The Structure and Function of Large Biological Molecules Chapter 5 The Structure and Function of Large Biological Molecules Questions prepared by Jung Choi Georgia Institute of Technology

Which group of large biological molecules is not synthesized via dehydration reactions? polysaccharides lipids proteins nucleic acids Answer: b Concept 5.1 2

Which polysaccharide has the greatest number of branches? cellulose chitin amylose amylopectin glycogen Answer: e Concept 5.2 3

Why are human enzymes that digest starch unable to digest cellulose? Cellulose is made of amino-containing sugars that cannot be metabolized. Cellulose contains L-glucose instead of D-glucose; starch-digesting enzymes are specific for polymers of D-glucose. Cellulose has beta-glycosidic linkages; starch-digesting enzymes cleave only alpha-glycosidic linkages. Cellulose has beta-galactoside linkages that only bacterial beta-galactosidases can cleave. Cellulose fibers are covalently cross-linked; starch-digesting enzymes cannot cleave these cross-links. Answer: c Concept 5.2 4

Diversity among Biological Macromolecules Which type of biological polymer has the least diversity in physicochemical properties and structure? polysaccharides polypeptides DNA RNA Answer: c Cells use the chemically simplest polymer to store hereditary information. 5

Lipids All lipids are made from glycerol and fatty acids. contain nitrogen. have low energy content. are acidic when mixed with water. do not dissolve well in water. Answer: e This question relates to Concept 5.3. Students often answer a, confusing lipids with membrane phospholipids and fats. 6

Compared to tropical fish, arctic fish oils have Lipids Compared to tropical fish, arctic fish oils have more unsaturated fatty acids. more cholesterol. fewer unsaturated fatty acids. more trans-unsaturated fatty acids. more hydrogenated fatty acids. Answer: a This question relates to Concept 5.3. 7

Subunits If actively growing cells are fed 14C-labeled glucose, what macromolecules will become radioactive first? proteins starch nucleic acids fatty acids Answer: b This question relates to Concept 5.2. 8

Subunits and Metabolic Labeling If you want to selectively label nucleic acids being synthesized by cells, what radioactive compound would you add to the medium? 35S-labeled sulfate 32P-labeled phosphate 14C-labeled leucine 3H-labeled thymidine 14C-labeled guanine Best answer: e Phosphate would label nucleic acids but also phospholipids. Thymidine would label DNA but not RNA. Guanine would label both DNA and RNA but not phospholipids. 9

Protein Structure and Amino Acids Sickle-cell disease is caused by a mutation in the beta-hemoglobin gene that changes a charged amino acid, glutamic acid, to valine, a hydrophobic amino acid. Where in the protein would you expect to find glutamic acid? on the exterior surface of the protein in the interior of the protein, away from water at the active site, binding oxygen at the heme-binding site Answer: a This question relates to Concept 5.4 and Figure 5.22. 10

Protein Structure The sickle-cell hemoglobin mutation alters what level(s) of protein structure? primary tertiary quarternary all of the above primary and tertiary structures only Answer: d This question relates to Concept 5.4 and Figure 5.20. Formation of fibers is a form of quarternary structure, not exhibited by wild-type hemoglobin. 11

Macromolecular Structures and Bonds Ceviche is prepared by marinating fresh raw fish in citrus juice for several hours, until the flesh becomes opaque and firm, as if cooked. How does citrus juice render the seafood safe to eat? Acidic pH denatures (unfolds and inactivates) proteins by disrupting their hydrogen bonds. Citrus juice denatures proteins by disrupting their ionic bonds. Citrus juice contains enzymes that hydrolyze peptide bonds to break apart proteins. Citrus juice dissolves cell membranes by disrupting hydrophobic interactions. Answer: a This question relates to Concept 5.4. This question is intended to connect methods of food preparation and protein denaturation by disruption of bonds or interactions important for protein folding. Variants of this question could include preservation with salt or cooking by heat. 12

RNA and DNA How does RNA differ from DNA? DNA encodes hereditary information; RNA does not. DNA forms duplexes; RNA does not. DNA contains thymine; RNA contains uracil. all of the above Answer: c This question relates to Concept 5.5. RNA does encode hereditary information in RNA viruses, and RNA does form intramolecular duplexes: hairpins, pseudoknots, and other complex secondary structures. 13