CHAPTER 5 THE STRUCTURE AND FUNCTION OF MACROMOLECULES Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings Section B: Carbohydrates - Fuel and Building Material 1.Sugars, the smallest carbohydrates, serve as fuel and carbon sources 2.Polysaccharides, the polymers of sugars, have storage and structural roles

include both sugars and polymers simplest carbs are monosaccharides or simple sugars disaccharides consist of 2 monosaccs polysaccharides are polymers of monosaccs Carbs (general) Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

monosaccs generally have molecular formulas that are some multiple of CH 2 O EX. glucose = formula C 6 H 12 O 6 most names for sugars end in -ose they have a carbonyl group and multiple OH groups carbonyl group is at the end = an aldose (glucose) if carbonyl is not = a ketose (fructose) What are structural isomers? Monosaccharides Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

are also classified by the # of carbons in the backbone (hexose, pentose, triose, etc.) may also exist as enantiomers EX glucose and galactose Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

Fig. 5.3

monos (particularly glucose) are a major fuel for cellular work also function as raw material for synthesis of other monomers (like amino acids and fatty acids) Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings Fig. 5.4

2 monos can join w/ a glycosidic linkage to form a dissaccharide via dehydration maltose = two glucose molecules sucrose = (table sugar) glucose and fructose Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings Fig. 5.5a

Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings Fig. 5.5 while often drawn as a linear skeleton, in aqueous solutions monos form rings

are polymers of 100s to 1000s of monosaccharides joined by glycosidic linkages function as an energy storage macromolecule that is hydrolyzed as needed can also serve as building materials for the cell or whole organism Polysaccharides Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

starch is a storage poly composed entirely of glucose monomers most monomers are joined by 1-4 linkages between glucose molecules 1 unbranched form of starch, amylose, forms a helix branched forms, like amylopectin, are more complex Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings Fig. 5.6a

plants store starch within plastids, including chloroplasts plants can store surplus glucose in starch and withdraw it when needed for energy or carbon animals that feed on plants, especially parts rich in starch, can also access this starch to support their own metabolism Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

animals also store glucose in a polysaccharide called glycogen it is highly branched humans and other vertebrates store glycogen in liver and muscles but only have about a one day supply Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings Insert Fig. 5.6b - glycogen Fig. 5.6b

glucose is the primary monomer used in polysaccharides 1 key difference among polys develops from 2 possible ring structures of glucose ring forms differ in whether the OH group attached to the number 1 C is fixed above (beta glucose) or below (alpha glucose) the ring plane Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings Fig. 5.7a

Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings Fig. 5.7 starch = a poly of alpha glucose monomers

structural polys form strong building materials cellulose = a major component of the tough wall of plant cells also a polymer of glucose monomers, but using beta rings Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings Fig. 5.7c

polymers built w/ alpha glucose form helical structures polymers built w/ beta glucose form straight structures this allows H atoms on one strand to form H bonds with OH groups on other strands groups of polymers form strong strands, microfibrils, that are basic building material for plants (and humans) Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

Fig. 5.8

enzymes that digest starch cannot hydrolyze the beta linkages in cellulose Any ingested cellulose passes through digestive tract and is eliminated in feces as “insoluble fiber” and abrades the intestinal walls and stimulates the secretion of mucus some microbes can digest cellulose to its glucose monomers through the use of cellulase enzymes many eukaryotic herbivores (ex: cows and termites) have symbiotic relationships w/ cellulolytic microbes Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

another important structural polysaccharide is chitin, used in the exoskeletons of arthropods (including insects, spiders, and crustaceans) it is similar to cellulose, except that it contains a nitrogen- containing appendage on each glucose pure chitin is leathery, but the addition of calcium carbonate hardens the chitin it also forms structural support for cell walls of many fungi Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings Fig. 5.9