
acid or by the enzyme lactase, forming an
equimolar mixture of galactose and glucose. In
the human body, the galactose produced in such
way is then converted to glucose by other
enzymes. The genetic condition lactose
intolerance, an inability of the human digestive
system to hydrolyze lactose.
21
a-lactose can be named as 4-O-(ß-D-galactopyranosi
do)-a-D-glucopyranose, ß-lactose
4-O-(ß-D-galactopyranosido)-ß-D-glucopyranose. Arr
angement in space is similar to cellobiose
22
  • Saccharose, common table sugar, is the most
    abundant of all disaccharides and occurs
    throughout the plant kingdom. It is produced
    commercially from the juice of sugar cane and
    sugar beets. Sugar cane contains up to 20 by
    mass saccharose, and sugar beets contain up to 17
    by mass saccharose. The two monosaccharide
    units present in ?-D-saccharose molecule are
    ?-D-glucose in form of ?-D-glucopyranose and
    ?-D-fructose in form of ?-D-fructofuranose. The
    glycosidic linkage is not ? (1-4) linkage, as was
    in case with maltose, cellobiose, and lactose. It
    is instead an ?,?(1 - 2) glycosidic linkage. The
    ??-group on carbon-2 of D-fructose (the hemiketal
    carbon) reacts with the ??-group on carbon-l of
    D-glucose (the hemiacetal carbon).

23
Saccharose can be named as 2-O-(a-D-glucopyranosid
o)-ß-D-fructofuranose.
24
  • Saccharose, unlike maltose, cellobiose, and
    lactose, is ? non-reducing sugar. No helmiacetal
    or hemiketal center is present in the molecule,
    because the glycosidic linkage involves the
    reducing ends of both monosaccharides.
    Saccharose, in the solid state and in solution,
    exists in only one form - there are no ? and ?
    isomers, and an open-chain form is not possible.
    Saccharase, the enzyme needed to break the ?,?(1
    - 2) linkage in saccharose, is present in the
    human body. Hence saccharose is an easily
    digested substance.

25
  • Saccharose hydrolysis (digestion) produces an
    equimolar mixture of glucose and fructose called
    invert sugar. When saccharose is cooked with
    acid-containing foods such as fruits or berries,
    partial hydrolysis takes place, forming some
    invert sugar. Jams and jellies prepared in this
    manner are actually sweeter than the pure
    saccharose added to the original mixture, because
    one-to-one mixtures of glucose and fructose taste
    sweeter than saccharose.
  • Saccharose is dextrorotatory. On hydrolysis it
    gives one molecule of glucose and one molecule of
    fructose. Now since fructose is more strongly
    laevorotatory than the dextrorotatory property of
    glucose, the mixture (product) after hydrolysis
    will be laevorotatory. This reaction is also as
    inversion of sugar because the dextrorotatory
    case sugar is converted into laevorotatory
    product due to hydrolysis. The mixture of glucose
    and fructose is called invert sugar.

26
dextrorotatory
laevorotatory
27
  • 4. Polysaccharides (glucanes)
  • ? polysaccharides (glucanes) contains many
    monosaccharide units bonded to each other by
    glycosidic linkages. The number of monosaccharide
    units in polysaccharides varies from ? few
    hundred to hundreds of thousands. Polysaccharides
    are polymers. In some, the monosaccharides are
    bonded together in ? linear (unbranched) chain.
    In others, there is extensive branching of the
    chains. Unlike monosaccharides and most
    disaccharides, polysaccharides are not sweet and
    do not give positive reaction with Tollens,
    Benedicts, and Felings solutions. They have
    limited water solubility because of their size.
    However, the ??-groups present in molecule can
    individually become hydrated by water molecules.
    The result is usually ? thick colloidal
    suspension of the polysaccharide in water.
    Polysaccharides, such as flour and cornstarch,
    are often used as thickening agents in sauces,
    desserts, and gravy.

28
Linear and branched structure of polysaccharides
29
  • Although there are many naturally occurring
    polysaccharides, in this section we will focus on
    only four of them cellulose, starch, glycogen,
    and chitin. All play vital roles in living
    systems - cellulose and starch in plants,
    glycogen in humans and other animals, and chitin
    in arthropods.
  • Polysaccharides may be divided into two
    classes homopolysaccharides, which are composed
    of one type of monosaccharide units, and
    heteropolysaccharides, which contain two or more
    different types of monosaccharide units.
  • Starch, glycogen and cellulose are homoglycans
    as they are made of only glucose and are called
    glucanes or glucosanes. Homopolysaccharides which
    containe only pentoses called pentosanes, hexoses
    hexosanes. On the other hand,
    mucopolysaccharides like hyaluronic acid and
    chondroitine sulphate are heteroglycanes as they
    are made up of different monosaccharide units.
  • Common formula for pentosanes (C5H8O4)n, for
    hexosanes (C6H10O5)n.

30
  • Homopolysaccharides
  • Structure, composition and properties of
    cellulose.
  • Cellulose is the most abundant polysaccharide.
    It is the structural component of the cell walls
    of plants. Approximately half of all the carbon
    atoms in the plant kingdom are contained in
    cellulose molecules. Structurally, cellulose is ?
    linear (unbranched) D-glucose polymer in which
    the glucose units are linked by ?(1-4) glycosidic
    bonds.

31
  • At heating with mineral acids cellulose
    hydrolyzed by the following scheme

In cellulose glucopyranose remainders have linear
structure and hydrogen bonds
32
  • Typically, cellulose chains contain about 5000
    glucose units, which gives macromolecules with
    molecular masses of about 900,000. Cotton is
    almost pure cellulose (95 ) and wood is about
    50 cellulose. Even though it is ? glucose
    polymer, cellulose is not ? source of nutrition
    for human beings. Humans lack the enzymes capable
    of catalyzing the hydrolysis of ? (1- 4) linkages
    in cellulose. Even grazing animals have the
    enzymes necessary for cellulose digestion.
    However, the intestinal tracts of animals such as
    horses, cows, and sheep contain bacteria that
    produce cellulose, an enzyme that can hydrolyze ?
    (1- 4) linkages and produce free glucose from
    cellulose. Thus grasses and other plant materials
    are ? source of nutrition for grazing animals.
    The intestinal tracts of termites contain the
    same microorganisms, which enable termites to use
    wood as their source of food. Microorganisms in
    the soil can also metabolize cellulose, which
    makes possible the biodegradation of dead plants.
    Despite its nondigestibility, cellulose is still
    an important component of ? balanced diet. It
    serves as dietary fiber. Dietary fiber provides
    the digestive tract with "bulk" that helps move
    food through the intestinal tract and facilitates
    the excretion of solid wastes. Cellulose readily
    absorbs water, leading to softer stools and
    frequent bowel action. Links have been found
    between the length of time stools spend in the
    colon and possible colon cancer.

33
  • High-fiber food may also play ? role in weight
    control. Obesity is not seen in parts of the
    world where people eat large amounts of
    fiber-rich foods. Many of the weight-loss
    products on the market are composed of
    bulk-inducing fibers such as methylcellulose.
  • FIGURE. Cellulose microfibrils.
  • Some fibers bind lipids such as cholesterol and
    carry out them of the body with the feces. This
    lowers blood lipid concentrations and possibly
    the risk of heart and artery disease.

34
  • Structure, composition and properties of
    starch.
  • Starch, like cellulose, is ? polysaccharide
    containing only glucose units. It is the storage
    polysaccharide in plants. If excess of glucose
    enters ? plant cell, it is converted to starch
    and stored for later use. When the cell cannot
    get enough glucose from outside, it hydrolyzes
    starch to release glucose. Iodine is often used
    to test the presence of starch in solution.
    Starch-containing solutions turn ? dark blue when
    iodine is added. As starch is broken down through
    acid or enzymatic hydrolysis to glucose monomers,
    the blue color disappears. Two different
    polyglucose polysaccharides can be isolated from
    most starches amylose and amylopectin. Amylose,
    ? straight-chain glucose polymer, usually
    accounts for 15 20 of the starch
    amylopectin, ? highly branched glucose polymer,
    accounts for the remaining 80 85 of the
    starch.

35
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36
  • In amylose's structure, the glucose units are
    connected by ?(1- 4) glycosidic linkages.

  • Starch (amylose)
  • The number of glucose units present in an
    amylose chain depends on the source of the
    starch 200 350 monomer units are usually
    present. Amylopectin, the other polysaccharide in
    starch, is similar to amylose, but has ? high
    degree branched structure in the polymer. ? one
    branch link containe 20-25 glucose units. The
    number of glucose units present in an amylopectin
    chain consists of 1000 and more units. The branch
    points involve ?(1 6) linkages

Starch (amylopectin)
37
  • Because of the branching, amylopectin has ?
    larger average molecular mass than the linear
    amylose. The average molecular mass of amylose is
    40000 or more it is 1-6 mln. for amylopectin.
    Note that all of the glycosidic linkages in
    starch (both amylose and amylopectin) are of the
    ?-type. In amylose, they are all ?(1 - 4) in
    amylopectin, both ?(1 -4) and ?(1 -6) linkages
    are present. Because ? linkages can be broken
    through hydrolysis within the human digestive
    tract (with the help of the enzyme amylase),
    starch has nutritional value for humans. The
    starches present in potatoes and cereal grains
    (wheat, rice, corn, etc.) account for
    approximately two-thirds of the world' s food
    consumption.
  • Fermentayion hydrolysis of starch is shown below

38
  • Glycogen, chitin.
  • Glycogen, like cellulose and starch, is ?
    polysaccharide containing only glucose units. It
    is the glucose storage polysaccharide in humans
    and animals. Its function is thus similar to that
    of starch in plants, and it is sometimes referred
    to as animal starch. Liver cells and muscle cells
    are the storage sites for glycogen in humans.
    Glycogen has ? structure similar to that of
    amylopectin all glycosidic linkages are of the
    ?-type, and both (1-4) and (1-6) linkages are
    present. Glycogen and amylopectin differ in the
    number of glucose units between branches and the
    total number of glucose units present in ?
    molecule. Glycogen is about three times more
    highly branched than amylopectin, and it is much
    larger, with ? molar mass. ? one branch link
    containe 8-12 glucose units, rare 2- 4. When
    excess of glucose is present in the blood
    (normally from eating too much starch), the liver
    and muscle tissue convert the excess of glucose
    to glycogen, which is then stored in these
    tissues. Whenever the glucose blood level drops
    (from exercise, fasting, or normal activities),
    some stored glycogen is hydrolyzed back to
    glucose. These two opposing processes are called
    glycogenesis and glycogenolysis, the formation
    and decomposition of glycogen, respectively.

39
  • Glycogen is an ideal storage form for glucose.
    The large size of these macromolecules prevents
    them from diffusing out of cells. Also,
    conversion of glucose to glycogen reduces osmotic
    pressure. Cells would burst because of increased
    osmotic pressure if all of the glucose in
    glycogen were present in cells in free form. High
    concentrations of glycogen in ? cell sometimes
    cases precipitate or crystallize into glycogen
    granules. These granules are discernible in
    photographs of cells under electron microscope
    magnification. The glucose polymers amylose,
    amylopectin, and glycogen compare as follows in
    molecular size and degree of branching
  • Amylose Up to 1000 glucose units no branching
  • Amylopectin Up to 100,000 glucose units branch
    points every 20-25 glucose units
  • Glycogen Up to 1,000,000 glucose units branch
    points every 8-12 glucose units

40
  • FIGURE. Structure of amylopectine (?), glycogen
    (b)

41
Dextranes
  • Dextranes have bacterial origin, contain
    remainders of a-D-glucopyranose. Dextranes obtain
    from saccharose at the present of bacterium
    (Leuconostoc mesenteroides). The main type of
    bond is a-1,6-glycosidic bond, in place of
    branching a-1,4- and a-1,3-glycosidic bonds.
    The average molecular mass of dextranes is few
    millions. Partly hydrolyzed dextranes (m. m.
    40000-800000) use in pharmacy as plasmasubstitute
    (Polyglucin, Reopolyglucin).

42
Inuline
  • Inuline reserve polysaccharide, present in
    plants. Inuline has linear structure and consists
    of remainders of ß-D-fructofuranose, joined by
    2,1-glycosidic bonds, in the end of inuline is
    a-D-glucopyranose remainder (like saccharose).
    Molecular mass of inuline is up to 6000. Use for
    obtaining of D-fructose.

43
Pectin compounds
  • Pectin compounds (pectins) polysaccharides
    consist of polygalacturonic acid, which contain
    remainders of a-D-galacturonic acid joined by
    1,4-glycosidic bonds. Part of carboxyl grups
    present in appearance of methyl ether. Water
    solutions of pectins form stable gels. Pectins
    have antiulcer properties.

44
  • Chitin is ? polysaccharide that is similar to
    cellulose in both function and structure. Its
    function is to give rigidity to the exoskeletons
    of crabs, lobsters, shrimp, insects, and other
    arthropods. It also occurs in the cell walls of
    fungi. Structurally, chitin is ? linear polymer
    (no branching) with all ?(1- 4) glycosidic
    linkages, as in cellulose. Chitin differs from
    cellulose in that the monosaccharide present is
    an N-acetylamino derivative of D-glucose.

45
  • Heteropolysaccharides.
  • Unlike all the polysaccharides we have
    discussed up to this point, mucopolysaccharides
    are heteropolysaccharides rather than
    homopolysaccharides.
  • Mucopolysaccharides are compounds that occur in
    connective tissue associated with joints in
    animals and humans. Their function is primarily
    that of lubrication, ? necessary requirement if
    movement is to occur. The name mucopolysaccharide
    comes from the highly viscous, gelatinous
    (mucus-like) consistency of these substances in
    aqueous solution.
  • ? heteropolysaccharide is ? polysaccharide in
    which more than one (usually two) type of
    monosaccharide unit is present.
  • One of the most common mucopolysaccharides is
    hyaluronic acid, ? heteropolysaccharide in which
    the following two glucose derivatives alternate
    in the structure.

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  • It is ? highly viscous substance and has ?
    molecular weight in several hundred millions.
    Hyaluronic acid is ? principal component of the
    ground substance of connective tissue. Among
    other places it is found in skin, synovial fluid,
    vitreous hemour of the eye, and umbilical cord.
    It exercises ? cementing function in the tissues
    and capillary walls, and forms ? coating gel
    round the ovum. It accounts for about 80 of the
    viscosity of synovial fluid which contains about
    0. 02 0.05 of hyaluronate. Repeat part of
    hyaluronic acid is D-glucuronic acid and
    N-acetyl-D-glucosamine joined by ß-1,3-glycosidic
    bond, between disaccharide fragments ß-1,4.
    Molecular mass of hyaluronic acid is from 1600 to
    6400.
  • (1,4)-O-?-D-Glucopyranosyluronic
    acid-(1,3)-2-acetamino-2-dezoxy-?-D-glucopyranose.

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  • Hyaluronic acid is split up by the enzyme
    hyalurosidase into ? number of small molecule. If
    fluid containing this enzyme is injected into ?
    tissue it spreads rapidly, from the site of
    injection and thus this enzyme is sometimes
    referred as the spreading factor. It is found
    in relatively high concentration in the testis
    and seminal fluid, in the venoms of certain
    snakes and insects, and in some bacteria. The
    enzyme also has ? physiological role in
    fertilization. The sperm is rich in the enzyme
    and the former can thus advance better in the
    cervical canal and finally penetrates the ovum.

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  • Chondroitin sulfate. It has similar structure
    as hyaluronic acid with the difference that the
    N-acetyl-D-glucosamine unit of the molecule is
    replaced by N-acetyl-D-galactosamine unit with
    sulphate group. Repeat part of chondroitin
    sulphate is D-glucuronic acid and
    N-acetyl-D-galactosamine which contains sulfate
    group. Inside of disaccharide fragment is
    ß-1,3-glycosidic bond between fragments ß-1,4.
    Sulfate group forms ether bond with hydroxyl
    group of N-acetyl-D-galactosamine in location 4
    (chondroitin-4-sulfate) or in location 6
    (chondroitin-6-sulfate). Chondroitin sulfates are
    found in cartilage, bone, heart valves, tendons
    and cornea.
  • (1,4)-O-?-D-Glucopyranosyluronic
    acid-(1,3)-2-acetamino-2-dezoxy-6-O-sulfo-?-D-gala
    ctopyranose.

49
Hydrocarbon chains of chondroitin-4-sulfate
contain up to 150 disaccharides remainders,
joined in organism by O-glycosidic bonds with
hydroxyl groups of aminoacid remainders.
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  • Dermatan sulfate. (Varying amounts of
    D-glucuronic acid may be present. Concentration
    increases during aging process.)
  • (1,4)-O-?-L-idopyranosyluronic acid-(1,3)-2-acetam
    ino-2-dezoxy-4-O-sulfo-?-D-galactopyranose.

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  • Heparin. It is naturally occurring
    anticoagulant found mainly in the liver, and also
    in lung, spleen, kidney and intestinal mucosa. It
    prevents blood clotting by inhibiting the
    prothrombin-thrombin conversion and thus
    eliminating the thrombin effect on fibrinogen.
    Repeat part of heparin consists of D-glucosamin
    and uronic acid, joined by a-1,4-glycosidic
    bonds. As uronic acid in heparin present
    L-iduronic acid or, very rare, D-glucuronic acid.
    Remainders of glucosamine and L-iduronic acid
    partly sulfonated. Molecular mass of heparin is
    16000-20000.

(1,4)-O-?-D-idupyranosyluronic acid-2-O-sulfo-(1,4
)-2-sulfamino-2-dezoxy-6-O-sulfo-?-D-glucopyranose
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  • 5. Glycoconjugates.
  • The compounds that result from the covalent
    linkages of carbohydrate molecules to both
    proteins and lipids are collectively known as the
    glycoconjugates. These substances have profound
    effects on the function of individual cells, as
    well as the cell-cell interactions of
    multicellular organisms. There are two classes of
    carbohydrate-protein conjugate proteoglycans and
    glycoproteins. Although both molecular types
    contain ???bohydrate and protein, their
    structures and functions appear, in general, to
    be substantially different. The glycolipids,
    which are oligosaccharide-containing lipid
    molecules, are found predominantly on the outer
    surface of plasma membranes.

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  • Proteoglycans are distinguished from the common
    glycoproteins by their extremely high
    carbohydrate content, which may constitute as
    much as 95 of the dry weight of such molecules.
    These molecules are found predominantly in the
    extracellular matrix (intercellular material) of
    tissues. All proteoglycans contain GAG chains.
    The GAG chains are linked to protein molecules
    (known as core proteins) by N- and O-glycosidic
    linkages. The diversity of proteoglycans is ?
    result of both the number of different core
    proteins and the large variety of different
    classes and length of the carbohydrate chains.

54
Fig. Proteoglycan structure
55
  • Because proteoglycans contain large numbers of
    GAGs, which are polyanions, large volumes of
    water and cations are trapped within their
    structure. As ? result, proteoglycan molecules
    occupy space that is thousands of times bigger
    that of ? densely packed molecule of the same
    mass. Proteoglycans contribute support and
    elasticity to tissues in which they occur.
    Consider, for example, the strength, flexibility,
    and resilience of cartilage. The structural
    diversity of proteoglycans allows them to serve ?
    variety of structural and functional roles in
    living organisms. Proteoglycans are particularly
    abundant in the extracellular matrix of
    connective tissue. Together with matrix proteins
    such as collagen, fibrinogen and laminin, they
    form an organized meshwork that provides strength
    and support to multicellular tissues.
    Proteoglycans are also present at the surface of
    cells, where they are directly bound with the
    plasma membrane. Although the function of these
    latter molecules is not yet clear, the suggestion
    has been made that they play an important role in
    membrane structure and cell-cell interactions.

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  • ? number of genetic diseases associated with
    proteoglycan metabolism, known as
    mucopolysaccharidoses, have been identified.
    Because proteoglycans are constantly being
    synthesized and degraded, their excessive
    accumulation (due to missing or defective
    lyzosomal enzymes) has very serious consequences.
    For example, in Hurler's syndrome, an autosomal
    recessive disorder (? disease type in which one
    copy of the defective gene is inherited from each
    parent), deficiency of ? specific enzyme results
    in accumulation of dermatan sulfate. Symptoms
    include mental retardation, skeletal deformity,
    and early childhood death. Glycoproteins are
    commonly defined as proteins that are covalently
    linked to carbohydrate through O- or N-linkages.
    The carbohydrate contain of glycoprotein varies
    from 1 to over 85 of total weight. The types of
    carbohydrate that are founded include
    monosaccharides and disaccharides such as those
    attached to the structural protein collagen and
    branched oligosaccharides on plasma
    glycoproteins. Although the glycoproteins are
    sometimes considered to include the
    proteoglycans, there appear to be sufficient
    structural reasons to examine them separately.

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  • These substances include glycoproteins of
    uronic acids, sulfate groups and disaccharide
    repeating units that are typical for
    proteoglycans. The carbohydrate groups of
    glycoproteins are linked to the polypeptide by
    either (1) an N-glycosidic linkage between
    N-acetylglucosamine (GlcNAc) and the aminoacid
    asparagine (Asn) or (2) an O-glycosidic linkage
    between N-acetylgalactosamine (GalNAc) and the
    hydroxyl group of the ?minoacids serine (Ser) or
    threonine (Thr). The former glycoprotein class is
    sometimes referred to as asparagine-linked the
    latter is often called mucin-type.

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  • Asparagine-linked carbohydrates. As was mentioned
    previously, three structural forms of
    asparagine-linked oligosaccharide occur in
    glycoproteins high- mannose, complex, and
    hybrid. High-mannose type is composed of GlcNAc
    and mannose. Complex-type may contain fructose,
    galactose, and sialic acid in addition to GlcNAc
    and mannose. Hybrid-type oligosaccharides contain
    features of both complex and high-mannose-type
    species. Despite these differences, the core
    structure of all N-linked oligosaccharides is the
    same. This core, which is constructed on ?
    membrane-bound lipid molecule, is covalently
    linked to asparagine during protein synthesis.
    Several additional reactions, which occur within
    the lumen of the endoplasmic reticulum and the
    Golgi complex, result in the final N-linked
    oligosaccharide structures.

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  • Mucin-type carbohydrate While all N-linked
    oligosaccharides are bound to protein via
    GlcNAc-Asn, the linking groups of O-glycosidic
    oligosaccharides are of several types. The most
    common of these is GalNAc-Ser (or GalNAc-Thr).
    Considerable mucin-type carbohydrate unit is
    disaccharide such as Gal-1,3-GalNAc, found in the
    antifreeze glycoprotein of antarctic fish
    (Figure), to the complex oligosaccharides of
    blood groups such as those of the ABO system.
  • Fig. Antifreeze glycoprotein structure.

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6. Lipids
  • Lipids differ from the other classes of
    naturally occurring biomolecules (carbohydrates,
    proteins, and nucleic acids), they are more
    soluble in non- or weakly polar solvents (diethyl
    ether, hexane, dichloromethane) than in water.
    They include a variety of structural types, a
    collection of which is introduced in this
    chapter. In spite of the number of different
    structural types, lipids share a common
    biosynthetic origin in that they are ultimately
    derived from glucose. During one stage of
    carbohydrate metabolism, called glycolysis,
    glucose is converted to lactic acid. Pyruvic acid
    is an intermediate product.

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Classification of lipids
62
  • Classification Lipids can be divided into two
    major classes on the basis of whether they
    undergo hydrolysis reactions in alkaline (basic)
    solution. Saponifiable lipids can be hydrolyzed
    under alkaline conditions to yield salts of fatty
    acids. Nonsaponifiable lipids do not undergo
    hydrolysis reactions in alkaline solution.
  • The basis of the nature of the products obtained
    on hydrolysis lipids are mainly divided into
    three type simple, compound and derived lipids.
  • 1. Simple lipids. These are esters of fatty acids
    and alcohols and thus on hydrolysis give fatty
    acids and alcohols. They may be of two types.
  • ?) Fats and oils. These are esters of fatty acids
    and glycerol (? trihydric alcohol). These are
    also known as glycerides.
  • b) Waxes. These are esters of long-chain fatty
    acids and long-chain monohydric alcohols or
    sterols.
  • 2 Compound lipids. Compound lipids are esters of
    fatty acids and alcohols in combination with
    other compound and thus on hydrolysis give fatty
    acids, alcohol and other compounds. On the basis
    of the nature of the other group, compound lipids
    may again be of following types.
  • ?) Phospholipids. These are fat like compounds
    containing phosphoric acid and ? nitrogen base.
  • b) Glycolipids. These are compounds containing ?
    fatty acid, ? carbohydrate, ? complex alcohol,
    and nitrogen, but n? phosphorus.
  • 3. Derived lipids. These compounds although do
    not contain an ester linkage but are obtained by
    the hydrolysis of simple and compound lipids.
    They may be fatty acids, alcohols and sterols.

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  • Lipids are organic compounds, found in living
    organisms, that are soluble in nonpolar organic
    solvents. Because compounds are classified as
    lipids on the basis of a physical property their
    solubility in an organic solventrather than as a
    result of their structures, lipids have a variety
    of structures and functions, as the following
    examples illustrate

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Functions of lipids
  • The most important role of lipids is as ?
    fuel. Much of the carbohydrates of the diet are
    converted to fat which is stored in various
    tissues and utilised at the time of requirement.
    Thus fat may be the major source of energy for
    many tissues. Actually, in some respects lipids
    (fats) are even superior to carbohydrates as
    source of energy.
  • Fatty acids with their flexible backbones
    can be stored in ? much more compact form than
    the highly spatially oriented and rigid glycogen
    structure. Thus fat storage provides economy in
    both weight and space. In addition to the above
    three reasons there are two other reasons for fat
    storage as an excellent form of energy.
  • As it is insoluble in water, it has been
    carried to the fat depots by the specialised
    transport proteins in the plasma.
  • It remains as ? stable and fixed reserve of
    energy until mobilized by enzymes which hydrolyse
    it to glycerol and fatty acids. The enzymes are
    under the control of various hormones and are
    activated under conditions where the body is
    involved in increased energy expenditure.

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  • Fat may also provide padding to protect the
    internal organs. Brain and nervous tissue are
    rich in certain lipids, ? fact which indicates
    the importance of these compounds to life.
  • Some compounds derived from lipids are
    important building blocks of biologically active
    materials ?.g. acetic acid can be used by the
    body to synthesize cholesterol and related
    compounds (hormones).
  • Lipoproteins are constituents of cell
    walls. The lipids present in lipoproteins
    constituting the cell walls are of the types of
    phospholipids. Since lipids are water insoluble
    they act as ideal barrier for preventing water
    soluble materials from passing freely between the
    intra- and extra-cellular fluids.
  • One more important function of dietary
    lipids is that of supplying the so-called
    essential fatty acids although there are several
    functions (essential fatty acids (EFA), none of
    them are well defined.

67
  • Fats and oils are naturally occurring mixtures
    of triacylglycerols, also called
    triglycerides.They differ in that fats are solids
    at room temperature and oils are liquids. We
    generally ignore this distinction and refer to
    both groups as fats. Triacylglycerols are built
    on a glycerol framework.
  • Simple triacylglycerines include similar fatty
    acids , mixed different. All
    three acyl groups in a triacylglycerol may be the
    same, all three may be different, or one may be
    different from the other two.

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Nomenclature, methods of getting of fats
For simple glycerides the name is made up of the
name of the alcohol (glycerol) or its radical
(glyceryl) and the name of the acid or the name
of the acid concerned is changed to suffix in.
For mixed glycerides, the position and names of
the acid groups are specified by Greek letters a,
ß, a or by the numerals 1, 2 and 3.
  • Methods of getting
  • O-acylation of alcohols
  • Allocation from plants melting out, pressing or
    extraction by organic solvents.

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  • Fatty acids are carboxylic acids with long
    hydrocarbon chains. Because they are synthesized
    from acetate, a compound with two carbon atoms,
    most naturally occurring fatty acids contain an
    even number of carbon atoms and are unbranched.
    Fatty acids can be saturated with hydrogen (and
    therefore have no carboncarbon double bonds) or
    unsaturated (have carboncarbon double bonds).
    Fatty acids with more than one double bond are
    called polyunsaturated fatty acids. Double bonds
    in naturally occurring unsaturated fatty acids
    are never conjugated they are always separated
    by one methylene group. The physical properties
    of a fatty acid depend on the length of the
    hydrocarbon chain and the degree of unsaturation.
    As expected, the melting points of saturated
    fatty acids increase with increasing molecular
    weight because of increased Van-der-Waals
    interactions between the molecules

71
The most widespread fatty acids in natural oils
and fats
72
  • Double bonds are rigid structures, unsaturared
    acid molecules that contain them can occur in two
    isomeric forms cis and trans. In cis-isomers,
    for example, similar or identical groups are on
    the same side of double bond (a). When such
    groups are on opposite sides of a double bond,
    the molecule is said to be a trans-isomer (b)
  • The double bonds in unsaturated fatty acids
    generally have the cis configuration. This
    configuration produces a bend in the molecules,
    which prevents them from packing together as
    tightly as fully saturated fatty acids. As a
    result, unsaturated fatty acids have fewer
    intermolecular interactions and, therefore, lower
    melting points than saturated fatty acids with
    comparable molecular weights . The melting points
    of the unsaturated fatty acids decrease as the
    number of double bonds increases. For example, an
    18-carbon fatty acid melts at 69 C if it is
    saturated, at 13 C if it has one double bond, at
    if it has two -5 C o double bonds, and at -11 C
    if it has three double bonds.

73
  • Triacylglycerols, also called triglycerides,
    are compounds in which the three OH-groups of
    glycerol are esterified with fatty acids. If the
    three fatty acid components of a triacylglycerol
    are the same, the compound is called a simple
    triacylglycerol. Mixed triacylglycerols, on the
    other hand, contain two or three different fatty
    acid components and are more common than simple
    triacylglycerols. Not all triacylglycerol
    molecules from a single source are necessarily
    identical substances such as lard and olive oil,
    for example, are mixtures of several different
    triacylglycerols.

74
Triacylglycerols that are solids or semisolids
at room temperature are called fats. Fats are
usually obtained from animals and are composed
largely of triacylglycerols with either saturated
fatty acids or fatty acids with only one double
bond. The saturated fatty acid tails pack closely
together, giving the triacylglycerols relatively
high melting points, causing them to be solids at
room temperature. Liquid triacylglycerols are
called oils. Oils typically come from plant
products such as corn, soybeans, olives, and
peanuts. They are composed primarily of
triacylglycerols with unsaturated fatty acids
that cannot pack tightly together. Consequently,
they have relatively low melting points, causing
them to be liquids at room temperature.
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Hydrolysis of ? triacylglycerol
  • Hydrolysis of ? triacylglycerol is the reverse
    of the esterification reaction by which it wet
    formed. Complete hydrolysis of ? triacylglycerol
    molecule always gives one glycerol molecule and
    three fatty acid molecules as products.

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7. Chemical properties of fats
  • 1). Hydrolysis of fats with alkali (e.g., sodium
    hydroxide) yields salts of thefatty acids, and
    those of the alkali metals, such as sodium or
    potassium, are useig as soaps. Another name of
    this reaction saponification

The solubility of lipids in nonpolar organic
solvents results from their significant
hydrocarbon component. The hydrocarbon portion of
the compound is responsible for its oiliness or
fattiness. The word lipid comes from the Greek
lipos, which means fat.
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Characterization of fats. The composition,
quality and purity of ? given oil or fat is
determined by means of ? number of physical and
chemical tests. The usual physical tests include
determination of m, ?, specific gravity,
viscosity, etc. while the chemical tests include
determination of certain values discussed below.
  • 1. Acid number. It is the number of milligrams of
    potassium hydroxide required to neutralise the
    free fatty acids in 1g. of the oil or fat. Thus
    it indicates the amount of free fatty acids
    present in oil or fat. ? high acid value
    indicates ? stale oil or fat stored under
    improper conditions.
  • 2. Saponification number. It is number of
    milligrams of potassium hydroxide required to
    completely hydrolysis of l g. of the oil or fat.
    Thus it is ? measure of fatty acids present as
    esters in ? given oil or fat. The saponification
    value gives an idea about the molecular weight of
    fat or oil. The saponification number and
    molecular weight of an oil are inversely
    proportional to each other thus high
    saponification number indicates that the fat is
    made up of low molecular weight fatty acids and
    vice versa. It is also helpful in detecting
    adulteration of ? given fat by one of the lower
    or higher saponfication value.
  • 3. Iodine number. It is the number of grams of
    iodine that combine with 100 g. of oil or fat. It
    is ? measure of the degree of unsaturation of ?
    fat or oil ? high iodine number indicates ? high
    degree of unsaturation of the fatty acids of the
    fat.
  • Difference between saponification and acid
    numbers named ether number which characterizes
    contain of the remainders of fatty acids.

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  • 2). Oxidation of fates. Oxidation cases rancidity
    of fates. During oxidation form aldehydes with
    short carbon chain.

Oxidation at the soft conditions (water solution
of KMnO4) cases formation of glycols. At the
rigid conditions carbon skeleton destroys with
formation of remainders of carbonic acids with
shorter carbon chains.
79
Fats, which predominantly contain saturated fatty
acids, by oxidation form ketones.
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  • 3). Hydrogenation. Some or all of the double
    bonds of polyunsaturated oils can be reduced by
    catalytic hydrogenation. Margarine and shortening
    are prepared by hydrogenating vegetable oils such
    as soybean oil and sunflower oil until they have
    the desired consistency. This process is called
    hardening of oils. The hydrogenation reaction
    must be carefully controlled, however, because
    reducing all the carboncarbon double bonds would
    produce a hard fat with the consistency of beef
    tallow. Quantity of H2 in grams, which are
    necessary for hydration of 10kg of fats
    (hydration number) characterizes unsaturating of
    fat.

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  • 4). Addition of halogens.

Iodine number for plants fats 100-200, for
animal fats 25-86, for fish fats 100-193.
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  • As might be expected from the properties of the
    fatty acids, fats have a predominance of
    saturated fatty acids, and oils are composed
    largely of unsaturated acids. Thus, the melting
    points of triglycerides reflect their
    composition, as shown by the following examples.
    Natural mixed triglycerides have somewhat lower
    melting points, the melting point of lard being
    near 30 º C, whereas olive oil melts near -6 º C.
    Since fats are valued over oils by some Northern
    European and North American populations,
    vegetable oils are extensively converted to solid
    triglycerides (e.g. Crisco) by partial
    hydrogenation of their unsaturated components.
    Some of the remaining double bonds are isomerized
    (to trans) in this operation. These saturated and
    trans-fatty acid glycerides in the diet have been
    linked to long-term health issues such as
    atherosclerosis.

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8. Phospholipids. Waxes.
  • Triacylglycerols arise, not by acylation of
    glycerol itself, but by a sequence of steps in
    which the first stage is acyl transfer to
    L-glycerol 3-phosphate (from reduction of
    dihydroxyacetone 3-phosphate, formed as described
    in Section 25.21). The product of this stage is
    called a phosphatidic acid.

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  • Hydrolysis of the phosphate ester function of
    the phosphatidic acid gives a diacylglycerol,
    which then reacts with a third acyl coenzyme A
    molecule to produce a triacylglycerol.
    Phosphatidic acids not only are intermediates in
    the biosynthesis of triacylglycerols but also are
    biosynthetic precursors of other members of a
    group of compounds called phosphoglycerides or
    glycerol phosphatides. Phosphorus-containing
    derivatives of lipids are known as phospholipids,
    and phosphoglycerides are one type of
    phospholipid. One important phospholipid is
    phosphatidylcholine, also called lecithin.
    Phosphatidylcholine is a mixture of diesters of
    phosphoric acid.

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  • An animated display of micelle formation is
    presented below. Notice the brownish material in
    the center of the three-dimensional drawing on
    the left. This illustrates a second important
    factor contributing to the use of these
    amphiphiles as cleaning agents. Micelles are able
    to encapsulate nonpolar substances such as grease
    within their hydrophobic center, and thus
    solubilize it so it is removed with the wash
    water. Since the micelles of anionic amphiphiles
    have a negatively charged surface, they repel one
    another and the nonpolar dirt is effectively
    emulsified. To summarize, the presence of a soap
    or a detergent in water facilitates the wetting
    of all parts of the object to be cleaned, and
    removes water-insoluble dirt by incorporation in
    micelles. If the animation has stopped, it may be
    restarted by clicking on it.

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Classification of phospholipids
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  • The oldest amphiphilic cleaning agent known to
    humans is soap. Soap is manufactured by the
    base-catalyzed hydrolysis (saponification) of
    animal fat (see below). Before sodium hydroxide
    was commercially available, a boiling solution of
    potassium carbonate leached from wood ashes was
    used. Soft potassium soaps were then converted to
    the harder sodium soaps by washing with salt
    solution. The importance of soap to human
    civilization is documented by history, but some
    problems associated with its use have been
    recognized. One of these is caused by the weak
    acidity (pKa ca. 4.9) of the fatty acids.
    Solutions of alkali metal soaps are slightly
    alkaline (pH 8 to 9) due to hydrolysis. If the pH
    of a soap solution is lowered by acidic
    contaminants, insoluble fatty acids precipitate
    and form a scum. A second problem is caused by
    the presence of calcium and magnesium salts in
    the water supply (hard water). These divalent
    cations cause aggregation of the micelles, which
    then deposit as a dirty scum.

89
Washing action of soaps
90
Waxes
  • Waxes are water-repelling solids that are part
    of the protective coatings of a number of living
    things, including the leaves of plants, the fur
    of animals, and the feathers of birds. They are
    usually mixtures of esters in which both the
    alkyl and acyl group are unbranched and contain a
    dozen or more carbon atoms. Beeswax, for example,
    contains the ester triacontyl hexadecanoate as
    one component of a complex mixture of
    hydrocarbons, alcohols, and esters.

91
  • Wax is ? mixture of esters of high molecular
    weight alcohols and high molecular weight fatty
    acids.
  • Waxes are sa??infied with great difficulty than
    fats and are not attacked by lipase. Although
    waxes may be saponified by prolonged boiling with
    alcoholic KOH, they are more easily saponified by
    treating ? solution of the wax in petroleum ether
    with absolute alcohol and metallic sodium, with
    sodium ethoxide. The saponification products ?f
    waxes are water-soluble soaps (sodium Its of
    higher fatty acids) while the water insoluble
    long-chain alcohols appear in the "unsaponifiable
    matter" fraction. Waxes contain about 31 -55 of
    the unsaponifiable matter, while fats and oils
    contain only 1 - 2 unsaponifiable matter.
  • Waxes dividing on animals (spermaceti, bees wax,
    lanoline and others) and plants (carnauba wax).

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  • Bees wax. It contains esters derived from
    alcohols having 24 - 30 carbon atoms, include
    palmitate of miri??l alcohol (?30H61??) and
    n-hexacosanol (?26?53??).
  • ??3(C?2)14COOC30H61 ??3
    (C?2)14COOC26H53
  • miricyl patmitate n-
    hexacosanyl patmitate
  • Spermaceti. It is obtained from the head of the
    sperm whale. It is rich in ester of cetyl alcohol
    (?16?33??) and palmitinic acid ??3 (C ?2 )
    14COOC16H33 - cetyl palmitate
  • Spermaceti is used in making of candles.
  • Sperm Oil. It is ? liquid wax and occurs with
    spermaceti in the sperm whale. It is ? valuable
    lubricant used for delicate instruments, such as
    watches. It does not become gummy, as many oils
    do.
  • Carnauba wax. It is found in the leaves of the
    carnauba palm of Brazil. It is used as an
    ingredient in the manufacture of various wax
    polishes. Because waxes are very inert
    chemically, they make an excellent protective
    coating.
  • Lanolin or wool wax. It is obtained from wool and
    is used in making ointments and salves.

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9. Nonsaponifiable lipids
  • 1). Prostaglandins physiologically active
    substances with biogenic origin, stimulate smooth
    muscles and lowers blood pressure. All
    prostaglandins contain carboxyl group and 20
    carbon atoms in molecule, they are derivatives of
    eyicosanic acid.

94
  • Research in physiology carried out in the 1930s
    established that the lipid fraction of semen
    contains small amounts of substances that exert
    powerful effects on smooth muscle. Sheep prostate
    glands proved to be a convenient source of this
    material and yielded a mixture of structurally
    related substances referred to collectively as
    prostaglandins. We now know that prostaglandins
    are present in almost all animal tissues, where
    they carry out a variety of regulatory functions.
    Prostaglandins are extremely potent substances
    and exert their physiological effects at very
    small concentrations. Because of this, their
    isolation was difficult, and it was not until
    1960 that the first members of this class,
    designated PGE1 and PGF1, were obtained as pure
    compounds.

95
All the prostaglandins are 20-carbon carboxylic
acids and contain a cyclopentane ring. All have
hydroxyl groups at C-11 and C-15 (for the
numbering of the positions in prostaglandins).
Prostaglandins belonging to the F series have an
additional hydroxyl group at C-9, and a carbonyl
function is present at this position in the
various PGEs. The subscript numerals in their
abbreviated names indicate the number of double
bonds. Prostaglandins are believed to arise from
unsaturated C20-carboxylic acids such as
arachidonic acid. Mammals cannot biosynthesize
arachidonic acid directly.
96
  • They obtain linoleic acid from vegetable oils
    in their diet and extend the carbon chain of
    linoleic acid from 18 to 20 carbons while
    introducing two more double bonds. Linoleic acid
    is said to be an essential fatty acid, forming
    part of the dietary requirement of mammals.
    Animals fed on diets that are deficient in
    linoleic acid grow poorly and suffer a number of
    other disorders, some of which are reversed on
    feeding them vegetable oils rich in linoleic acid
    and other polyunsaturated fatty acids. One
    function of these substances is to provide the
    raw materials for prostaglandin biosynthesis.

97
  • Physiological responses to prostaglandins
    encompass a variety of effects. Some
    prostaglandins relax bronchial muscle, others
    contract it. Some stimulate uterine contractions
    and have been used to induce therapeutic
    abortions. PGE1 dilates blood vessels and lowers
    blood pressure it inhibits the aggregation of
    platelets and offers promise as a drug to reduce
    the formation of blood clots. The long-standing
    question of the mode of action of aspirin has
    been addressed in terms of its effects on
    prostaglandin biosynthesis. Prostaglandin
    biosynthesis is the bodys response to tissue
    damage and is manifested by pain and inflammation
    at the affected site. Aspirin has been shown to
    inhibit the activity of an enzyme required for
    prostaglandin formation. Aspirin reduces pain and
    inflammationand probably fever as wellby
    reducing prostaglandin levels in the body.

98
  • Much of the fundamental work on prostaglandins
    and related compounds was carried out by Sune
    Bergström and Bengt Samuelsson of the Karolinska
    Institute (Sweden) and by Sir John Vane of the
    Wellcome Foundation (Great Britain). These three
    shared the Nobel Prize for physiology or medicine
    in 1982. Bergström began his research on
    prostaglandins because he was interested in the
    oxidation of fatty acids. That research led to
    the identification of a whole new class of
    biochemical mediators. Prostaglandin research has
    now revealed that other derivatives of oxidized
    polyunsaturated fatty acids, structurally
    distinct from the prostaglandins, are also
    physiologically important. These fatty acid
    derivatives include, for example, a group of
    substances known as the leukotrienes, which have
    been implicated as mediators in immunological
    processes.

99
  • Prostaglandins have cyclopentane ring.
    According to allocation of double bonds in
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