University:
Glendale Community College
Course:
BIO160 | Introduction to Human Anatomy and Physiology
Academic year:

2022
Views:

393

Pages:

7
Author:

Abram Pham

Section 7.3: Polysaccharides §Polysaccharides (glycans) - large numbers of monosaccharides connected by glycosidic linkages §Can be linear or branched §Two classes: homoglycans and heteroglycans §Smaller glycans -2 to 10 monomers called oligosaccharides §Most often attached to polypeptides as glycoproteins §N-linked by N-glycosidic bond with asparagine R amide nitrogen §O-linked through serine or threonine R group hydroxyl Section 7.3: Polysaccharides §Homoglycans §Found in starch, glycogen, cellulose, and chitin (glucose monomer) §Starch and glycogen are energy storage molecules while chitin and cellulose are structural §Chitin is part of the cell wall of fungi and arthropod exoskeleton §Cellulose is the primary component of plant cell walls ü Most abundant organic substance on earth §No fixed molecular weight - size is a reflection of the metabolic state of the cell producing them Section 7.3: Polysaccharides §Starch - energy reservoir of plant cells; significant source of carbohydrate in the human diet §Amylose - long, unbranched chains of D-glucose with a(1,4) linkages §Contains thousands of glucose monomers - molecular weight from 150,000 to 600,000 Da §Amylopectin - branched polymer containing both a(1,6) and a(1,4) linkages §Branch points occur every 20 to 25 residues; a1,6 linkages Amylose Section 7.3: Polysaccharides §Glycogen - carbohydrate storage molecule in animals; greatest abundance in liver and muscle cells §Up to 8–10% of the wet weight of liver cells and 2–3% in muscle cells §Similar in structure to amylopectin, with more branch points §More compact and easily mobilized than other polysaccharides Section 7.3: Polysaccharides Figure 7.34 (a) Amylopectin and (b) Glycogen Section 7.3: Polysaccharides §Cellulose - D-glucopyranosides linked by b(1,4) glycosidic bonds §Most important structural polysaccharide of plants (most abundant organic substance on earth) §Pairs of unbranched cellulose molecules (12,000 glucose units each) are held together by hydrogen bonding to form sheetlike strips, or microfibrils §Each microfibril bundle is tough and inflexible with a tensile strength comparable to that of steel wire §Important for dietary fiber, wood, paper, and textiles Cellulose Microfibrils Section 7.3: Polysaccharides §Heteroglycans – high molecular weight; consisting of more than 1 type of monosaccharide; linkages to proteins §N-linked (N-glycans) are linked via a b-glycosidic bond §O-linked (O-glycans) have a disaccharide core of galactosyl-b-(1,3)-N-acetylgalactosamine linked via an a-glycosidic bond to the hydroxyl of serine or threonine residues §Glycosaminoglycans (GAGs) – linear polymers with repeating disaccharide units § Five classes: hyaluronic acid, chondroitin sulfate, dermatan sulfate, heparin & heparin sulfate, keratin