CARBOHYDRATES Most abundant organic molecule in nature. Literally means ‘hydrates of carbon’ i.e.

(C.H2O)n. When n is 3 it satisfies the definition of

hydrates of carbon. Several non-carbohydrates also satisfies the

definition of hydrates of carbon i.e. acetic acid(C2H4O3), lactic acid (C3H6O3).

Some of the genuine carbohydrates where n is above 3 do not satisfy the general formula.

Hence Carbohydrates cannot be always considered as hydrates of carbon.

DEFINITION

Carbohydrates may be defined as polyhydroxy-aldehydes or Ketones or compounds which produce them on hydrolysis.

The term ‘sugar’ is applied for carbohydrates soluble in water and sweet in taste.

FUNCTIONS

The most abundant dietary source of energy (4cal/g) for all organism.

Precursors for many organic compounds (fats, amino acids etc).

Carbohydrates ( as glycoprotein and glycolipids) participate in the structure of cell membranes and cellular functions such as cell growth etc.

FUNCTIONS

Structural components of many organisms like the fiber (cellulose) of plants, exoskeleton of some insects and the cell wall of microorganisms.

Also serve as the storage form of energy(glycogen) to meet the immediate energy demands of the body.

They are utilized as raw materials for several industries e.g. paper, plastic, textile alcohol etc.

CLASSIFICATION

Carbohydrates are often referred to as saccharides .

Broadly classified into 3 groups.

1. Monosaccharides2. Oligosaccharides3. polysaccharides

MONOSACCHARIDES

Simplest form of carbohydrates and are referred as simple sugars.

Have general formula Cn(H2O)n. They cannot be further hydrolyzed. Further classified based on the

functional groups and the number of carbon atoms.

Based on the functional groups they are classified as

1. Aldoses: Aldehyde as functional group2. Ketoses: ketone as functional group

MONOSACCHARIDES Based on the number of carbon atoms they

are classified as

1. Trioses: 3 carbon2. Tetroses: 4 carbon3. Pentoses: 5 carbon4. Hexoses: 6 carbon5. Heptoses: 7 carbon

These terms are used along with functional groups while naming monosaccharides.

e.g. Glucose is Aldohexose and Fructose is Ketohexose.

MONOSACCHARIDES

MONOSACCHARIDES

MONOSACCHARIDES

OLIGOSACCHARIDES Contains 2-10 monosaccharide molecules

which are liberated on hydrolysis. Based on the number of

monosaccharides units present they are subdivided as.

1. Disaccharides : On hydrolysis produce 2 molecules of

the same or different monosaccharide.I. Maltose Glucose + Glucose II. Sucrose Glucose + FructoseIII. Lactose Glucose + Galactose

OLIGOSACCHARIDES

2. Trisaccharides : Contains 3 monosaccharide units . Raffinose Fructose+Galactose+Glucose

3. Tetrasaccharides : Contains 4 monosaccharide units.Stachyose 2(Galactose)+Glucose+Fructose

4. Pentasaccharides : Contains 5 monosaccharide units.Verbascose 3(Galactose)+Glucoce+Fructose

POLYSACCHARIDES They are polymers of monosaccharides units

with high molecular weights(up to million). They are usually tasteless(non-sugars) and

form colloids with water. They are of 2 types. 1. Homopolysaccharides (Homoglycans): Contain monosaccharide units of a single

type. E.g. Starch,Glycogen,Inulin,Cellulose.2. Heteropolysaccharides (Heteroglycans): Possess 2 or more different types of

monosaccharides units or their derivatives. E.g. heparin, chondroitin sulfate.

IMPORTANT CONCEPTS

1) Asymmetric Carbon: When it is attached to 4 different atoms

or groups. The number of asymmetric carbons(n)

determines the possible isomers of a given compound which is equal to 2n .

Glucose contains 4 asymmetric carbons and thus has 16 isomers.

IMPORTANT CONCEPTS

2) Stereoisomers: Stereoisomers are the compounds that

have same structural formulae but differ in their spatial arrangement.

Stereoisomerism is an important character of monosaccharides.

Glyceraldehyde has one asymmetric carbon atom and hence exists as 2 Stereoisomers.

Glyceraldehyde has been chosen as reference carbohydrate to represent the structure of all other carbohydrate.

IMPORTANT CONCEPTS

IMPORTANT CONCEPTS

3) D and L isomers: D and L isomers are mirror images of

each other. The spatial arrangement of –H and –OH

groups on the carbon atom that is adjacent to the terminal primary alcohol carbon determines whether the sugar is D or L type.

If the –OH group is on the right side the sugar is of D series and if on the left side it belongs to L series.

IMPORTANT CONCEPTS

The naturally occurring monosaccharide in mammalian tissues is mostly of D series.The enzyme machinery of cells is specific to metabolize D series of monosaccharide.

IMPORTANT CONCEPTS4) Optical activity of sugars: Optical activity is characteristic of

compounds with Asymmetric carbon atom.

When a beam of polarised light is passed through a solution of an optical isomer it will rotate either to the right or left.

When it rotates to right it is called Dextrorotatory and when it rotates to left it is called Levorotatory.

IMPORTANT CONCEPTS

5) Racemic mixture: When D and L isomers are present in

equal concentration it is known as Racemic mixture or DL mixture.

Racemic mixture does not exhibit any optical activity since the Dextro and Levorotatory activities cancel each other .

Optical activity of Racemix mixture is Zero.

IMPORTANT CONCEPTS6) Epimers: If 2 monosaccharides differ from each

other in their configuration around a single specific carbon (other than Anomeric carbon) they are referred as Epimers of each others.

Glucose and Galactose are Epimers with regards to carbon 4 (C4 Epimers).

Glucose and mannose are Epimers with regards to Carbon 2 ( C2 Epimers).

IMPORTANT CONCEPTS

•The interconversion of Epimers(glucose to Galactose and vice versa) is known as Epimerization.•The enzyme which catalyze this reactions are called as Epimerases.