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5/23/12 Biological Macromolecules • • Large molecules that perform many important biological functions – Carbohydrates – Lipids – Proteins – Nucleic Acids Many are polymers – Large molecule that is made of repeating units of identical or similar subunits – Each subunit=monomer Biological Polymerization • Accomplished through covalent bonding • Often takes place via dehydration reactions which result in the release of a water molecule/bond formed • Process can be reversed by hydrolysis which breaks bonds by the addition of water • • Carbohydrates Includes sugars and polymers of sugars Used for variety of functions – Energy-simple sugars – Storage of energy-starches – Structural components-cellulose and chitin Monosaccharides • Simple sugars=monomers Usually have chemical composition of CxH2xOx • Can exist as chains or rings (usually rings in solution) • Monosaccharides combine to form disaccharides • Sugar Classification • Sugars may be classified by: – Number of carbons in chain – Location of carbonyl group – Position of side groups from asymmetrical carbon Disaccharide Formation • Disaccharides are formed by the dehydration reaction between two monosaccharides • Bond between monosaccharides is called the glycosidic linkage – Linkage may occur between different different carbons • • Storage Carbohydrates Polysaccharides=many monomers in one polymer – Glucose is most common monomer used Starches =plants use for energy storage – Amylose is unbranched chain of glucose monomers • Glycogen=animals use glycogen as medium-term energy storage – Glycogen is highly-branched polymer of glucose monomers – Cells contain enough glycogen for approximately one day’s activity Structural Carbohydrates • Cellulose – Most abundant organic compound on earth – Plants use cellulose as structural component of cell walls – Most animals cannot digest • Certain bacteria can degrade cellulose • Cows and termites have symbiotic relationship w/ bacteria – Fiber in your diet usually means cellulose • Not digested so acts as a mechanical cleansing mechanism as it passes through the intestines – Comprises polymerized units of glucose Starch vs Cellulose • Both use 1-4 glycosidic linkage of glucose • Starch uses configuration of glucose – Results in helical molecule • Cellulose uses B configuration of glucose – Forms linear strands that interact to form fiber bundles Structural Carbohydrates 2 • Chitin – Comprises polymer of N-acetylglucosamine (NAG) • Similar to glucose but possesses a nitrogen-containing side chain • Major component of insect and crustacean exoskeleton • Major component of fungal cell walls • Can be flexible or made rigid by interacting with calcium – Cross-links the structure
