3958710661

3958710661 - Chemistry 6921 Exam 2 Fall Semester 2009...

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Chemistry 6921 Exam 2 Name________Key______________ Fall Semester 2009 1-10 (2 points each). True or False. If the statement is false, change the underlined portion of the statement to make it true. ___F___1. In competitive inhibition, the inhibitor binds directly to enzyme-substrate complex but not to the free enzyme. uncompetitive ___T___2. The side chains of the amino acid residues with pKs in or near physiological pH range are capable of participating in the general acid and/or base catalysis. ___F___3. Proximity and orientation catalysis involves rate acceleration through the transient formation of an enzyme-substrate covalent bond. covalent ___T___4. Metal ions like Na + , K + , or Ca 2+ usually play structural but not catalytic roles in metalloenzymes. ___T___5. One of the most important mechanisms of enzymatic catalysis is the binding of the transition state to an enzyme with greater affinity than the corresponding substrates or products. ___F___6. Diisopropylphosphofluoridate (DIPF) reacts with all serine residues of chymotrypsin. Only Ser195, the amino acid residue in the active site __F____7. Catalytic triad of chymotrypsin includes Tyr, Phe, and Trp residues. Ser, His, Asp ___F___8. Most proteolytic enzymes are synthesized as shorter inactive precursors known as zymogens. longer inactive precursors ___T___9. Assumption of steady state in the enzyme kinetics means that the concentration of enzyme-substrate complex stays constant because the rate of synthesis of ES is equal to the rate of its consumption over the course of the reaction. ____F__10. Catalytically perfect enzymes have catalytic efficiency in the range of 10 8 -10 9 mM -1 s -1 , 10 8 -10 9 M -1 s -1
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11. (12 points) Aspartate transcarbamoylase (ATCase) converts aspartate and carbamoyl phosphate to carbamoyl aspartate and is activated cooperatively by these substrates. A bisubstrate analog, PALA, inhibits the enzyme at high concentrations, but activates the enzyme at low concentrations. Explain these phenomena. ATCase is a multisubunit enzyme. Binding PALA to one of the enzyme’s subunit forces the
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3958710661 - Chemistry 6921 Exam 2 Fall Semester 2009...

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