Chapter 14 14.6 – Polysaccharides

Polysaccharides A polymer of many monosaccharides joined together Four biologically important polysaccharides: Amylose Amylopectin Glycogen Cellulose All are polymers of D-glucose that differ only in the type of glycosidic bonds and the amount of branching in the molecule

Starch Starch is a storage form of glucose in plants Found as insoluble granules is rice, wheat, potatoes, beans and cereals Starch is composed of two kinds of polysaccharides – amylose and amylopectin

Amylose Amylose – makes up about 20% of starch Contains 250 to 4000 α-D-glucose molecules connected by α-1,4-glycosidic bonds in a continuous chain They are actually coiled in a helical fashion

Amylopectin Amylopectin – makes up about 80% of starch Glucose molecules are connected by α-1,4-glycosidic bonds in a branched chain About every 25 glucose units there is an α-1,6-glycosidic bond

Glycogen Animal starch that is a polymer of glucose that is stored in the liver & muscle of animals Hydrolyzed in our cells at a rate that provides energy between meals Structure is similar to amylopectin but it is more highly branched Glucose units are joined by α-1,4-glycosidic bonds with branches occurring about every 10-15 glucose units attached by α-1,6-glycosidic bonds

Cellulose Is a polysaccharide of glucose units in unbranched chains Has β-1,4-glycosidic bonds – do not form coils like the α isomers but are aligned in parallel rows (insoluble in water) Cannot be digested by humans - we cannot break down β-1,4-glycosidic bonds

Cellulose Cotton is almost pure cellulose

Carbohydrates in Our Diet