Biochemistry Carb. Lecture 6

Polysaccharide It is formed of large no. of monosaccharide, they are divided into: 1- Homopolysaccharide: on hydrolysis it give the same kind of monosaccharide. 2- Heteropolysaccharide: on hydrolysis it give different kinds of monosaccharide. The important Homopolysaccharide: 1) Starch: it is the major source of carbon in the human diet, it is a mixture of about 20% amylose and 80% amylopectine.

(1) Amylose Straight chain polysaccharide made up of entirely of D(+) glucose joined by α 1,4 glycosidic bond.

(2) Amylopectine: Amylopectine differ from amylose, it consist of highly branced chain of glucose unit at carbon 6. It is estimated that such branching occurs of one in every glucose molcule in the chain.

2) Glycogen: It is formed of glucose molecules joined together by α 1,4 & α 1,6 glycosidic bond like amylopectine. The major source of glycogen is the starch in the food that we eat. Starch hydrolyzed by enzyme to glucose, the amount of glucose form in this way more than the body need, the excess glucose is converted to glycogen & stored in the liver. Between meals and during fasting the glycogen is hydrolyzed to glucose as need by the body.

3) Cellelose: It make a large part in plant tissues, cellulose made up of glucose molecules joined together by β 1,4 glycosidic bond, it differ from starch in two important ways: glycosidic bond in cellulose is β rather than α. The molecules of glucose are all arranged in long straight chain. In human there is no enzyme in the intestine responsible for hydrolysis of β 1,4 glycosidic bond. Cellulose therefore represent an indigestible part of the human.

4) Inuline: It is polysaccharide formed of fructose units joined together by β 1,2 glycosidic bond, it is hydrolyzed by acid and also by enzyme inulinaze to fructose. It give no color with iodine, it is not used as a source of food and it has no normal range in the blood. When inuline given intravenously, it is filtered by kidney, it is used to diagnose the renal function and diseases of the kidney by well known test called (Inuline Clearance Test).

Polysaccharides Many monosaccharides linked together The important ones to remember are: o Cellulose- 1,4’ beta links made by plants used as support substances- strong due to hydrogen bonding indigestible by humans because of the nature of the beta links o Starch- 1,4’ alpha links made by plants as energy storage digestible by humans because they are alpha links composed of two different polymers amylase- 1,4’ alpha links amylopectin- 1,4’ alpha and 1,6’ alpha (this is what causes the branching) Glycogen a lot like amylopectin, however there are less 1,6’ alpha links, so there is less branching.

Hetropolysaccharide (Mucopolysaccharide): It is a straight compound containing amino sugar and uronic acid, sometimes they are present as ester of sulfuric acid, they present in free or in combination with protein called glycoprotein or mucoprotein, they called acid mucopolysaccharide because they have acid group. Ex.: H 2 So 4 or CooH It is divided into:

C- Heparin: It is formed of (glucoseamine glucouronic acid with H 2 So 4 ). It is present in mast cells of the liver, lungs, spleen and connective tissues. Function of heparin: 1- It is anticoagulant of blood. 2- Produce lipoprotein lipase, it decrease the amount of fat in blood and changing the blood from turbid to very clear (it is a clearing factor).

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