1. CARBOHYDRATE CHEMISTRY
DR SHAMIM SHAIKH MOHIUDDIN DEPT OF BIOCHEMISTRY UNIVERSITY OF DAMMAM KSA

2. OVERVIEW
-Carbohydrate primarily composed of Carbon, Hydrogen
and Oxygen
-Carbohydrates may be defined as polyhydroxyaldehyde or polyhydroxyketones or compounds which produce them on hydrolysis
CLASSIFICATION OF CARBOHYDRATE
-Mainly classified into three major groups depends on number of sugar units
-Monosaccharides
-Oligosaccharides
-Polysaccharides

3. Monosaccharides
-Monosaccharides are the simplest group of carbohydrate
and cannot be further hydrolyzed.
-Monosaccharides are divided into different categories,
based on the functional group and number of C atoms.
Aldose:
When functional group in monosaccharides is an
aldehyde group(-CHO) they are known as Aldose
example- glucose
Ketose:
When functional group in monosaccharide is an
ketone group(-CO) they are known as Ketose
example-fructose

4. Oligosaccharides
-Oligosaccharides contain 2-10 monosaccharide molecule
which are liberated on hydrolysis
-Based on the number of monosaccharide units they are
Further classified into disaccharides, trisaccharides etc
Polysaccharides
-Polysaccharides are polymers of monosaccharides unit
With high molecular weight
-Polysaccharides are of two types
-Homopolysaccharides
-Heteropolysaccharides

5. STRUCTURAL ASPECT OF MONOSACCHARIDE
=Stereoisomer=
Stereo isomers refers to a compound that have the same structural formula but differs in their spatial configuration.
-Stereoisomerism is a very important character of monosaccharides
=Asymmetric carbon atom=
A carbon atom is said to be asymmetric when it is attached to four different atoms or group.

6. D and L isomers
-D and L isomers are mirror images of each other
-The spatial orientation of –H and –OH groups on the
carbon atom that is adjacent to the primary alcohol carbons determines whether. the sugar is D- or L- form.
-OH in right side : D-series sugar
-OH in left side : L-series sugar

7. Optical activity of sugars
-Optical activity is a characteristic feature of compounds
with asymmetric carbon
-A beam of polarized light when passed through a solution of an optical isomer, it will be rotated either to the right or left.
Rotation of polarized light to right- Dextrorotatory(+)
Rotation of polarized light to left- Levorotatory(-)
Racemic mixture
-If D and L isomers are present in equal concentration
is known as Racemic mixture
-Racemic mixture does not show any optical activity since the dextro and levorotatory activities cancel each other

8. Epimers
-If two monosaccarides differ from each other in their configuration around a single specific carbon(other than anomeric) atom, they are referred to as epimers to each other.
-Example: Glucose and Galactose are epimers with regards to carbon no 4

9. Enantiomers
Enantiomers are a special type of stereoisomerism that are mirror images of each other.
-The two members are designated as D and L sugars
-Majority of the sugars in the higher animals(including man) are of D type
Diastereomers
-This represents the stereo isomers that are not mirror image of one another.

10. Anomer
-The α and β cyclic forms of D-glucose are known as anomer.
-They differ from each other in configuration only around
C1 which is known as anomeric carbon atom
-In α anomer, the –OH group held by anomeric carbon is on the opposite side of the group –CH2OH of sugar ring
-In β anomer, the –OH group held by anomeric carbon is on the same side of the group –CH2OH of sugar ring

11. Mutarotation
-Mutarotation is defined as the change in the specific optical rotation representing the interconversion of α and β forms of D glucose to an equilibrium mixture
α –D-glucose ↔ Equilibrium mixture ↔ β-D-glucose
º º º
-The Equilibrium mixture contains
β anomer – 63℅
α anomer – 36℅
open chain form - 1℅
-β form is more predominant due to its stable conformation

12. DISACCHARIDES
Disaccharides consists of two monosaccharides units held together by a glycosidic bond.
-They are crystalline, water soluble and sweet to taste.
-Disaccharides are of two types
-Reducing disaccharides with free aldehyde or keto gr
e.g. Maltose, Lactose
-Non reducing disaccharides with no free aldehyde or keto gr. e.g. Sucrose
Maltose
-Composed of two α-D-glucose units held together by
Glycosidic bond.
-Maltose can be hydrolyzed by dilute acid or enzyme maltase to liberate two molecules of α-D-glucose

13. Lactose
-Lactose is more commonly known as milk sugar.
-It is composed of β-D-galactose and β-D-glucose held together by glycosidic bond.
-It is hydrolyzed by intestinal enzyme Lactase to glucose and galactose.

14. Sucrose
-Sucrose is made up of α-D-glucose and β-D-fructose
-Two monosaccharides are held together by a glycosidic bond, between C1 of α-glucose and C2 of β-fructose.
-Sucrose is a non-reducing sugar because the reducing group of glucose and fructose are involved in glycosidic bond.
-Sucrose is most abundant among the naturally occurring sugars and important sources of dietary carbohydrate
-It is sweeter than most other common sugar except fructose.
-the intestinal enzyme, sucrase, hydrolyzed sucrose to glucose and fructose.

15. POLYSACCHARIDES
-It consist of repeat units of monosaccharides or their derivatives, held together by glycosidic bonds.
-Polysaccharides are linear as well as branched polymer
-Two types
1. Homopolysaccharides
-Homopolysaccharides on hydrolysis yield only a single type of monosaccharides.
-They are named based on the nature of the monosaccharide units. e.g.
-Glucans are polymers of glucose
-Fructosans are polymers of fructose
2. Heteropolysaccharides
-Heteropolysaccharides on hydrolysis yield a mixtureof few monosaccharides or their derivatives

16. n Starch -Also known as glucosan or glucan
-It is a homopolysaccharide composed by D-glucose units
which is held by α(1→4)-glycosidic bonds
-Starch consists of two polysaccharide components
a. Water soluble amylose(15-20%)
b. Water insoluble amylopectin(80-85%)
-Chemically amylose is a long unbranched chain with D-glucose units held by α-(1→4) glycosidic linkage H H H H 5 5 4 1 4 1 O O 3 2
α(1→4)Glycosidic bond 3 2 n
D-Glucose
D-Glucose

17. -Amylopectin containing few thousand glucose units looks like a branched tree(20-30 glucose units per branch).It is a branched chain with α(1→6) glycosidic bonds at the branching points and α(1→4) glycosidic bond everywhere
Else. H 5 H 5 4 1 4 1 O 6 3 2 O 3 2
α(1→6)glycosidic bond
CH2OH 6
CH2 H 5 5 H H H H 1 4 4 1 O O 3 2 3 2
α(1→4)glycosidic bond

18. Glycogen
-Glycogen is the carbohydrate reserve in animals.
-Present in Liver, muscle and brain
-Structure of glycogen is similar to that of amylopectin with more number of branches.
-Glucose is the repeating unit in glycogen joined together by α(1→4)glycosidic bond andα(1→6)glycosidic bonds at branching points.

19. Cellulose
-Cellulose occurs exclusively in plants and totally absent in animal body.
-It is composed of β-D-glucose units linked by β(1→4)glycosidic bonds
-Cellulose cannot be digested in human, due to lack of the enzyme that cleaves β-glycosidic bond 5 5 H H 1 4 4 1 O 3 2 3 2
β(1→4)glycosidic bond
β-D-Glucose
β-D-Glucose n