carbohydrates for ug

The Structure and

Function ofMacromolecules(Carbohydrates)

Important Point:

Polymers / Monomers

Many macromolecules consist of polymers A polymer is a large molecule built up from smaller

building block molecules Monomers (a.k.a., subunits) are the building block

molecules Small molecules common to all organisms are ordered

into unique macromolecules . . . For each class (of compound) we will see that the macromolecules have emergent properties not found in their individual monomers.”

Polymers, Monomers, and Lipids

polymercategory of

biomoleculesmonomer

polysaccharide carbohydrates monosaccharides

polypeptides proteins amino acids

polynucleic acids RNA & DNA nucleotides

5

Chapter Carbohydrates

I (CH2O)n or H - C - OH

I

Carbohydrates have the following basic composition:

the term carbohydrate is derived from the french: hydrate de carbone

6

Carbohydrates

Carbohydrates are The hydrates of carbon Carbohydrates often written as “COH” Basic chemical structure consists of

sugar units Found as aldehydes or ketones

derived from polyhydric alcohols A major source of energy from our

diet. Composed of the elements C, H, and

O.

SARKARA (Sanskrit), SAKCHARON (Greek), SACCHARUM (Latin)

7

Carbohydrates

Carbohydrates Also called saccharides, which means

“sugars.” often shown as aliphatic or linear

structures, but exist in nature as ringed structures

Are produced by photosynthesis in plants.

Such as glucose are synthesized in plants from CO2, H2O, and energy from the sun.

Are oxidized in living cells (respiration) to produce CO2, H2O, and energy.

What Do Carbohydrates Do?

Carbohydrates are important building blocks in the synthesis of other molecules.

They indicate cell identity. (Glycocalyx on cells) They store chemical energy. (Glycogen and starch) They provide cells with fibrous structural materials.

(Example: cellulose in plants) Intermediates in the biosynthesis of other basic

biochemical entities (fats and proteins) Associated with other entities such as glycosides,

vitamins and antibiotics) Participate in biological transport, cell-cell recognition,

activation of growth factors, modulation of the immune system

8

9

Types of Carbohydrates

The types of carbohydrates are (Usually by the number of sugar units in the molecule)

Monosaccharides - simple sugars with multiple OH groups. Based on number of carbons (3, 4, 5, 6), a monosaccharide is a triose, tetrose, pentose or hexose.

Disaccharides - 2 monosaccharides covalently linked.

Oligosaccharides - a few monosaccharides covalently linked.

Polysaccharides (Glycans) - polymers consisting of chains of monosaccharide or disaccharide units.

10

Monosaccharides

Monosaccharides (simple sugars) cannot be broken down into simpler sugars under mild conditions, are consist of

3 to 6 carbon atoms, typically. A carbonyl group (aldehyde or ketone). Several hydroxyl groups. Aldoses and ketoses contain aldehyde and ketone functions,

respectively. Triose, tetrose, etc. Denotes number of carbons. Aldoses with 3c or more and ketoses with 4c or more are chiral. Most (99%) are straight chain compounds D-glyceraldehyde is the simplest of the aldoses (aldotriose) All other sugars have the ending ose (glucose, galactose,

ribose, lactose, etc…)

Monosaccharides Vary in Structure

11

(1) Location of the carbonyl group. Aldose: The carbonyl is at the end of the monosaccharide. Ketose: The carbonyl is in the middle of the sugar’s carbon

chain.

(2) Number of carbon atoms present. Triose: three Pentose: five Hexose: six

(3) Spatial arrangement of their atoms. Different arrangement of the hydroxyl groups.

Monosaccharides Nomenclature

12

Ketone Aldehyde

4 Tetrose Tetrulose

5 Pentose Pentulose

6 Hexose Hexulose

7 Heptose Heptulose

8 Octose Octulose

Nu

mb

er o

f ca

rbo

ns

Functional group

13

Aldoses

Aldoses are monosaccharides With an aldehyde group at

the end. With many hydroxyl (─OH)

groups.

triose (3 C atoms)

tetrose (4 C atoms)

pentose (5 C atoms)

hexose (6 C atoms)

O ║

C─H aldose │ H─ C─OH │ H─ C─OH │

CH2OH

Erythose, an aldotetrose

C

C

CH2OH

OH)n(H

O

H

Aldose

C

C

CH2OH

OHH

O

H

Aldotriosen = 1

C

CH2OH

OHH

C O

H

C OHH

Aldotetrosen = 2

C

CH2OH

OHH

C O

H

C OHH

C OHH

Aldopentose n = 3

C O

H

C OHH

C OHH

CH OH

C

CH2OH

OHH

Aldohexose n = 4

Aldose sugars

16

Ketoses

Ketoses are monosaccharides With a ketone group,

usually at C2. With many hydroxyl (─OH)

groups.

triose (3 C atoms)

tetrose (4 C atoms)

pentose (5 C atoms)

hexose (6 C atoms)

CH2OH │ C=O ketose │ H─ C─OH │ H─ C─OH │

H─C─OH │

CH2OH

Fructose, a ketohexose

C

C

CH2OH

OH)n(H

O

CH2OH

Ketose

CH2OH

C O

CH2OH

Ketotriose n = 0

CH2OH

C O

C OHH

CH2OH

Ketotetrose n = 1

C OHH

CH2OH

CH2OH

C O

C OHH

Ketopentose n = 2

C OHH

CH2OH

CH2OH

C O

C OHH

OHH

Ketohexose n = 3

Ketose sugars

19

Learning Check

Identify each as aldo- or keto- and as tetrose, pentose,

or hexose:

A B

H

CH2OH

OHC

H

H

H

OH

OH

OH

C

C

C

HC

O

CH2OH

HHO

CH2OH

O

H OHC

C

C

20

Solution

A. aldohexose

B. ketopentose

21


Structures of Monosaccharides

Fisher projection: straight chain representation Haworth projection: simple ring in perspective Conformational representation: chair and boat

configurations

So

me

Mo

no

sacc

har

ides

Note Basic Formula: (CH2O)n

Hence: “Carbo” (C) “Hydrate” (H2O)

So

me

Mo

no

sacc

har

ides

All carbons in a monosaccharide are bonded to a hydroxyl group (-OH) except for one which is bonded to a carbonyl group (=O) (note that this statement is true only

for the linear form of monosaccharides)

Chiral Carbons

A carbon is chiral if it has four different groups Chiral compounds have the same composition but

are not superimposable Display in Fisher projection

CH2OH

H OH

CHO

CH2OH

OH H

CHO

D-glyceraldehyde L-glyceraldehyde

ENANTIOMERS

So

me

Mo

no

sacc

har

ides

Th

e tw

o s

imp

lest

su

gar

s 2 |1—C—3 | 4

2 |3—C—1 | 4

Note Numerous Chiral Carbons

Carbonyl Group Configurations

26

Carbonylgroup atend of carbonchain

An aldose A ketose

Carbonylgroup inmiddle of carbonchain

27

Fischer Projections

A Fischer projection Is used to represent carbohydrates. Places the most oxidized group at the top. Shows chiral carbons as the intersection of vertical

and horizontal lines.

28

D and L Notations

For sugars with more than one chiral center, in a Fischer projection, the −OH group on the

Chiral carbon farthest from the carbonyl group determines an L or D isomer.

Left is assigned the letter L for the L-isomer. Right is assigned the letter D for the D-isomer.

D & L designations are based on the configuration about the single asymmetric C in glyceraldehyde.

29

D & L sugars are mirror images of one another.

They have the same name, e.g., D-glucose & L-glucose.

Other stereoisomers have unique names, e.g., glucose, mannose, galactose, etc.

Vant Hoff’s Rule: The number of stereoisomers is 2n, where n is the number of asymmetric centers.

The 6-C aldoses have 4 asymmetric centers. Thus there are 16 stereoisomers (8 D-sugars and 8 L-sugars).

O H O H C C H – C – OH HO – C – H

HO – C – H H – C – OH

H – C – OH HO – C – H

H – C – OH HO – C – H

CH2OH CH2OH

D-glucose L-glucose

D and L Notations

30

Examples of D and L Isomers of Monosaccharides

O

CH2OH

H OH

H OH

HO H

OHH

C H

CH2OH

H OH

H OH

OHH

HC

OH

O

CH2OH

HO H

H OH

H OH

HHO

C

D-glucose D-ribose L-galactose

31

Learning Check

Identify each as the D or L isomer.

A. B. C.

__-ribose __- threose __- fructose

CH2OH

HO H

HO H

HHO

O

C H

CH2OH

HO H

OHH

O

C H

CH2OH

H OH

H OH

HO H

O

CH2OH

32

Solution

Identify each as the D or L isomer. A. B. C.

L-ribose L-threose D-fructose

CH2OH

HO H

HO H

HHO

O

C H

CH2OH

HO H

OHH

O

C H

CH2OH

H OH

H OH

HO H

O

CH2OH

More Stereochemistry

Know these definitions Stereoisomers that are mirror images of each other

are enantiomers. Pairs of isomers that have opposite configurations at

one or more chiral centers but are NOT mirror images are diastereomers.

Two sugars that differ in configuration at only one chiral center are epimers.

D-mannose and D-glucose are C-2 epimers.

D-galactose and D-glucosea re C-4 epimers

33

Epimers

34

CHO

H OH

H OH

CH2OH

H OH

CHO

HO H

H OH

CH2OH

H OH

D-ribose D-arabinose

C-2 epimers

CHO

OHH

HHO

OHH

OHH

CH2OH

D-glucose

CHO

HHO

HHO

OHH

OHH

CH2OH

D-mannose

CHO

OHH

HHO

HHO

OHH

CH2OH

D-galactose

Varying Configurations of Hydroxyl Groups

35

Differentconfiguration

of hydroxyl groups

Glucose Galactose

36

D-Glucose (Dextrose) – Blood Sugar

D-glucose is Most common

carbohydrate Found in fruits, corn

syrup, and honey. An aldohexose with the

formula C6H12O6.

Rotate the polarized light to the right.

The monosaccharide in polymers of starch, cellulose, and glycogen.

37

D-Fructose (Levulose) – Fruit Sugar

D-fructose Is a ketohexose

C6H12O6.

Rotate polarized light to the left.

Is the sweetest carbohydrate.

Is found in fruit juices and honey.

Converts to glucose in the body.

H OH

CH2OH

C

HO

H OH

H

C

O

C

C

CH2OH

D-Fructose

38

D-Galactose

D-galactose is

An aldohexose C6H12O6.

Not found free in nature. Obtained from lactose, a

disaccharide. A similar structure to

glucose except for the

–OH on C4.

H

H

H OH

CH2OH

C

HO

HO HC

OH

C

C

O

C H

D-Galactose

39

Learning Check

Draw the structure and Fischer projection of D-fructose.

40

Solution

CH2OH│C=O

HO H

H OH

H OH

CH2OH

Fischer projection

H OH

CH2OH

C

HO

H OH

H

C

O

C

C

CH2OH

D-Fructose

41


Cyclic Structures of Monosaccharides

OH

OH

OHOH

CH2OH

O

O O

PYRAN FURAN

Hemiacetal & hemiketal formation

An aldehyde can react with an alcohol to form a hemiacetal.

A ketone can react with an alcohol to form a hemiketal.

Cyclic form of glucose is mainly a pyranose. Cyclic form of fructose is mainly a furanose.

O C

H

R

OH

O C

R

R'

OHC

R

R'

O

aldehyde alcohol hemiacetal

ketone alcohol hemiketal

C

H

R

O R'R' OH

"R OH "R

+

+

Anomeric Carbon --- The carbon atom which is involved in hemiacetal or acetal formation.

Pentoses and hexoses can cyclize as the ketone or aldehyde reacts with a distal OH.

Glucose forms an intra-molecular hemiacetal, as the C1 aldehyde & C5 OH react, to form a 6-member pyranose ring, named after pyran.

These representations of the cyclic sugars are called Haworth projections.

H O

OH

H

OHH

OH

CH2OH

H

OH

H H O

OH

H

OHH

OH

CH2OH

H

H

OH

-D-glucose -D-glucose

23

4

5

6

1 1

6

5

4

3 2

H

CHO

C OH

C HHO

C OHH

C OHH

CH2OH

1

5

2

3

4

6

D-glucose (linear form)

Cyclic Structures

Fructose forms either a 6-member pyranose ring, by reaction of the C2 keto

group with the OH on C6, or a 5-member furanose ring, by reaction of the C2 keto

group with the OH on C5. CH2OH

C O

C HHO

C OHH

C OHH

CH2OH

HOH2C

OH

CH2OH

HOH H

H HO

O

1

6

5

4

3

2

6

5

4 3

2

1

D-fructose (linear) -D-fructofuranose

Cyclic Structures

Anomers

Anomers are two sugars that differ in configuration only at the ‘C’ that was the carbonyl carbon in the open chain form.

‘Ano’ gr: for “upper” Anomers like epimers are a kind of diastereomers.

45

Cyclization of glucose produces a new asymmetric center at C1. The 2 stereoisomers are called anomers, α & β.

Haworth projections represent the cyclic sugars as having essentially planar rings, with the OH at the anomeric C1:

For D-sugars, has OH down, has OH up.

For L-sugars, the reverse is true.

H O

OH

H

OHH

OH

CH2OH

H

-D-glucose

OH

H H O

OH

H

OHH

OH

CH2OH

H

H

OH

-D-glucose

23

4

5

6

1 1

6

5

4

3 2

Cyclic Structures

Optical Isomerism

A property exhibited by any compound whose mirror images are non-superimposable

Asymmetric compounds rotate plane polarized light Enantiomers - Optical isomers rotate the beam of

plane-polarized light for the same angle, but in opposite direction

Rotation is either (+) dextrorotatory or (-) levorotatory Equimolar mixture of optical isomers has no optical

activity - racemic mixture Measurement of optical activity in chiral or asymmetric

molecules using plane polarized light Molecules may be chiral because of certain atoms or

because of chiral axes or chiral planes48

Mutarotation

Process by which various anomeric forms attain an

equilibrium in solution

Change in optical activity of a optically active compound

in solution.

The optical rotation of glucose solution could change with

time. It involves interconversion of - and -D-glucose.

[]D20 = 112.2 for -D-glucose

[]D20 = 18.7 for -D-glucose

α - D - glucose -> D – glucose <- β - D – glucose

α20D = 113 α20

D = 52 α20D = 19

At equilibrium = 35% of α - form and 65% of β - form. 49

Mutarotation

50

~37%

0.0026%

<<1%

~63%

Because of the tetrahedral nature of carbon bonds, pyranose sugars actually assume a "chair" or "boat" configuration, depending on the sugar.

The representation above reflects the chair configuration of the glucopyranose ring more accurately than the Haworth projection.

O

H

HO

H

HO

H

OH

OHHH

OH

O

H

HO

H

HO

H

H

OHHOH

OH

-D-glucopyranose -D-glucopyranose

1

6

5

4

32

Cyclic Structures

52

Cyclic Structures

Cyclic structures Are the prevalent form of monosaccharides with 5 or

6 carbon atoms.

Form when the hydroxyl group on C-5 reacts with the aldehyde group or ketone group.

O O

53

Cyclic Haworth Structures

Stable cyclic hemiacetals form When the C=O group and the

—OH are part of the same molecule.

For hexoses, the hydroxyl group on C-5 reacts with the aldehyde group or ketone group.

The cyclic structure of a D-isomer has the last CH2OH group located above the ring.

CH2OH

O

Rules for drawing Haworth projections Draw either a six or 5-membered ring including

oxygen as one atom

Most aldohexoses are six-membered Aldotetroses, aldopentoses, ketohexoses are 5-

membered

O O

Rules for drawing Haworth projections

Next number the ring clockwise starting next to the oxygen

If the substituent is to the right in the fisher projection, it will be drawn down in the haworth projection (down-right rule)

O O

1

23

4

5

1

23

4

Rules for drawing Haworth projections For D-sugars the highest numbered carbon (furthest

from the carbonyl) is drawn up. For L-sugars, it is drawn down

For D-sugars, the OH group at the anomeric position is drawn down for and up for . For L-sugars is up and is down

57

Drawing the Cyclic Structure for Glucose

STEP 1 Number the carbon chain and turn clockwise to form a linear open chain.

HHO

H

CH2OH

OHC

H

H

OH

OH

C

C

C

OH

C1

2

3

4

5

6

6 5 4 3 2 1

H

OHH

OH

C

H H

OH OH

C C CH

O

CHOCH2

58

Cyclic Structure for Glucose

STEP 2 Bend the chain to make a hexagon

Bond the C5 –O– to C1. Place the C6 group above

the ring. Write the –OH groups on

C2 and C4 below the ring. Write the –OH group on C3

above the ring. Write a new –OH on C1.

6 5

4 1

3 2 OH

OH

OHOH

CH2OH

O

59

Cyclic Structure for Glucose (cont)

-D-glucose -D-glucose

STEP 3 The new –OH on C1 is drawn Down for the anomer. Up for the anomer.

OCH2OH

OHOH

OH

OH

OCH2OH

OHOH

OH

OH

60

Summary of the Formation of Cyclic Glucose

These are all Glucose Memorize this structure

Linear and Ring Forms

61

Linear form of glucose Ring forms of glucose

-Glucose

-Glucose

Oxygen from the5-carbon bonds to the1-carbon, resulting in a ring structure

62

-D-Glucose and β-D-Glucose in SolutionWhen placed in solution, Cyclic structures open and close. -D-glucose converts to β-D-glucose and back. There is only a small amount of open chain.

-D-glucose D-glucose (open) β-D-glucose (36%) (trace) (64%)

OH

OH

OHOH

CH2OH

OOH

OH

OHOH

CH2OH

OOH

CH2OH

OH

OC

H

OH

OH

63

Cyclic Structure of Fructose

Fructose Is a ketohexose. Forms a cyclic structure. Reacts the —OH on C-5 with the C=O on C-2.

D-fructose -D-fructoseα-D-fructose

O CH2OH

OH

OH

OH

CH2OH

O OH

CH2OH

OH

OH

CH2OH

H OH

H OH

HHO

O

CH2OH

C

C

C

C

CH2OH

64

Learning Check

Write the cyclic form of -D-galactose

H

H

H OH

CH2OH

C

HO

HO HC

OH

C

C

O

C H

65

Solution

-D-galactose

OH

OH

OH

OH

CH2OH

O

Saccharides Isomerism - Review

STRUCTURE isomerism (constitutional) same summary formula, different functional groups aldose ketose glucose fructose

OPTICAL isomerism (antipods, enantiomers) D- and L- isomerism mirror images D-glucose L-glucose

EPIMERISM different orientation of hydroxyl on one C ( not reference) glucose manose glucose galactose

PYRANOSE-FURANOSE-ACYKLIC FORM α-D-glucopyranose β-D-glucofuranose acyclic glucose

ANOMERISM α-D-glucopyranose β-D-glucopyranose mutarotation

67


Chemical Properties of

Monosaccharides

68

Reducing Sugars

Are monosaccharides with a carbonyl group that oxidizes to give a carboxylic acid.

Sugars with free anomeric carbons Undergo reaction with benedict’s reagent (cu2+) to

give the corresponding carboxylic acid.

Fehling’s reagent: CuSO4 (blue) + RC(=O)H Cu2O (red) + RCO2-

Tollen’s reagent: Ag+ Ag0 Include the monosaccharides glucose, galactose,

and fructose.

69

Oxidation of D-Glucose

+ Cu2O(s)

D-gluconic acidD-glucose

+ Cu2+

H OH

H OH

HHO

H OH

O

OH

CH2OH

C

C

C

C

C

H OH

H OH

HHO

H OH

O

H

CH2OH

C

C

C

C

C

[O]

Benedicts reagent

Glucose is a reducing sugar

Cu+ (reduced form)

Glucose is oxidized to a carboxylic acid

70

Reduction of Monosaccharides

The reduction of monosaccharides

Involves the carbonyl group.

Produces sugar alcohols called alditols.

Such as D-glucose gives D-glucitol also called sorbitol.

D-Glucitol

71

Learning Check

Write the products of the oxidation and reduction of

D-mannose.

H

O

CH2OH

H OH

H OH

HO H

HHO

C

D-mannose

72

Solution

Write the products of the oxidation and reduction of

D-mannose.

H

O

CH2OH

H OH

H OH

HO H

HHO

C OH

O

CH2OH

H OH

H OH

HO H

HHO

C

CH2OH

H OH

H OH

HO H

HHO

CH2OH

Reduction Oxidation

D-mannitol D-mannose D-mannonic acid

73


Sugar Derivatives

Sugar derivatives

sugar alcohol (alditols) - lacks an aldehyde or ketone; e.g., ribitol.

sugar acid - the aldehyde at C1, or OH at C6, is oxidized to a carboxylic acid; e.g., gluconic acid, glucuronic acid.

CH2OH

C

C

C

CH2OH

H OH

H OH

H OH

D-ribitol

COOH

C

C

C

C

H OH

HO H

H OH

D-gluconic acid D-glucuronic acid

CH2OH

OHH

CHO

C

C

C

C

H OH

HO H

H OH

COOH

OHH

amino sugar - an amino group substitutes for a hydroxyl. An example is glucosamine.

The amino group may be acetylated, as in N-acetylglucosamine.

H O

OH

H

OH

H

NH2H

OH

CH2OH

H

-D-glucosamine

H O

OH

H

OH

H

NH

OH

CH2OH

H

-D-N-acetylglucosamine

C CH3

O

H

Sugar derivatives

N-acetylneuraminate (N-acetylneuraminic acid, also called sialic acid) is often found as a terminal residue of oligosaccharide chains of glycoproteins.

Sialic acid imparts negative charge to glycoproteins, because its carboxyl group tends to dissociate a proton at physiological pH, as shown here.

NH O

H

COO

OH

H

HOH

H

H

RCH3C

O

HC

HC

CH2OH

OH

OH

N-acetylneuraminate (sialic acid)

R =

Sugar derivatives

Deoxy sugars: These are monosaccharides which lack one or more hydroxyl groups on the molecule; example: 2’-deoxy ribose - constituents of DNA, 6-deoxy-L-mannose (L-rhamnose) is used as a fermentative reagent in bacteriology, etc.

Sugar esters: phosphate esters like ATP are important. Acetals, ketals and glycosides: basis for oligo- and poly-saccharides.

77

Sugar derivatives

78


Glycosidic Bonds

Glycosidic Bonds

The anomeric hydroxyl and a hydroxyl of another sugar or some other compound can join together, splitting out water to form a glycosidic bond:

R-OH + HO-R' R-O-R' + H2O

E.g., methanol reacts with the anomeric OH on glucose to form methyl glucoside (methyl-glucopyranose).

O

H

HO

H

HO

H

OH

OHHH

OH

-D-glucopyranose

O

H

HO

H

HO

H

OCH3

OHHH

OH

methyl- -D-glucopyranose

CH 3-O H+

methanol

H2O

with hemiacetal hydroxyl of other saccharide

nonreducing disaccharides with other then hemiacetal hydroxyl of other saccharide

reducing disaccharides with nonsugar hydroxyl (alcohol, sterol, heterocycle)

O-glycosides with amino(imino) group

N-glycosides

80

Glycosidic Bonds

When an anomeric carbon participates in a glycosidic bond, it cannot be oxidized by ferric or cupric ion.

The sugar containing that anomeric carbon cannot exist in linear form and can no longer act as a reducing sugar.

reducing end: the end of a chain with a free anomeric carbon

81

Glycosidic Bonds

82


Disaccharides

83

Important Disaccharides

A disaccharide Consists of two monosaccharides. 2 sugars joined by a condensation reaction to form a

glycosidic bond

Monosaccharides Disaccharide

Glucose + glucose maltose + H2O

Glucose + galactose lactose + H2OGlucose + fructose sucrose + H2O

84

Maltose (Malt Sugar)

Maltose is Composed of two D-glucose molecules. Obtained from the hydrolysis of starch. Linked by an -1,4-glycosidic bond formed from the

−OH on C1 of the first glucose and −OH on C4 of the second glucose.

Used in cereals, candies, and brewing. Found in both the - and β - forms. Reducing sugar Shows mutarotation Its full name is -D-glucopyranosyl-(14)--D-

glucopyranose

85

Formation of Maltose

Reducing end

86

Cellobiose

Cellobiose is A disaccharide Composed of two D-glucose molecules. Obtained from the hydrolysis of cellulose. Linked by an -1,4-glycosidic bond formed from the −OH

on C1 of the first glucose and −OH on C4 of the second glucose.

The -1,4-glycosidic linkage is represented as a zig-zag, but one glucose is actually flipped over relative to the other.

Reducing sugar Shows mutarotation Its full name is -D-glucopyranosyl-(14)--D-

glucopyranose

Formation Of Cellobiose

H O

O H

H

O HH

O H

CH 2O H

H

O O H

H

H

O HH

O H

CH 2O H

H

H

H

O1

23

4

5

6

1

23

4

5

6

cellobiose

Reducing end

88

Lactose (Milk Sugar)

Lactose Is a disaccharide of β-d-galactose and α- or β-d-

glucose. Contains a β -1,4-glycosidic bond. Is found in milk and milk products. Reducing sugar Shows mutarotation Its full name is b-d-galactopyranosyl-(14)-a-d-

glucopyranose Used in infant formulations, medium for penicillin

production and as a diluent in pharmaceuticals

Formation of Lactose

Reducing end

90

Sucrose (Table Sugar)

Is obtained from sugar cane and sugar beets. Consists of α-d-glucose and β-d-fructose.. Has an α,β-1,2-glycosidic bond. Non-reducing sugar Do not show mutarotation The full name of sucrose is a-d-glucopyranosyl-(12)-

b-d-fructopyranose. Invert sugar --- when sucrose in solution, the rotation

changes from detrorotatory (+66.5) to levorotatory (-19.8). So, sucrose is called “invert sugar”.

Used pharmaceutically to make syrups, troches

Formation of Sucrose

92

Formation of Sucrose

Note that Fruhas been flipped

and that it is in the-position

Trehalose

Trehalose is a disaccharide that occurs naturally in insects, plants, fungi, and bacteria.

The major dietary source is mushrooms. Trehalose is used in bakery goods, beverages,

confectionery, fruit jam, breakfast cereals, rice, and noodles as a texturizer, stabilizer, humectant, or formulation aid with a low sweetening intensity

93

O

CH2OH

H

O O

H

H

H

HO

H

OH

OH

H

OH H

H

OH

OH

H

HOH2C

TREHALOSE

94

Learning Check

Write the structures and names of the two monosaccharides that form when sucrose is hydrolyzed.

95

Solution

α-D-glucose

β-D-fructose

96

Learning Check

Identify the monosaccharides in each of the following:

A. lactose

(1) α-D-glucose (2) β-D-fructose (3) β-D-galactose

B. maltose


C. sucrose


97

Solution

Identify the monosaccharides in each of the following:

A. lactose

(1) α-D-glucose (3) β-D-galactose

B. maltose

(1) α-D-glucose

C. sucrose

(1) α-D-glucose (2) β-D-fructose

99


Oligosaccharides

Raffinose

(Galactose + Glucose + Fructose)

6-0--D-Galactopyranosyl (1->6)-2-0--D-Glucopyranosyl (1->2)--D-Fructofuranoside

100

O

OH

OH

CH2OH

OH

CH2OHO

OH

OH

O

OH

CH2OH

O

HO

OH

CH2

O

Melbiose Sucrose Moiety

Stachyose

(Galactose + Galactose + Glucose + Fructose)

6-0-a-D-Galactopyranosyl (1->6)-6-0-a-D-Galactopyranosyl (1-> 6) -2-0-a-D-Glucopyranosyl-b-D-Fructofuranoside

“Flatulence Factor”

101

O

OH

OH

CH2OH

OH

CH2OH

O

OH

OH

OH

OH

CH2OH

O

HO

OH

CH2

O

O

O

OH

OH

CH2

O

102


Polysaccharides

103

Polysaccharides

Polysaccharides

Polysaccharides are polymers that form from monosaccharides through a condensation reaction between two hydroxyl groups to create a glycosidic linkage.

(1) The monomers joined by glycosidic linkages can be identical or different.

(2) The glycosidic linkages can form between any two hydroxyl groups; so the location and geometry of these bonds vary widely.

characteristics: polymers (MW from 200,000) White and amorphous products (glassy) not sweet not reducing; do not give the typical aldose or ketose

reactions) form colloidal solutions or suspensions

104

Polysaccharides

Functions: storage, structure, recognition Nomenclature: homopolysaccharide vs.

heteropolysaccharide. Lower the osmotic pressure. Starch and glycogen are energy storage molecules. Chitin and cellulose are structural molecules. Cell surface polysaccharides are recognition

molecules.

105

Polysaccharides

Plants store glucose as amylose or amylopectin, glucose polymers collectively called starch.

Most starch is 10-30% amylose and 70-90% amylopectin.

Glucose storage in polymeric form minimizes osmotic effects.

The end of the polysaccharide with an anomeric C1 not involved in a glycosidic bond is called the reducing end.

Starch is used as an excipient, a binder in medications to aid the formation of tablets.

Industrially it has many applications such as in adhesives, paper making, biofuel, textiles. 106

Starch

107

Structures of Amylose and Amylopectin

108

Amylose

Amylose is A polymer of α-d-glucose

molecules. Linked by -1,4 glycosidic

bonds. A continuous (unbranched)

chain.

• 200 to 20 000 glucose units • helix

109

Amylopectin

Amylopectin Is a polymer of α-D-glucose

molecules. Is a branched-chain

polysaccharide. Has α-1,4-glycosidic bonds

between the glucose units. Has α-1,6 bonds to

branches in every 12-30 residues.

The branches produce a compact structure & provide multiple chain ends at which enzymatic cleavage can occur.

Starch

Amylose and amylopectin are poorly soluble in water, but form micellar suspensions.

In these suspensions, amylose is helical and iodine fits into the helices to produce a blue color. Amylopectin produces a red-violet color with I2.

Branches provide a mechanism for quickly releasing (or storing) glucose units for (or from) metabolism. 110

111

Glycogen

Glycogen Is the polysaccharide that stores α-D-

glucose in muscle, the glucose storage polymer in animals.

Is similar to amylopectin, but is more highly branched.

Glycogen constitutes up to 10% of liver mass and 1-2% of muscle mass.

Glycogen is stored energy for the organism.

(1,6) branches every 8-12 residues . Like amylopectin, glycogen gives a red-

violet color with iodine.

112

Glycogen

H O

OH

H

OHH

OH

CH 2OH

HO H

H

OHH

OH

CH 2OH

H

O

HH H O

OH

OHH

OH

CH 2

HH H O

H

OHH

OH

CH 2OH

H

OH

HH O

OH

OHH

OH

CH 2OH

H

O

H

O

1 4

6

H O

H

OHH

OH

CH 2OH

HH H O

H

OHH

OH

CH 2OH

HH

O1

OH

3

4

5

2

glycogen

The highly branched structure permits rapid glucose release from glycogen stores, e.g., in muscle during exercise.

The ability to rapidly mobilize glucose is more essential to animals than to plants.

more branching

carbon and energy (glucose) storage molecules

Dextrans

A small but significant difference from starch and glycogen.

If you change the main linkages between glucose from (1,4) to (1,6), you get a new family of polysaccharides – dextrans.

Branches can be (1,2), (1,3), or (1,4). Dextrans formed by bacteria are components of

dental plaque. Cross-linked dextrans are used as "Sephadex" gels in

column chromatography. used as plasma extenders (treatment of shock) These gels are up to 98% water!

114

Structural Polysaccharides

Composition similar to storage polysaccharides, but small structural differences greatly influence properties.

Cellulose is the most abundant natural polymer on earth.

Cellulose is the principal strength and support of trees and plants .

Cellulose can also be soft and fuzzy - in cotton.

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Other Structural Polysaccharides

Chitin - exoskeletons of crustaceans, insects and spiders, and cell walls of fungi. similar to cellulose, but C-2s are N-acetyl cellulose strands are parallel, chitins can be

parallel or antiparallel. Alginates – Ca2+-binding polymers in algae. Agarose and agaropectin - galactose polymers Glycosaminoglycans - repeating disaccharides with

amino sugars and negative charges.

116

117

Cellulose

Cellulose Is a polysaccharide of glucose units in unbranched

chains. Has β-1,4-glycosidic bonds. Cannot be digested by humans because humans

cannot break down β-1,4-glycosidic bonds.

Gives no color with iodine. A structural polysaccharide Yields glucose upon complete hydrolysis Partial hydrolysis yields cellobiose

118

Cellulose

Every other glucose is flipped over, due to β linkages. This promotes intra-chain and inter-chain H-bonds and van der

Waals interactions, that cause cellulose chains to be straight & rigid, and pack with a crystalline arrangement in thick bundles - microfibrils.

Multisubunit Cellulose Synthase complexes in the plasma membrane spin out from the cell surface microfibrils consisting of 36 parallel, interacting cellulose chains.

These microfibrils are very strong. The role of cellulose is to impart strength and rigidity to plant cell

walls, which can withstand high hydrostatic pressure gradients. Osmotic swelling is prevented.

119

Cellulose

Schematic of arrangement of cellulose chains in a microfibril.

Cel

lulo

se

Know the difference

Cel

lulo

se

Cellulose is a Structural

polysaccharide

Cel

lulo

seMost organisms

cannot digest (hydrolyze) cellulose

Organisms that can digest cellulose include the microorganisms living the gastrointestinal tract of many organisms typified especially by cows and termites and many fungi (i.e., the things that “eat” the wood of fallen trees)

Chitin

Chitin is the second most abundant carbohydrate polymer

Like cellulose, chitin is a structural polymer Present in the cell wall of fungi and in the

exoskeletons of crustaceans, insects and spiders Chitin is used commercially in coatings (extends the

shelf life of fruits and meats) A chitin derivative binds to iron atoms in meat and

slows the rancidity process

123

124

Chitin

125

Learning Check

Identify the polysaccharides and types of glycosidic

bonds in each of the following:

A. B. C.

126

Solution

A. Cellulose -1,4-glycosidic bonds

B. Amylose -1,4-glycosidic bonds

Amylopectin -1,4-and -1,6-glycosidic bonds

C. Glycogen -1,4-and -1,6-glycosidic bonds

(more branched than amylopectin)

Polysaccharides: Branched and Unbranched

127

128


Glycosaminoglycans (mucopolysaccharides) are linear polymers of repeating disaccharides.

The constituent monosaccharides tend to be modified, with acidic groups, amino groups, sulfated hydroxyl and amino groups, etc.

Glycosaminoglycans tend to be negatively charged, because of the prevalence of acidic groups.

131

Mucopolysaccharides (Glycosaminoglycans)

Hyaluronate (hyaluronan) is a glycosaminoglycan with a repeating disaccharide consisting of 2 glucose derivatives, glucuronate (glucuronic acid) & N-acetyl-glucosamine.

The glycosidic linkages are b(1®3) & b(1®4).

132

Hyaluronate

H O

H

H

O HH

O H

COO

H

H O

O H H

H

NH COCH 3H

CH 2O H

H

OO

D -g lucuronate

O

1

23

4

5

61

23

4

5

6

N -acetyl-D -g lucosam ine

hyaluronate

Heparan sulfate is initially synthesized on a membrane-embedded core protein as a polymer of alternating N-acetylglucosamine and glucuronate residues.

Later, in segments of the polymer, glucuronate residues may be converted to the sulfated sugar iduronic acid, while N-acetylglucosamine residues may be deacetylated and/or sulfated.

133

Heparan Sulfate

H O

H

OSO3H

OH

H

COOO H

H

NHSO3H

OH

CH2OSO3

H

H

H

O

O

heparin or heparan sulfate - examples of residues

iduronate-2-sulfate N-sulfo-glucosamine-6-sulfate

Heparin, a soluble glycosaminoglycan found in granules of mast cells, has a structure similar to that of heparan sulfates, but is more highly sulfated.

When released into the blood, it inhibits clot formation by interacting with the protein antithrombin.

Heparin has an extended helical conformation.

134

Heparin

135

Some More GAG’s

Importance of carbohydrates

We use them as our major energy source (4 kcal/g) Humans : starch, sucrose and fructose 80% of our energy intake (average)

We use them for their sweet taste We use them to provide structure and texture in food

products Bread & pudding (starch); Dextrin (soft drinks); Pectin

(jellies) We use them to lower water activity of food products

and also influence ice crystallization Intermediate moist foods; Ice cream

Importance of carbohydrates

We use them as fat substitutes Modifies starches & celluloses, and gums

We use them to impart desirable flavors and colors for certain food products Maillard browning

We use them as an energy source in fermentation reactions Yogurt

We use them for their reported health “benefits” Dietary fiber

carbohydrates for ug

Documents

polymers monomers

simpler sugars

chemical energy

number of sugar units

individual monomers

etc10 monosaccharides

unique macromolecules

elements c