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ProblemSet8 - base catalysis Why isn’t glycine among...

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Chem 114A Practice Problems Chapter 11: 1. Explain why enzymes are stereospecific? 2. What is an apoenzyme and hoe does it differ from a holoenzyme? Which form is active? 3. What is the relationship between vitamins and coenzymes? 4. What is the rate-determining step of an enzyme-catalyzed reaction? 5. Answer yes or no to the following questions and explain your answer. a) Can the absolute value of G for a reaction be larger than + G (free energy of activation)? b) Can + G for an enzyme-catalyzed reaction be greater than + G for the nonenzymatic reaction? c) In a two step reaction, such as the one diagrammed in Fig.11-6, must the intermediate (I) have less free energy than the reactant (A)? d) In a multistep reaction, does the transition state with the highest free energy always correspond to the rate-determining step? 6. An increase in temperature increases the rate of a reaction. How does the temperature affect + G ? 7. List the amino acid residues that are most likely to participate in general acid-
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Unformatted text preview: base catalysis. Why isn’t glycine among those listed? 8. If a protonated His residue acts as the proton donor in an acid-catalyzed enzymetic reaction, what happens to the enzyme’s activity as the pH increases to a value that exceeds the pK R of that residue? 9. The pK values of two essential catalytic residues in RNase A are 5.4 and 6.4. Which corresponds to His 12 and which to His 119? 10. What is the difference between nucleophilic catalysis and general base catalysis? 11. A good covalent catalyst is highly nucleophilic and can form a good leaving group. What structural properties support these seemingly opposite characteristics? 12. Classify each of the following groups as an electrophile or nucleophile: a) amine b) carbonyl c) cationic imine d) hydroxyl e) imidazole 13. What is the role of Zn 2+ in carbonic anhydrase? 14. How hoes lysozyme destroys bacterial cell walls?...
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ProblemSet8 - base catalysis Why isn’t glycine among...

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