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Medical Biochemistry and Molecular

Biology

CARBOHYDRATE CHEMISTRY

ByDr.Hussein Abdelaziz

Definition:

Carbohydrates are polyhydroxy aldehydes or

polyhydroxy ketones and compound giving them

on hydrolysis

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Carbohydrates are :

Organic compounds composed of C.H.O.

Generally but not always the hydrogen and oxygen

in carbohydrates are present in the proportion of

2H and one oxygen atoms as in water.

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Classification Monosaccharides Disaccharides Oligosaccharides Polyosaccharides

Diff The simplest

carbohydrates.

They contain only

one sugar unit .

-cannot be

hydrolysed into

simpler units

2 monsacch.

Units linked to

each other by

glycosidic bond

3-10 monsacch. Units linked to

each other by glycosidic bond

More than 10

monsacch. Units

linked to each other

by glycosidic bond

Ex. Glucose …. Sucrose &

Lactose……

1-Maltotriose = 3 glucose units

2-Raffinose

(tri-saccharide=

glucose+glactose+fructose)

Starch …….

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Monosaccharides

Are carbohydrates which, contain only one sugar

unit and cannot be hydrolyzed into smaller units

( the simplest form of carbohydrates).

They are further classified according to:

1. Whether they are aldehydes or ketones.

2. Number of carbon atoms contain.

3. According to number of carbon atom as well as

aldehydes and ketones.

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Number of Carbons

(Generic

monosaccharide

name)

Aldose Functional

Group

Ketone Functional

Group

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(Triose)Aldotriose Ketotriose

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(Tetrose)Aldotetrose Ketotetrose

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(Pentose)Aldopentose Ketopentose

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(Hexose)Aldohexose Ketohexose

Aldoses

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Ketoses

Asymmetric carbon atom (chiral carbon)

Def: It is a carbon atom which is attached to 4

different group or atoms e.g. middle carbon of

glyceraldhyde.

Any substance having asymmetric carbon atom

posses the following:

I. Show optical activity.

II. Show optical isomerism (stereoisomerism)

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Optical activity

DIFF: It is the ability of the compound to rotate

plane polarized light either towards the right or

towards the left.

Plane polarized light: is an ordinary light its

waves pass in one direction by the action of special

prism called Nicols prism (CaCO3),

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Types of optically active sugar solutions

A. If the compound rotate plane polarized light to the right, it

is called >>>>dextrorotatory, d or (+).

Example: Glucose is dextrorotatory so it is sometimes called

dextrose.

B. If the compound rotate plane polarized light to the left, it

is called>>>>>. levorotatory, l or (-).

Example: Fructose is levorotatory so it is sometimes called

levulose.

NB :All monosaccharides are optically active, except

dihydroxy acetone, this is due to the presence of

asymmetric carbon atoms.14

10/14/2014 15Ahmed A.Albadry

GREAT

THANKSHussein Abdelaziz