Test 2 Review - Biochemistry Enantiomers

Exam II Review 1.) Match each term with its description: a.Enantiomers b. Cellulose c. Lectins d. Glycosyltransferase e. Epimers f. starch g. Carbohydrates h. Proteoglycan i.Mucoprotein j. glycogen 1. Has the molecular formula (CH2O)n 2. Monosaccharides that differ at a single asymmetric carbon atom 3. The storage form of glucose in animals 4. The storage form of glucose in plants 5. Glycoprotein containing glycosaminoglycans 6. The most abundant organic molecule in the biosphere 7. N-Acetlygalactosamine is a key component of this glycoprotein 8. Carbohydrate binding proteins 9. Enzymes that synthesize oligosaccharides 10. Stereoisomers that are mirror images of each other 2.) Determine whether each phrase describes starch, glycogen, or cellulose: a. A major storage form of glucose in plants b. Not digestible in humans c. Made up of two glucose polysaccharides: amylose and amylopectin d. Major storage form of carbohydrates in animals 3.) Examine the five sugar structures below to answer the following questions: Which of these sugars: a. Contain or are pentoses? b. Contain or are ketoses? c. Contain the same monosaccharides? Name the monosaccharides. d. Contain a b -anomeric carbon? e. Is sucrose? 4.) Draw the structure of the disaccharide glycosyl a-1,6-galactose in b anomeric form. 5.) True or false: The double bonds in naturally occurring fatty acids tend to be cis. 6.) Some triacylglycerols are used for fuel storage in both plants and animals. The triacylglycerols from plants are often liquid at room temperature, whereas those from animals are solid. Suggest some chemical reasons for this difference. 7.) Which of the following statements regarding simple Michaelis-Menten enzyme kinetics are correct? a. The maximal velocity, Vmax, is related to the maximal number of substrate molecules that can be Òturned overÓ in unit time by a molecule of enzyme. b. Km is expressed in terms of reaction velocity (ex./ mol s-1 ). c. Km is the dissociation constant of the enzyme-substrate complex. d. Km is the concentration of substrate required to achieve half of Vmax. e. Km is the concentration of substrate required to convert half the total enzyme into the enzyme substrate complex. 8.) What is the significance of kcat/Km? 9.) What is a pseudo-first order reaction? 10.) The graph shows the plot of Vo vs [S]. for two different enzymes that catalyze the same reaction. The two enzymes have the same Km, Vmax, and turnover number. a. Compare the change in [S] required to increase activity from 20% to 80% maximum. b. Which enzyme provides a more sensitive way of controlling flow of metabolites down a metabolic pathway? Explain. 11.) Which answers (a-e) below make a true statement about free energy in the context of enzyme-substrating binding? The change in free energy when an enzyme binds to a substrateÉ a. Arises from many weak intermolecular interactions b. Contributes to the catalytic efficiency of the enzyme c. Is more negative when an incorrect substrate is bound d. Becomes more positive as the transition state of the reaction develops e. Becomes more negative the more tightly the enzyme binds to the substrate 12.) If the Km of an enzyme for its substrate remains constant as the concentration of the inhibitor increases, what can be said about the mode of inhibition? \ 13.) The alkoxide group on chymotrypsin that attacks the carbonyl oxygen of the peptide bond of the substrate arises from which amino acid side chain? a. Aspartate b. Histidine c. Serine d. Threonine e. Tyrosine 14.) Why is histidine a particularly versatile amino acid residue in its involvement in enzymatic reaction mechanisms? 15.) Place slash marks at the sites where you would expect chymotrypsin to cleave the following peptide: Lys-Gly-Phe-Thr-Tyr-Pro-Asn-Trp-Ser-Tyr-Phe 16.) Which of the following statements are false? a. The oxygen dissociation curve of myoglobin is sigmoidal, whereas that of hemoglobin is hyperbolic. b. The affinity of hemoglobin for O2 Is regulated by organic phosphates, whereas the affinity of myoglobin for O2 is not. c. Hemoglobin has a higher affinity for O2 than does myoglobin d. The affinity of both myoglobin and hemoglobin for O2 is independent of pH. 17.) Hemoglobin is a tetrameric protein consisting of two a and two b polypeptide subunits. The structure of the a and b subunits are remarkably similar to that of myoglobin. However, at a number of positions, the hydrophilic residues in myoglobin have been replaced by hydrophobic residues in hemoglobin. a. How can this observation be reconciled with generalizations that hydrophobic residues fold into the interior of proteins? b. In this regard, what can you say about the nature of the interactions that determine the quaternary structure of hemoglobin?