Paper : 04 Metabolism of carbohydrates

Module : 01 Prelude: Carbohydrates (Part-B) -Polysaccharides

Principal Investigator Dr.S.K.Khare,Professor IIT Delhi.

Paper Coordinator Dr. Ramesh Kothari,Professor UGC-CAS Department of Biosciences

Saurashtra University, Rajkot-5, Gujarat-INDIA

Dr. S. P. SinghProfessor Content Reviewer UGC-CAS Department of Biosciences Saurashtra University, Rajkot-5, Gujarat-INDIA

Dr.Charmy Kothari, Assistant Professor Department of Biotechnology Content Writer Christ College, Affiliated to Saurashtra University, Rajkot-5, Gujarat-INDIA

1

Metabolism of Carbohydrates Biochemistry Prelude: Carbohydrates (Part-B)-Polysaccharides

Description of Module

Subject Name Biochemistry

Paper Name 04 Metabolism of Carbohydrates

Module Name/Title 01 Prelude: Carbohydrates (Part-B)-Polysaccharides

Dr. Vijaya Khader Dr. MC Varadaraj

2

Metabolism of Carbohydrates Biochemistry Prelude: Carbohydrates (Part-B)-Polysaccharides

PRELUDE-CARBOHYDRATES- Polysaccharides Objectives

1. Introduction and properties of polysaccharides

2. To know about homopolysaccharides and its properties

3. To know about heteropolysaccharides and its properties

3

Metabolism of Carbohydrates Biochemistry Prelude: Carbohydrates (Part-B)-Polysaccharides

Introduction

 Our body requires diverse types of food to carry out a variety of functions, maintenance and growth

 We can classify food largely into carbohydrates, proteins and fats. Fats help in long term storage of energy and cannot be utilized right away. Proteins facilitate building muscles and tissues

 The carbohydrates, as they can be broken down immediately into glucose provide us the energy required to do immediate work

 A molecule of carbohydrate consisting a number of molecules of sugars linked together by glycosidic linkages is called a polysaccharide. For instance, storage polysaccharides such as Starch and Glycogen and structural polysachharides such as Cellulose and chitin ).

 These polysaccharides give the constituent monosaccharises or oligosachharides when they hydrolyzed.  They are either linear or extremely branched structure and are  Polysaccharides are heterogeneous due to minor modifications of the repeating unit and based on the structure, these macromolecules have different properties compared to their monomeric building blocks  Polysaccharides can be amorphous and even insoluble in water  Polysaccharides are of two kinds, (i) homopolysaccharide or (ii) heteropolysaccharides based on types of monosachharides.  Polysaccharides consisting the same type of monosaccharides is called homopolysaccharide and polysaccharides consisting more than one type of monosaccharides are called heteropolysaccharides .

4

Metabolism of Carbohydrates Biochemistry Prelude: Carbohydrates (Part-B)-Polysaccharides

How are Polysaccharides processed in our Body?

 The food we eat is mixed with enzymes released by the body at various points to assist in the digestion of the diverse molecules like carbohydrates, fats as well as proteins  Chewing helps in break apart the carbohydrates into smaller pieces. It is in the stomach followed by the small intestine that the ultimate breakdown of the polysaccharides occurs  The acid released in the stomach breaks these polysaccharides into monosaccharides. These monosaccharides are glucose molecules and are basic source of energy  The glucose is further broken down in the cells into molecules of Adenosine Triphosphate in order to be utilized by the body to perform work as and when needed.

Properties of polysaccharides

 Carbohydrates composed of ten or more monosaccharides units are generally classified as polysaccharides and their molecules are colloidal in size.  Polysaccharides may be considered as condensation polymers in which the monosaccharides are joined together by glycosidic linkages.  Polysaccharides are also termed as glycans  Polysaccharides when composed of a single monosaccharide building block are called homopolysaccharides (homoglycans). Polysaccharides when composed of more than one type of monosaccharide are called heteropolysaccharides (heteroglycans).  Glucose polysaccharides are “glucans”, fructose polysaccharides are fructans and polysaccharides made of mannose and xylose are called mannans and xylansrespectively

 Some polysaccharides contains units that are derivatives of the monosaccharides for example. Chitin

5

Metabolism of Carbohydrates Biochemistry Prelude: Carbohydrates (Part-B)-Polysaccharides

 Chitin is made up of the amino sugar, glucosamine and hyaluronic acid is composed of glucuronic acid and glucosamine

 Monosaccharides units of polysaccharides are joined by glycosidic linkage, the polysaccharides are readily hydrolyzed by mineral acids but are resistant to alkaline hydrolysis

Homopolysaccharides Starch

 Starch is presentas insoluble granules in the cytoplasm.  Starch is a mixture of two polymers amylose and amylopectin  Amylose is a linear polysaccharide and amylopectin is a highly branched polysaccharide  Amylose - The constituent of starch in which glucose units are linked by -D-1 4 glycosidic bonds to form linear chains  The level of amylose and its molecular weight vary between different types of starch  Amylose molecules are normally made from 200-2000 glucose units. Aqueous solutions of amylose are very unstable because of intermolecular attraction and association of neighboring amylose molecules  Amylose forms a helical complex when tested with iodine giving a characteristic blue color  Amylopectin- Amylopectin is the branched form, most of the constituent of glucose residues are joined by -D-1 4 glycosidic bonds and additional -D-1 6 glycosidic bonds every 25-30 residues forms the branched structure

6

Metabolism of Carbohydrates Biochemistry Prelude: Carbohydrates (Part-B)-Polysaccharides

Structure of Starch

Glycogen  Glycogen like starch yields glucose upon acid hydrolysis hence is a polymer of glucose.  Glycogen occurring wide spread in animal tissues, especially liver and muscle which give a red-brown, red, or at a times violet color with iodine  Glycogen is highly branched structure. The chain glycosidic linkage is -1 4, the branching occurs with a glycosidic linkage of -1 6.  β-amylase acts upon glycogen to give considerable amounts of maltose indicating the presence of -1 4glycosidic linkage

7

Metabolism of Carbohydrates Biochemistry Prelude: Carbohydrates (Part-B)-Polysaccharides

Structure of Glycogen Cellulose

 Cellulose is another polymer of the monosaccharide glucose.  Cellobiose is the disaccharide obtained by the hydrolysis of cellulose indicates that the linkage of glucose units in cellulose are as they are in cellulose  It is resistant to hydrolysis and requires the action of strong acids  Cellulases capable of hydrolyzing cellulose are absent from animal digestive juices and hence itcannot be digested by human beings.  Cellulose, also known as plant fiber, plant cell wall is made of cellulose.  It is also insoluble in water.

8

Metabolism of Carbohydrates Biochemistry Prelude: Carbohydrates (Part-B)-Polysaccharides

 The glucose units in cellulose form a two-dimensional structure with hydrogen bonds holding together nearby polymers thus giving the molecule more stability which makes cellulose differs from starch and glycogen because  Cellulose is not soluble in water.  Cellulose does not give a characteristic reaction with iodine  Cellulose cannot be used as an energy source because of its complexity but cellulose fiber is essential in the nutritionas it helps the digestive track exercising and keep it healthy and clean.

Structure of Cellulose

Inulin  Inulin is a polysaccharide composed of D-fructose  It occurs as the reserve carbohydrates in the tubers  Inulin is a white, more or less crystalline powder  It is readily soluble inhot but slightly soluble in cold water  Inulin when heated with water it does not gelatinize like starch  It is not utilized as a food and is used as a source of commercial fructose

9

Metabolism of Carbohydrates Biochemistry Prelude: Carbohydrates (Part-B)-Polysaccharides

Structure of Inulin Chitin  Chitin is a condensation product of acetyl glucosamine  It is the structural material of the arthropoda  It forms the exoskeleton of the crustaceans, insects etc.  The chitin molecules are the chains of acetyl glucosamine units linked similarly as the glucose units in cellulose  Chitin is highly resistant to the action of solvents and of bacteria

Structure of Chitin

10

Metabolism of Carbohydrates Biochemistry Prelude: Carbohydrates (Part-B)-Polysaccharides

Heteropolysaccharides

Agar  Agar is a vegetable mucilage obtained from seaweeds  It is a sulfuric acid ester of a complex galactose polysaccharide  Agar is odorless and tasteless  It swells strongly in cold water but does not dissolve  It dissolves in hot water to form a sol which upon cooling sets as a gel  It is a very valuable as a supporting agent in bacterial culture media

Gum Arabic  Vegetable gums are carbohydrates materials containing hexoses or pentose’s or both in glycoside union and a carbohydrate acid group  Hydrolysis of gums usually yield galactose and arabinose or xylose alone or in mixtures  Gum Arabic is one of the important and best known gums  It is used in the preparation of pharmaceuticals, in confections and as an adhes ive

Pectin  Pectin is found especially in the pulp of citrus fruit, apples, beets and carrots  Pectin is the term used to represent the substance or substances which in the presence of sugar and the proper acid concentration causes the formation of jellies  Commercial pectin is generally prepared from cull lemons or apple pomace  Pectin is combined with cellulose in the cell walls from which it may be released by mild hydrolysis or other means and converted to soluble pectin  Insoluble pectin is referred to as protopectin 11

Metabolism of Carbohydrates Biochemistry Prelude: Carbohydrates (Part-B)-Polysaccharides

Structure of Pectin

Hyaluronic acid  Hyaluronic acid serve as an integral part of the gel like ground substance of connective and other tissues and as a lubricant and shock absorbent in joints  It appears to be an unbranched or nearly unbranched chain polymer of N-acetylated hyaluronic acid units  Hyaluronic acid upon hydrolysis yield equimolecular quantities of D-glucosamine, D- glucuronic acid and acetic acid  In tissue it acts as a cementing substance and contributes to tissue barriers which permit metabolites to pass through but resist penetration by bacteria and other infective agents

Heparin  Heparin is blood anticoagulant  It is present in liver, lung thymus spleen and blood  It is polymer of D-glucuronic acid and D-glucosamine  In this amino groups and some of the hydroxyl groups are combined with sulfuric acid

12

Metabolism of Carbohydrates Biochemistry Prelude: Carbohydrates (Part-B)-Polysaccharides

Structure of Heparin

Chondroitin sulfates  The chondroitin sulfates are among the principal mucopolysaccharides in the ground substance of mammalian tissues and cartilage, and occur combined with proteins  Three chondroitin sulfates are isolated and designated chondroitin A, B and C  Chondroitin sulfate A is present in the cartilage, adult bone and cornea  Chondroitin sulfate B is present in the skin, heart valves and tendon  Chondroitin sulfate C is present in the cartilage and tendon  Chondroitin sulfate A and C appears to be made of equimolar quantities of N-acetyl- 2amino-2-deoxy-D-galactose, D-glucuronic acid and sulfuric acid  Chondroitin sulfate B also known as heparin and more frequently designated dermatan sulfate (from skin) is the sulfate of a polysaccharide composed ofL- iduronic acid and N-acetylgalactosamine

13

Metabolism of Carbohydrates Biochemistry Prelude: Carbohydrates (Part-B)-Polysaccharides