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Carbohydrates

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Title: Carbohydrates


1
Chemistry 203
Chapter 20 Carbohydrates
2
Carbohydrates
  • Produced by photosynthesis in plants.
  • The major source of energy from our diet.
  • Composed of the elements C, H, and O.

Cn(H2O)n
Photosynthesis
6CO2 6H2O energy C6H12O6 6O2
Respiration
glucose
3
Carbohydrates
  • The most abundant organic compounds in nature
    (50 of the
  • earths biomass).
  • 3/4 of the weight of plants.
  • 1 of the weight of animals and humans (they do
    not store).
  • 65 of the foods in our diet.

4
Carbohydrates
H or enzyme
1. Monosaccharide H2O no hydrolysis
H or enzyme
2. Disaccharide H2O two monosaccharide units

H or enzyme
3. Polysaccharide many H2O many
monosaccharide units
5
Monosaccharides (Simple Sugar)
A carbohydrate that cannot be split or hydrolyzed
into smaller carbohydrates.
  • Monosaccharides are carbohydrates with
  • The simplest carbohydrates
  • 3-9 carbon atoms
  • A carbonyl group (aldehyde or ketone)
  • Several hydroxyl groups

Cn(H2O)n
CnH2nOn
C - H
H- C - OH H- C -
OH CH2OH
O
6
Monosaccharides - Aldose
O C - H aldose
H- C - OH
H- C - OH CH2OH an
aldotetrose (Erythose)
  • Aldose is monosaccharide
  • With an aldehyde group and many hydroxyl (-OH)
    groups.
  • triose (3C atoms)
  • tetrose (4C atoms)
  • pentose (5 C atoms)
  • hexose (6 C atoms)
  • Aldo- suffix

1
7
Monosaccharides - Ketose
CH2OH C
O ketose H- C - OH
H- C - OH H- C - OH
CH2OH a ketohexose
(Fructose)
1
  • Ketose is monosaccharide
  • With a ketone group and many hydroxyl (-OH)
    groups.
  • triose (3C atoms)
  • tetrose (4C atoms)
  • pentose (5 C atoms)
  • hexose (6 C atoms)
  • Keto- suffix

2
8
Monosaccharides (Simple Sugar)
  • The simplest aldose is glyceraldehyde.
  • The simplest ketose is dihydroxyacetone.

C3H6O3
C3H6O3
Constitutional Isomers
9
Some important Monosaccharides
  • Glucose (Dextrose)
  • (C6H12O6, aldohexose) Blood sugar
  • The most abundant monosaccharide
  • Is found in fruits, vegetables,
  • corn syrup, and honey.
  • Is found in disaccharides such as sucrose,
    lactose, and maltose.
  • Makes up polysaccharides such as starch,
    cellulose, and glycogen.

10
Some important Monosaccharides
Glucose (Dextrose)
- Normal blood glucose levels are 70-110 mg/dL.
- Excess glucose is stored as the polysaccharide
glycogen or as fat.
11
Some important Monosaccharides
  • Fructose
  • (C6H12O6, ketohexose),
  • Is the sweetest of the carbohydrates.
  • Is found in fruit juices and honey (fruit sugar).
  • In bloodstream, it is converted to its isomer,
    glucose.
  • Is bonded to glucose in sucrose (a disaccharide
    known as table sugar).

12
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13
Some important Monosaccharides
  • Galactose
  • (C6H12O6, aldohexose),
  • Has a similar structure to glucose except for the
    OH on Carbon 4.
  • Cannot find in the free form in nature.
  • Exist in the cellular membranes of the brain and
    nervous system.
  • Combines with glucose in lactose (a disaccharide
    and a sugar in milk).

14
Disease - Galactosemia
Galactosemia missing the enzyme that convert
galactose to glucose. Accumulation of
galactose in the blood and tissues.
Mental retardation and cataract
Solution removing the galactose from food no
milk.
15
Chirality
All carbohydrates have 1 or more chirality
centers.
Glyceraldehyde, the simplest aldose, has one
chirality center, and has two possible
enantiomers.
16
Fischer Projections
- Horizontal lines represent bonds projecting
forward from the stereocenter. - Vertical lines
represent bonds projecting to the rear. - Only
the stereocenter (tetrahedral carbon) is in the
plane.
3D
2D
17
Fischer Projections
1. Carbon with four different groups bonded to
it. 2. The chiral carbon furthest from the
carbonyl group (-CHO).








HO
H
D - glucose
L - glucose
Naturally occurring enantiomer
18
Cyclic Structure Haworth Structure
Aldehydes and ketones react with alcohols to form
hemiacetals.
Unstable
A hemiacetal contains a hydroxyl group (OH) and
an alkoxy group (OR) on the same carbon.
19
Cyclic Structure Haworth Structure
Cyclic hemiacetals form readily when the hydroxyl
and carbonyl groups are part of the same molecule.
Stable
20
Cyclic Structure Haworth Structure
1
1
Anomeric carbon
1
1
1
Alpha (a)
Beta (?)
More stable form
Anomers
21
Cyclic Structure Haworth Structure
22
Cyclic Structure Haworth Structure
?
1
1
?
?-D-Glucose ?-D-Glucose
1
1
?-D-Galactose ?-D-Galactose
23
Cyclic Structure Haworth Structure
1
Anomeric carbon
OH
CO
5
2
24
Cyclic Structure Haworth Structure
?
1
1
?
?-D-Glucose ?-D-Glucose
Humans have ?-amylase (an enzyme) and they can
digest starch products such as pasta (contain
?-glucose) Humans do not have ß-amylase (an
enzyme) and they cannot digest cellulose such as
wood or paper (contain ß-glucose)
25
Chair Conformation
?-D-Glucose (Haworth projection)
?-D-Glucose (Chair conformation)
26
Mutarotation
Change in specific rotation that accompanies the
equilibration of a and ? anomers in aqueous
solution.
36
64
lt 0.02
27
Physical properties of Monosaccharides
  • Colorless
  • Sweet Tasting
  • Crystalline solids
  • Polar with high melting points (because of OH
    groups)
  • Soluble in water and insoluble in nonpolar
    solvents
  • (H-bond because of OH groups)

28
Chemical properties of Monosaccharides
  1. Formation of Glycosides (Acetals)
  2. Oxidation
  3. Reduction

29
Formation of Glycosides (Acetals)
30
Oxidation of Monosaccharides
Aldonic acids
Reducing sugars reduce another substance.
31
Oxidation of Monosaccharides
Rearrangement (Tautomerism)
D-fructose (ketose)
D-glucose (aldose)
32
Oxidation of Monosaccharides
primary alcohol at C-6 of a hexose is oxidized to
uronic acid by an enzyme (catalyst).
Exist in connective tissue Detoxifies foreign
phenols and alcohols
33
Reduction of Monosaccharides
Alditols
Sugars alcohols sweetners in many sugar-free
(diet drinks sugarless gum).
Problem diarrhea and cataract
34
Monitoring Glucose Levels
Glucose oxidase
O2
H2O2
35
Disaccharides
  • A disaccharide
  • Consists of two monosaccharides linked by a
    glycosidic bond (when one OH group reacts with
    another OH group).
  • Glucose Glucose Maltose H2O
  • Glucose Galactose Lactose H2O
  • Glucose Fructose Sucrose H2O

36
Disaccharides
Disaccharides have at least one acetal carbon (a
carbon atom singly bonded to two OR (alkoxy)
groups.
37
Disaccharides
The glycosidic bond joining the two rings can be
alpha (a) or beta (b).
38
Disaccharides
  • Maltose
  • Is a disaccharide of two glucose molecules.
  • Has a a -1,4-glycosidic bond (between two
    a-glucoses).
  • Is obtained from the breakdown of starches.
  • Is used in cereals and candies.
  • Is a reducing sugar (carbon 1 can open to give a
    free aldehyde to oxidize).

? -1,4-glycosidic bond
?

1
4
1
4
H2O
a-glucose
a-glucose
?- maltose
39
Disaccharides
  • Lactose
  • Is a disaccharide of galactose and glucose.
  • Has a ß -1,4-glycosidic bond (between ß-galactose
    and a-gulcose).
  • Is found in milk and milk products (almost no
    sweet).
  • Is a reducing sugar (carbon 1 can open to give a
    free aldehyde to oxidize).

?
?-lactose
40
Disaccharides
  • Sucrose
  • Is found in table sugar (obtained from sugar cane
    and sugar beets).
  • Consists of glucose and fructose.
  • Has an a,ß-1,2-glycosidic bond (between a-glucose
    and ?-fructose).
  • Is not a reducing sugar (carbon 1 cannot open to
    give a free aldehyde
  • to oxidize).

ß-1,2-glycosidic bond
41
Disaccharides
Sucrose
Sucrose is very sweet, but contains many calories.
42
Artificial sweeteners
Aspartame
It (sold as Equal) is hydrolyzed
into phenylalanine, which cannot be processed
by those individuals with the condition
phenylketonuria.
43
Artificial sweeteners
Saccharine
It (sold at Sweetn Low) was used extensively
during World War I. There were concerns in the
1970s that saccharin causes cancer.
44
Artificial sweeteners
Sucralose
It (sold as Splenda) has a very similar structure
to sucrose.
45
Polysaccharides
  • Polymers of many monosaccharides units.
  • Amylose (20)
  • Starch
  • Amylopectin (80)
  • Glycogen (an energy storage in animals humans)
  • Cellulose (plant and wood structures).

(starch that stores glucose in plants such as
rice, potatoes, beans, and wheat - energy
storage).
46
Polysaccharides
  • Amylose
  • Is a polysaccharide of a-glucose in a
  • continuous (unbranched) chain (helical or
    coil
  • form).
  • Has a-1,4-glycosidic bonds between the
  • a-glucose units (250 to 4000 units).

a-1,4-glycosidic bond
47
Polysaccharides
  • Amylopectin
  • Is a polysaccharide of glucose units in branched
    chains.
  • Has a-1,4-glycosidic bonds between the a-glucose
    units.
  • Has a-1,6 bonds to branches of glucose units.
  • (at about every 25 glucose units, there is a
    branch).
  • Both forms of starch are water soluble.

48
Polysaccharides
Glycogen
- It is similar to amylopectin (more highly
branched-every 10-15 units).
- It is an energy storage molecule found in
animals/humans.
- It is stored mainly in the liver and in muscle
cells.
- When glucose is needed for energy, glucose
units are hydrolyzed from the ends of the
glycogen polymer.
- Because glycogen is highly branched, there are
many ends available for hydrolysis.
49
Polysaccharides
Amylose, Amylopectin (starch)
H or a-amylase (enzyme in saliva)
Digestion process
Dextrins (6-8 glucose units)
H or a-amylase (enzyme in pancreas)
Maltose (2 glucose units)
H or a-maltase (enzyme)
Many a-D-glucose units
50
Respiration
C6H12O6 6O2 6CO2 6H2O energy
glucose
Fermentation
Yeast
C6H12O6 2C2H5OH CO2 energy
Ethanol
51
Polysaccharides
  • Cellulose
  • Is a polysaccharide of glucose units in
    unbranched chains with b-1,4-glycosidic bonds
    (2200 glucose units).
  • Has rigid structure (H-bond) and insoluble in
    water.
  • Is the major structural material of wood plants
    (cotton 100).
  • Cannot be digested by humans because of the
  • b-1,4-glycosidic bonds (needs an enzyme
    b-glycosidase).

52
Polysaccharides
Cellulose
- Cellulose makes up the insoluble fiber in our
diets. - It passes through the digestive system
without being metabolized. - Fiber is important
in adding bulk to waste to help eliminate it more
easily (even though it gives us no nutrition).
53
Useful Carbohydrates
Amino Sugars
  • They contain an -NH2 group in place of an -OH
    group.
  • - The most abundant amino sugar in nature is
    D-glucosamine.

- Glucosamine helps keep the cartilage in joints
healthy. But natural glucosamine levels drop as
people age.
- As a supplement, glucosamine is most often used
to try to ease the joint pain caused by arthritis.
54
Useful Carbohydrates
Amino Sugars
- The second most abundant amino sugar in nature
is Chitin.
- It is a polysaccharide formed from
N-acetyl-D-glucosamine units joined together by
1,4-b-glycosidic bonds.
- Its structure is similar to cellulose
(insoluble in water).
55
Useful Carbohydrates
Glycosaminoglycans (GAGs)
They are a group of unbranched carbohydrates
derived from alternating amino sugar and
glucuronate units.
Hyaluronate extracellular fluids that lubricate
joints and in the vitreous humor of the eye.
ß-glycosidic bond
56
Useful Carbohydrates
Glycosaminoglycans (GAGs)
Chondroitin a component of cartilage and tendons.
ß-glycosidic bond
Heparin stored in the mast cells of the liver,
helps prevent blood clotting.
a-glycosidic bond
57
Useful Carbohydrates
Blood Type
- There are four blood typesA, B, AB, and O.
- Blood type is based on 3 or 4 monosaccharides
attached to a membrane protein of red blood cells.
- Each blood type has the monosaccharides below
58
Useful Carbohydrates
Blood Type
Type A blood contains a fourth monosaccharide
Type B contains an additional D-galactose unit.
Type AB has both type A and type B carbohydrates.
59
Useful Carbohydrates
Blood Type
60
Useful Carbohydrates
Blood Type
61
Useful Carbohydrates
Blood Type
- The short polysaccharide chains distinguish one
type of the red blood cell from another, and
signal the cells about the foreign viruses,
bacteria, and other agents.
- The blood of one individual may contain
antibodies to another type.
- Those with type O blood are called universal
donors, because people with any other blood type
have no antibodies to type O.
- Those with type AB blood are universal
recipients because their blood contains no
antibodies to A, B, or O.
62
Useful Carbohydrates
Blood Type
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