Carbohydrate Chemistry 2 PDF

carbohydrate chemistry (2) Disaccharides & Polysaccharides Biochemistry 1 Code (4125 ) Objectives By the end of the lecture, the student should know: ❑Definition of disaccharides ❑Classification of disaccharides ❑Classification and importance of polysaccharides DISACCHAR...

carbohydrate chemistry (2) Disaccharides & Polysaccharides Biochemistry 1 Code (4125 ) Objectives By the end of the lecture, the student should know: ❑Definition of disaccharides ❑Classification of disaccharides ❑Classification and importance of polysaccharides DISACCHARIDES A disaccharide consists of two monosaccharides joined with each other by glycosidic linkage. Classification of disaccharides Disaccharides are classified according to their reducing property into: Reducing disaccharides as : - Maltose - Isomaltose - Lactose Non reducing disaccharides as : - Sucrose Maltose (malt sugar) It is composed of 2 glucose units. It is hydrolyzed by the action of maltase enzyme into 2 molecules of glucose. Carbon 1 Carbon 4 Free reducing group Lactose (milk sugar) It is composed of one galactose and one glucose units It is hydrolyzed by the action of lactase enzyme into galactose and glucose. Carbon 1 Carbon 4 Free reducing group  Some people don’t produce enough lactase, the enzyme that hydrolyzes lactose, and so they can’t digest lactose. Many adults become lactose intolerant, and develop abdominal cramps, nausea, diarrhea, excess gases and bloating after eating or drinking dairy products. Lactase can be added to milk products (or taken as a supplement) to overcome this problem. Sucrose (table sugar) It is composed of one glucose and one fructose units. Both aldehyde group of glucose and ketone group of fructose (reducing groups) are involved in glycosidic the linkage so, sucrose is non reducing sugar. It is hydrolyzed by the action of sucrase enzyme into glucose and fructose. Carbon 1 Carbon 2  S uc ras e S uc ros e G luc os e + F ruc tos e L ac tas e L ac tos e G luc os e + G alac tos e Maltas e Maltos e G luc os e + G luc os e Hydrolysis of disaccharides in the small intestine POLYSACCHARIDES These are the condensation products of more than 10 molecules of monosaccharide units per molecule. They are classified into two main groups: 1-Homopolysaccharides 2-Heteropolysaccharides Homopolysaccharides They contain only one type of monosaccharide units, they are classified according to the name of the building units: 1- Glucans: formed from glucose units: Glycogen Starch Cellulose 2-Fructans: formed from fructose units: Inulin. Glycogen It is the storage form of glucose in liver and muscles of animals and humans. It forms 10% of the weight of liver and 2% of the weight of skeletal muscles.  This molecule is a homopolymer of glucose. Glucose residues are linked linearly by a 1, 4 linkage. It is also highly branched, with a 1, 6 branch linkages occurring every 8-10 residues. It is a very compact structure that results from the coiling of the polymer chains. Starch It is the storage form of glucose in plant cells. Starch occurs as granules, composed of branched and linear polymers of glucose. Each starch granule contains two forms, amylose and amylopectin Starch has lower degree of branching than glycogen (branch every 20-30 residues). Amylose Amylopectin Found in the inner part of starch granule Found in the outer part of starch granule Form about 20% of starch Form about 80% of starch Linear unbranched-chain polysaccharide Branched-chain polysaccharide Formed of several hundreds of glucose Formed of several thousands of units per molecule glucose units per molecule Glucose molecules connected by α-1 – 4 Glucose molecules connected by α 1- 4 glycosidic bonds and α- 1 – 6 glycosidic bonds More soluble in water Less soluble in water Hydrolyzed by amylase to maltose units Hydrolyzed by amylase to maltose and isomaltose units Cellulose It is a linear polysaccharide in which glucose residues are connected by b 1,4 glycosidic linkage. The human body cannot produce b amylase so that they are unable to digest cellulose. Cellulose passes as such in stool, it absorbs water during its passage along the intestine, so increases the bulk of stool thus stimulate the intestinal contraction and prevents constipation.  Comparison between glycogen, starch, cellulose Glycogen Starch Cellulose Units a Glucose a Glucose b Glucose Structure Branching chain Amylose : Non branching Non branching chain (α 1,4 and α 1,6) chain (α- 1, 4) (b 1,4) Amylopectin : Branching chain (α 1,4 and α 1, 6 ) Occurrence Humans and animals Plants Plants Function Storage form of Storage form of glucose in Structural glucose in humans plants and animals a Glucose and b Glucose Heteropolysaccharides They contain two or more different monosaccharide units, the most important member of this group is Glycosaminoglycans (GAGs) which contain amino sugars GAGs are classified into: - Sulfate free GAGs as : Hyaluronic acid - Sulfate containing GAGs as: -Chondroitin sulfate -Dermatan sulfate -Keratan sulfate -Heparin Hyaluronic acid It is present throughout the body specially in synovial fluid, vitreous humour of the eye. It acts as lubricant and shock absorbent. Hyaluronidase enzyme (spread factor) is present in some bacteria and hydrolyzes hyaluronic acid in connective tissue allowing the spread of bacteria. It is present also in the caps of the sperms to help fertilization of the ovum. Chondroitin sulphate It is the most abundant GAGs in the body and found in cartilage, ligaments, bones, skin, cornea, brain and blood vessel. In cartilage it binds collagen and hold fibers in strong network, helps to maintain the shape of skeletal system and has a role in compressibility of cartilage in weight bearing. Heparin It is present in high concentration in mast cells (A type of white blood cells found in connective tissues), that present in lung, liver and arterial wall. It is an anticoagulant. Thank You