BCH 100, Winter 2009 WH #3 6 points LECTURES # 7-9 due Wed. January 28, 2009, 2 pm Read carefully and give just one answer per question. 1. (1 pt) For longer term (not just moment to moment) but still reversible regulation of enzyme activity that can be coordinated systemically by hormone action on multiple cells and tissues, cells use a) allosteric regulation by small molecule (homotropic & heterotropic effector) concentrations. b) covalent modification/demodification, e.g., phosphorylation/dephosphorylation. c) zymogen activation. d) none of the above 2. (1 pt) Suppose that an enzyme that requires an active site Cys thiol group to be in the unprotonated form (thiolate anion, R-S – ) to act as a nucleophile. If the pKa of that specific thiol is 8.3, what percent of all the enzyme molecules would have their Cys thiol in the active form at pH 8.0? (NOTE: this asks for a percent of the total , not just a ratio.) a) 0 % c) 33% e) 67% g) 100% b) 10% d) 50% f) 90% 3. (1 pt) In the catalytic mechanism of chymotrypsin, the primary role of the active site serine
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