carbohydrates chemistry, lecture for 1st year m b b s . delivered by dr mohammad waseem kausar

Dr MUHAMMAD WASEEM KAUSARAssistant professor. Bio-chemistry

I M D C.

Carbohydrates chemistry

Carbohydrates

– Cell structure:– Cellulose, LPS, chitin

Cellulose in plant cell walls Lipopolysaccharides (LPS) in bacterial cell wall

Chitin in exoskeleton

The elements which make up carbohydrates are:

•Carbon (C)•Hydrogen (H)•Oxygen (O)Some carbohydrates also contain N and S

Carbohydrates• commonly known as sugars, Saccharide, hydrates

(H2o) of carbon• ARE ALDEHYDE OR KETONE DERIVATIVES OF

POLYHYDRIC ALCOHOLS or• Are polyhydroxylated compounds with at least 3 carbons, with

potentially active carbonyl group, which may be either aldehyde(CHO) or ketone (CO) group.

• general formula CnH2nOn .but

Many CHO contain H & O not in the same proportionAs in water .e.g deoxyriboseC5H10O4.

• Sources– Plants– animals

BIOMEDICAL IMPORTANCE • A variety of functions in the cell

– Provides majority of energy(4.1 kilocalories/gm)– Structural component of cell wall.– In animal cells carbohydrates on the exterior surface of the cell

serve a recognition and identification function– Serve as metabolic intermediate(G-6-p)– Component of nucleotides that form DNA , RNA – precursor for synthesis of all the other carbohydrates in the body

e.g. glycogen, galactose, ribose, glycolipids, glycoproteins and proteoglycans.

– For synthesis of FA, cholesterol, amino acids– Carbohydrates derivatives are used as drugs e.g.– Principal sugar in milk, galactose– Strong detoxification agent in body e.g. Glucoronic acid– Play a role in lubrication, cellular intercommunication, and

immunity.– Diseases ssociated with carbohydrate metabolism include Diabetes

mellitus, galactosemia, glycogen storage diseases, and lactose intolerance.

Carbohydrates Classificationno satisfactory classification. •GENERALLY 1.Simple carbohydrates2.Complex carbohydrates

• On the basis of hydrolysis1.Monosaccharides2.Disaccharides3.Oligosaccharides, 4.Polysaccharides. and .Derived carbohydrates

MonosaccharidesMonosaccharides

Monosaccharides -Single Sugar-

•Glucose

The Formula for glucose is

C6 H12 O6

9

Glucose

C

C

CH2OH

H OHC

OHH C

HHO

H OH

C OH

D-Glucose

10

Fructose

C

C

CH2OH

H OHC

OHH C

HHO

O

CH2OH

D-Fructose

• These are the basic building blocks of other carbohydrates

• Simple sugars• Can not be further hydrolyzed• Name usually suffix - ose• Empirical formula is CnH2nOn, here “ n” =3 or more• Color less, white, solid crystalline in nature, soluble

in water, sweet taste, insoluble in non-polor solvent• Simplest m/s are two, which are 3 carbon. Trioses

glyceraldehyde & dihydroxyacetone.• Subdivision of m/s1.On the basis of “C” atoms.2.On the basis of functional group.

Classification of m/s

1.number of carbons

14

2.On the basis of functional group

• Aldoses are monosacchrides with an aldehyde group and many hydroxyl (-OH) groups.

• Ketoses are monosacchrides with a ketone group and many hydroxyl (-OH) groups.

Some properties of m/s with reference to glucose

chiral Carbon:

ISOMERS=

2n.

1. Monosaccharides contain one or more asymmetric C-atoms: get D- and L-forms, where D- and L- designate absolute configuration

2. D-form: -OH group is attached to the right of the asymmetric carbon

3. L-form: -OH group is attached to the left of the asymmetric carbon

4. If there is more than one chiral C-atom: absolute configuration of chiral C furthest away from carbonyl group determines whether D- or L-

Chirality rules.

Ring formation / Ring structure

An aldose: Glucose

A ketose: Fructose

Ring Structure

• Linear known as “Fischer” structure”• Ring know as a “Haworth projection”• Cyclization via intramolecular hemiacetal (hemiketal)

formation• C-1 becomes chiral upon cyclization - anomeric

carbon• Anomeric C contains -OH group which may be or mutarotation

EPIMERS•Carbohydrate isomers that differ in configuration around only one specific carbon atom (with the exception of the carbonyl carbon) Epimers: Isomers differing as a result of variations in configuration of the -OH and -H on carbonatoms 2, 3, and 4 of glucose are known as epimers. . For example, glucose and galactose are C-4 epimers ,their structures differ only in the position of the -OH group at carbon 4

OPTICAL ACTIVITY

• The presence of asymmetric carbon atoms also confers optical activity on the compound. When a beam of plane-polarized light is passed through a solution of an optical isomer, it will be rotated either to the right, dextrorotatory (+); or to the left, levorotatory (−). The direction of rotation is independent of the stereochemistry of the sugar, so it may be designated D(−), D(+), L(−), or L(+). For example, the naturally occurring formof fructose is the D(−) isomer.