Chapter 18: Carbohydrates - PowerPoint PPT Presentation


Title: Chapter 18: Carbohydrates


1
Chapter 18Carbohydrates
  • 18.3 - Types of Carbohydrates
  • 18.4 and 18.6 - D and L Notations from Fischer
    Projections
  • 18.8 - Classification of Monosaccharides
  • 18.9 - Structures of Some Important
    Monosaccharides
  • 18.10 and 18.11 - Cyclic Structures of
    Monosaccharides
  • 18.12 - Chemical Properties of Monosaccharides
  • 18.13 - Disaccharides
  • 18.14 and 18.16 - Polysaccharides

2
Carbohydrates
  • Most abundant organic compounds in nature
  • Produced by photosynthesis in plants
  • Composed of the elements C, H and O
  • Also called saccharides, which means sugars
  • A major source of energy from our diet
  • A source of C for synthesis of other biomolecules
  • Can be linked to cell membranes or proteins

3
Types of Carbohydrates
  • Monosaccharides are the simplest carbohydrates
  • Empirical formula CH2O
  • Oligosaccharides contain a few monosaccharides
    (2-10)
  • Disaccharides consist of two monosaccharides
  • Polysaccharides contain many monosaccharides

4
Chiral Molecules
  • Chiral molecules
  • Have handedness
  • Nonsuperimposable on mirror images
  • Ex hand, shoe
  • Achiral molecules
  • Do not have handedness
  • Ex glass, spoon
  • Chiral molecules contain carbons with 4 different
    groups
  • Called chiral carbons or chiral center

5
Fischer Projections
  • Used to represent carbohydrates
  • Places the most oxidized group at the top
  • All chiral carbons are represented as
    intersection of lines
  • C is not shown
  • Implied 3D arrangement of atoms
  • Horizontal lines for bonds that come forward
  • Vertical lines for bonds that go back

6
D and L Notations
  • By convention, the letter L is assigned to the
    structure with the OH on the left
  • The letter D is assigned to the structure with
  • OH on the right

7
D and L Monosaccharides
  • The OH on the chiral atom farthest from the
    carbonyl group is used to assign the D or L
    configuration

8
Learning Check
  • Indicate whether each is the D or L
    isomer
  • Ribose Threose
    Fructose

9
Classification of Monosaccharides
  • Monosaccharide unbranched chain of 3-8 C atoms
    one is carbonyl, others attached to -OH
  • Aldose
  • monosaccharide with an aldehyde group (1st
    carbon)
  • Ketose
  • monosaccharide with a ketone group (2nd
    carbon)
  • Aldose Aldose
    Ketose

10
Monosaccharides
  • Monosaccharides are also classified according to
    the number of carbon atoms
  • A triose has three carbons a tetrose has four
    carbons a pentose has five carbons and a hexose
    has six carbons.
  • triose tetrose
    hexose
  • aldotriose aldotetrose
    ketohexose

11
Learning Check
  • Identify each as tetrose, pentose or hexose, and
    as aldose or ketose

A B
12
D-Glucose
  • Most common hexose
  • Found in fruits, corn syrup, and honey
  • An aldohexose with the formula C6H12O6
  • Known as blood sugar in the body
  • Building block for many disaccharides and
    polysaccharides

13
D-Galactose
  • Aldohexose
  • Differ from D-glucose at C4
  • C1 is at the top
  • Not found in the free form in nature
  • Obtained from lactose, a disaccharide (milk
    products)
  • Important in cellular membranes in CNS (brain
    sugar)

14
D-Fructose
  • Ketohexose C6H12O6
  • Differ from glucose at C1 and C2 (location of
    carbonyl)
  • The sweetest carbohydrate (2x sucrose)
  • Found in fruit juices and honey
  • Formed from hydrolysis of sucrose
  • Converts to glucose in the body

15
Learning Check
  • Draw the structure of D-fructose

16
Hemiacetal Review
  • What is a hemiacetal?
  • How is a hemiacetal formed?
  • What if the alcohol and carbonyl are attached?

17
Hexose hemiacetals
  • Favor formation of 5- or 6-membered rings
  • Hydroxyl group on C5 reacts with the aldehyde or
    ketone
  • The Haworth structure can be written from the
    Fischer projection
  • The cyclic structure of a D-isomer has the last
    CH2OH group located above the ring
  • The OH group on the left (C3) is drawn up
  • The OH groups on the right (C2, C4) are drawn
    down

18
? and ? Anomers for D-Glucose
  • Anomers are isomers which differ in placement of
    hydroxyl on C1
  • The OH is drawn down for the ?-anomer, and up
    for the ?-anomer
  • ?-D-Glucose ?-D-Glucose
  • Mashed potatoes or mashed paper?

?
?
19
Mutarotation
  • In solution, ?-D-glucose is in equilibrium with
    ß-D-glucose
  • Mutarotation involves the conversion of the
    cyclic anomers into the open chain
  • At any time, there is only a small amount of
    open chain

20
Cyclic Structure of Fructose
  • As a ketohexose, fructose forms a cyclic
    structure when the OH on C5 reacts with the
    ketone on C2
  • Result is 5-atom ring
  • Anomeric carbon is C2

?-D-Fructose
?-D-Fructose
21
Learning Check
  • Write the cyclic form of ?-D-galactose

?-D-galactose
22
ReviewReactions of aldehydes
  • Oxidation to form carboxylic acids
  • Reduction to form alcohols
  • Formation of hemiacetal
  • Hemiacetal alcohol ? acetal
  • Now well see all of these with monosaccharides

23
1. Oxidation of Monosaccharides
  • Monosaccharides are reducing sugars if their
    carbonyl groups oxidize to give carboxylic acids.
  • In the Benedicts text, D-glucose is oxidized
    to D-gluconic acid. Glucose is a reducing sugar.

24
2. Reduction of Monosaccharides
  • The reduction of the carbonyl group produces
    sugar alcohols, or alditols
  • D-Glucose is reduced to D-glucitol (also called
    sorbitol)

25
3. Monosaccharides alcohol
  • Formation of hemiacetal (cyclic structures)

26
4. Monosaccharide hemiacetals alcohol
  • When a cyclic monosaccharide reacts with an
    alcohol
  • A glycoside is produced (acetal)
  • The bond is a glycosidic bond or glycosidic
    linkage
  • ?-D-Glucose Methanol
    Methyl-?-D-glucoside

H2O
27
Learning Check
  • Write the products of the oxidation and
    reduction of D-mannose.

28
Disaccharides
  • A disaccharide consists of two monosaccharides
  • Disaccharide Monosaccharides
  • Maltose H2O Glucose Glucose
  • Lactose H2O Glucose Galactose
  • Sucrose H2O Glucose Fructose

H
29
Maltose
  • Malt sugar
  • A disaccharide in which two D-glucose molecules
    are joined by an ?-1,4-glycosidic bond
  • Obtained from starch
  • Used in cereals, candies, and brewing
  • A reducing sugar (has a hemiacetal)

30
Lactose
  • Milk sugar
  • Composed of galactose and glucose linked by a
    ?-1,4-glycosidic bond
  • Lactose intolerance
  • A reducing sugar

31
Sucrose
  • Table sugar
  • Is composed of glucose and fructose molecules
    joined by ?,?-1,2-glycosidic bond
  • Has no isomers because mutarotation is blocked
  • Not a reducing sugar (no hemiacetal)

32
Sweetness of Sweeteners
  • Sugars and artificial sweeteners differ in
    sweetness
  • Each sweetener is compared to sucrose (table
    sugar), which is assigned a value of 100

33
Learning Check
  • Identify the monosaccharides in lactose, maltose,
    and sucrose as glucose, fructose, and/or
    galactose
  • A. Lactose
  • B. Maltose
  • C. Sucrose

34
Polysaccharides
  • Polysaccharides are polymers of monosaccharides
  • Complex carbohydrates
  • Important polysaccharides of D-glucose are
  • Starch (Amylose and Amylopectin)
  • Glycogen
  • Cellulose

35
Starch and Glycogen
  • Storage polysaccharides
  • Form monosaccharides used for energy
  • Starch
  • Plants
  • Amylose is a continuous chain of glucose
    molecules linked by ?-1,4 glycosidic bonds.
  • Amylopectin is a branched chain of glucose
    molecules linked by ?-1,4- and ?-1,6-glycosidic
    bonds.
  • Glycogen
  • Humans, animals
  • Similar to amylopectin, but more highly branched.

36
Structures of Amylose and Amylopectin

37
Cellulose
  • Structural polysaccharide
  • Plant cell walls (cellulose) and animal
    exoskeletons (chitin)
  • Cellulose is a polymer of glucose molecules
    linked by ?-1,4-glycosidic bonds
  • Enzymes in saliva can hydrolyze ?-1,4-glycosidic
    bonds in starch, but not ?-1,4-glycosidic bonds
    in cellulose

38
Learning Check
  • Identify the types of glycosidic bonds in
  • 1) Amylose
  • 2) Glycogen
  • 3) Cellulose

39
End of Chapter 18!
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Chapter 18: Carbohydrates

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Title: Chapter 18: Carbohydrates


1
Chapter 18Carbohydrates
  • 18.3 - Types of Carbohydrates
  • 18.4 and 18.6 - D and L Notations from Fischer
    Projections
  • 18.8 - Classification of Monosaccharides
  • 18.9 - Structures of Some Important
    Monosaccharides
  • 18.10 and 18.11 - Cyclic Structures of
    Monosaccharides
  • 18.12 - Chemical Properties of Monosaccharides
  • 18.13 - Disaccharides
  • 18.14 and 18.16 - Polysaccharides

2
Carbohydrates
  • Most abundant organic compounds in nature
  • Produced by photosynthesis in plants
  • Composed of the elements C, H and O
  • Also called saccharides, which means sugars
  • A major source of energy from our diet
  • A source of C for synthesis of other biomolecules
  • Can be linked to cell membranes or proteins

3
Types of Carbohydrates
  • Monosaccharides are the simplest carbohydrates
  • Empirical formula CH2O
  • Oligosaccharides contain a few monosaccharides
    (2-10)
  • Disaccharides consist of two monosaccharides
  • Polysaccharides contain many monosaccharides

4
Chiral Molecules
  • Chiral molecules
  • Have handedness
  • Nonsuperimposable on mirror images
  • Ex hand, shoe
  • Achiral molecules
  • Do not have handedness
  • Ex glass, spoon
  • Chiral molecules contain carbons with 4 different
    groups
  • Called chiral carbons or chiral center

5
Fischer Projections
  • Used to represent carbohydrates
  • Places the most oxidized group at the top
  • All chiral carbons are represented as
    intersection of lines
  • C is not shown
  • Implied 3D arrangement of atoms
  • Horizontal lines for bonds that come forward
  • Vertical lines for bonds that go back

6
D and L Notations
  • By convention, the letter L is assigned to the
    structure with the OH on the left
  • The letter D is assigned to the structure with
  • OH on the right

7
D and L Monosaccharides
  • The OH on the chiral atom farthest from the
    carbonyl group is used to assign the D or L
    configuration

8
Learning Check
  • Indicate whether each is the D or L
    isomer
  • Ribose Threose
    Fructose

9
Classification of Monosaccharides
  • Monosaccharide unbranched chain of 3-8 C atoms
    one is carbonyl, others attached to -OH
  • Aldose
  • monosaccharide with an aldehyde group (1st
    carbon)
  • Ketose
  • monosaccharide with a ketone group (2nd
    carbon)
  • Aldose Aldose
    Ketose

10
Monosaccharides
  • Monosaccharides are also classified according to
    the number of carbon atoms
  • A triose has three carbons a tetrose has four
    carbons a pentose has five carbons and a hexose
    has six carbons.
  • triose tetrose
    hexose
  • aldotriose aldotetrose
    ketohexose

11
Learning Check
  • Identify each as tetrose, pentose or hexose, and
    as aldose or ketose

A B
12
D-Glucose
  • Most common hexose
  • Found in fruits, corn syrup, and honey
  • An aldohexose with the formula C6H12O6
  • Known as blood sugar in the body
  • Building block for many disaccharides and
    polysaccharides

13
D-Galactose
  • Aldohexose
  • Differ from D-glucose at C4
  • C1 is at the top
  • Not found in the free form in nature
  • Obtained from lactose, a disaccharide (milk
    products)
  • Important in cellular membranes in CNS (brain
    sugar)

14
D-Fructose
  • Ketohexose C6H12O6
  • Differ from glucose at C1 and C2 (location of
    carbonyl)
  • The sweetest carbohydrate (2x sucrose)
  • Found in fruit juices and honey
  • Formed from hydrolysis of sucrose
  • Converts to glucose in the body

15
Learning Check
  • Draw the structure of D-fructose

16
Hemiacetal Review
  • What is a hemiacetal?
  • How is a hemiacetal formed?
  • What if the alcohol and carbonyl are attached?

17
Hexose hemiacetals
  • Favor formation of 5- or 6-membered rings
  • Hydroxyl group on C5 reacts with the aldehyde or
    ketone
  • The Haworth structure can be written from the
    Fischer projection
  • The cyclic structure of a D-isomer has the last
    CH2OH group located above the ring
  • The OH group on the left (C3) is drawn up
  • The OH groups on the right (C2, C4) are drawn
    down

18
? and ? Anomers for D-Glucose
  • Anomers are isomers which differ in placement of
    hydroxyl on C1
  • The OH is drawn down for the ?-anomer, and up
    for the ?-anomer
  • ?-D-Glucose ?-D-Glucose
  • Mashed potatoes or mashed paper?

?
?
19
Mutarotation
  • In solution, ?-D-glucose is in equilibrium with
    ß-D-glucose
  • Mutarotation involves the conversion of the
    cyclic anomers into the open chain
  • At any time, there is only a small amount of
    open chain

20
Cyclic Structure of Fructose
  • As a ketohexose, fructose forms a cyclic
    structure when the OH on C5 reacts with the
    ketone on C2
  • Result is 5-atom ring
  • Anomeric carbon is C2

?-D-Fructose
?-D-Fructose
21
Learning Check
  • Write the cyclic form of ?-D-galactose

?-D-galactose
22
ReviewReactions of aldehydes
  • Oxidation to form carboxylic acids
  • Reduction to form alcohols
  • Formation of hemiacetal
  • Hemiacetal alcohol ? acetal
  • Now well see all of these with monosaccharides

23
1. Oxidation of Monosaccharides
  • Monosaccharides are reducing sugars if their
    carbonyl groups oxidize to give carboxylic acids.
  • In the Benedicts text, D-glucose is oxidized
    to D-gluconic acid. Glucose is a reducing sugar.

24
2. Reduction of Monosaccharides
  • The reduction of the carbonyl group produces
    sugar alcohols, or alditols
  • D-Glucose is reduced to D-glucitol (also called
    sorbitol)

25
3. Monosaccharides alcohol
  • Formation of hemiacetal (cyclic structures)

26
4. Monosaccharide hemiacetals alcohol
  • When a cyclic monosaccharide reacts with an
    alcohol
  • A glycoside is produced (acetal)
  • The bond is a glycosidic bond or glycosidic
    linkage
  • ?-D-Glucose Methanol
    Methyl-?-D-glucoside

H2O
27
Learning Check
  • Write the products of the oxidation and
    reduction of D-mannose.

28
Disaccharides
  • A disaccharide consists of two monosaccharides
  • Disaccharide Monosaccharides
  • Maltose H2O Glucose Glucose
  • Lactose H2O Glucose Galactose
  • Sucrose H2O Glucose Fructose

H
29
Maltose
  • Malt sugar
  • A disaccharide in which two D-glucose molecules
    are joined by an ?-1,4-glycosidic bond
  • Obtained from starch
  • Used in cereals, candies, and brewing
  • A reducing sugar (has a hemiacetal)

30
Lactose
  • Milk sugar
  • Composed of galactose and glucose linked by a
    ?-1,4-glycosidic bond
  • Lactose intolerance
  • A reducing sugar

31
Sucrose
  • Table sugar
  • Is composed of glucose and fructose molecules
    joined by ?,?-1,2-glycosidic bond
  • Has no isomers because mutarotation is blocked
  • Not a reducing sugar (no hemiacetal)

32
Sweetness of Sweeteners
  • Sugars and artificial sweeteners differ in
    sweetness
  • Each sweetener is compared to sucrose (table
    sugar), which is assigned a value of 100

33
Learning Check
  • Identify the monosaccharides in lactose, maltose,
    and sucrose as glucose, fructose, and/or
    galactose
  • A. Lactose
  • B. Maltose
  • C. Sucrose

34
Polysaccharides
  • Polysaccharides are polymers of monosaccharides
  • Complex carbohydrates
  • Important polysaccharides of D-glucose are
  • Starch (Amylose and Amylopectin)
  • Glycogen
  • Cellulose

35
Starch and Glycogen
  • Storage polysaccharides
  • Form monosaccharides used for energy
  • Starch
  • Plants
  • Amylose is a continuous chain of glucose
    molecules linked by ?-1,4 glycosidic bonds.
  • Amylopectin is a branched chain of glucose
    molecules linked by ?-1,4- and ?-1,6-glycosidic
    bonds.
  • Glycogen
  • Humans, animals
  • Similar to amylopectin, but more highly branched.

36
Structures of Amylose and Amylopectin

37
Cellulose
  • Structural polysaccharide
  • Plant cell walls (cellulose) and animal
    exoskeletons (chitin)
  • Cellulose is a polymer of glucose molecules
    linked by ?-1,4-glycosidic bonds
  • Enzymes in saliva can hydrolyze ?-1,4-glycosidic
    bonds in starch, but not ?-1,4-glycosidic bonds
    in cellulose

38
Learning Check
  • Identify the types of glycosidic bonds in
  • 1) Amylose
  • 2) Glycogen
  • 3) Cellulose

39
End of Chapter 18!
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