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Chapter 6

Chapter Quiz

Chapter Quiz

This activity contains 26 questions.

	Level I In an ionic reaction, an electron-rich species is referred to as:   an electrophile. a nucleophile. a carbonium ion. a free radical. a transition state. None of the above.

	Level I Of what class is the following reaction?   nucleophilic attack electrophilic attack direct displacement free radical reaction dehydrogenation

	Level I Identify the activation energy on the following energy diagram.   A B C D E

	Level I In enzyme catalysis, the proximity effect refers to:   The approach of a substrate to an enzyme. Close contacts made by neighboring enzyme monomers. The effective increase in concentration of reacting species by binding to the active site. The increase in energy produced by bringing two atoms closer than their van der Waals distance. None of the above.

	Level I Which of the following properties is not characteristic of enzymes?   Stabilize transition states. Alter the equibrium distribution of substrate and product. Reduce the activation energy. Often use acid-base catalysis. Vary widely in catalytic efficiency.

	Level I Cleavage of bacterial cell wall polysaccharide is an example of:   a dehydrogenation. a free radical reaction. acid-base catalysis. direct displacement. None of the above.

	Level I Catalysis by lysozyme displays all of the following except:   substrate distortion. stabilization of an unstable reaction intermediate. transition state stabilization. covalent catalysis. All of the above are characteristic of lysozyme.

	Level I Enzymes accelerate reaction rates by:   altering the equilibrium of a reaction. increasing the temperature of a solution. increasing entropy. decreasing the energy of the transition state. lowering the energy of the products.

	Level I In chymotrypsin, the tetrahedral substrate intermediate is stabilized by:   His-57. Ser-195. neighboring backbone amine hydrogens. All of the above. None of the above.

	Level I Compared with the rate of the forward reaction, enzymes:   decrease the rate of the reverse reaction. have no effect on the rate of the reverse reaction. increase the rate of the reverse reaction.

	Level II How many transition states would you expect to find in the reaction described by the following free energy diagram?   1 2 3 4 5

	Level II Select the energy diagram that correctly illustrates the effects of enzyme catalysis on a unimolecular reaction:

	Level II Which of the following amino acids is most likely to be involved in binding pyruvate to the enzyme pyruvate dehydrogenase?   aspartate glutamate lysine tyrosine None of the above.

	Level II Which of the following amino acids is most ideally suited to participate in acid-base catalysis near neutral pH?   aspartate glutamate lysine histidine arginine

	Level II Which of the following depicts the correct pH dependence of lysozyme activity?

	Level II A characteristic of the active site of lysozyme that is a common feature of many enzymes is:   the presence of both an uncharged and a charged carboxylate amino acid in the active site. an active site that is a cleft near the surface of the protein. a pH optimum of about 5. cleavage of polysaccharides. its relatively small size.

	Level II A common feature of all serine proteases is:   cleavage of proteins on the carboxyl side of serine residues. tight binding of -p-toluenesulfonyl phenylalanine chloromethyl ketone (TPCK). autocatalytic activation of zymogen precursors. the presence of a ser-his-asp catalytic triad at the active site. lack of substrate cleavage site specificity.

	Level II Which of the following proteases would be most affected by the inhibitor, p-toluenesulfonyl-lysine-chloromethyl-ketone (TLCK)?   trypsin chymotrypsin elastase chymotrypsinogen proelastase

	Level II You've just stumbled upon a mutant form of trypsin that cleaves proteins at glutamate and aspartate residues, rather than arginine or lysine residues. Which of the following point mutations could account for this change in specificity?   Arg -> Glu Lys -> Asp His -> Arg Asp -> Lys Asp -> Glu

	Level II Predict the effect on the pKa of a glutamate residue by placing it in a hydrophobic environment (i.e. buried in a protein).   The apparent pKa would be lower than in free solution. The apparent pKa would be higher than in free solution. The apparent pKa would not be different than in free solution.

	Level III Referring to the pH titration curve shown below, indicate how many ionizable residues, and which amino acids, are involved in catalysis by this enzyme.   1, aspartate 1, lysine 2, cysteine, lysine 2, cysteine, histidine 3, aspartate, cysteine, histidine 3, aspartate, histidine, lysine

	Level III Which of the steps in the reaction sequence catalyzed by triose phosphate isomerase is affected in the glutamate-aspartate mutant (p. 169) generated by Dr. Jeremy Knowles and colleagues?   substate binding catalysis product release All of the above. None of the above.

	Level III Which of the following energy diagrams depicts a mutant enzyme that has a Km for its substrate greater than the wild-type enzyme? Wild-type enzyme:   None of the above.

	Level III Which of the following compounds would you choose as an antigen, if you wished to raise catalytic antibodies that mimic lysozyme?   (GlcNAc-MurNAc)2 (GlcNAc-MurNAc)3

	Level III Site-directed lysozyme mutants that contain polar, rather than nonpolar, residues near Glu-35 would have a pH optimum:   greater than the wild-type enzyme. less than the wild-type enzyme. identical to the wild-type enzyme. shifted to low pH and would now have a second optimum at high pH.

	Level III The catalytic mechanism of serine proteases is:   sequential, ordered sequential, random ping-pong a mixture of sequential and ping-pong None of the above.

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