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WRITE YOUR NAME AND I.D. NUMBER LEGIBLY ON EVERY PAGE – PAGES WILL BE SEPARATED FOR GRADING! CHECK TO BE SURE YOU HAVE 6 PAGES , NAME (print): ANSWERS INCLUDING COVER PAGE. 5-digit course ID # I swear/affirm that I have neither given nor received any assistance with this exam. Signature: Date: BIOCHEMISTRY 460 FIRST HOUR EXAMINATION FORM B (white) ANSWER KEY May 30, 2007 A NON-PROGRAMMABLE CALCULATOR MAY BE USED ON THIS EXAM. No programmable calculators are permitted, and no sharing of calculators. We have a couple of spare calculators to lend in an emergency. SHOW YOUR WORK FOR ALL CALCULATIONS , AND BE SURE TO STATE UNITS OF ANY NUMERICAL ANSWERS. If the reasoning, calculations, or answer are shown anywhere other than in the space provided, make a note in the space provided and put answer on BACK OF SAME PAGE so the grader for that page will have it. USEFUL CONSTANTS : R (gas constant) = 8.315 J •mol –1 •Kelvin –1 = 8.315 x 10 –3 kJ •mol –1 •Kelvin –1 If temperature = 25 °C, absolute temperature T = 298 K (Assume this temperature unless problem states otherwise.) Use these “generic” pK a values only when no precise pK a for a specific group is given. Ionizable group in peptides and proteins Approximate ("generic") pK a (from Berg, Tymoczko & Stryer, Biochemistry , 6th ed., 2007) Potentially Useful Equations Δ G' = Δ H' T Δ S' Δ G' = Δ G°' + RTln(mass action ratio) α -carboxyl 3.1 side chain carboxyl 4.1 imidazole 6.0 α -amino 8.0 thiol 8.3 aromatic hydroxyl 10.9 ε -amino 10.8 guanidino 12.5 Michaelis-Menten Equation: V o = V max [S] [S]+K m
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Biochemistry 460, Exam #1 Form B ANSWERS NAME May 30, 2007 Last 4 digits of SID: ___________________ page 2 1. (10 pts) Suppose that the standard free energy change for the folding of the water-soluble globular enzyme below has been measured (298K): Δ G°' folding = – 25 kJ/mol unfolded protein folded protein A. (4 pts) What is the ratio of [folded] / [unfolded] protein in solution at equilibrium? (Show work.) ratio of [folded] / [unfolded] protein at equilibrium = K eq Δ G°' folding = –25 kJ/mol = – RTlnK eq = – (8.315 x 10 –3 kJ •mol –1 •K –1 )(298 K) lnK eq K eq = e Δ G°' folding / RT = e – (–25 kJ/mol) / 2.479 kJ/mol = e +10. 1 = 2.4 x 10 4 (unitless) B. (3 pts) Starting under standard conditions, would the net reaction proceed toward the left (unfolding direction) or toward the right (folding direction)? 1) toward the left (unfolding direction) *2) toward the right (folding direction) Briefly EXPLAIN your answer on the basis of the information given above (no credit for choice without appropriate explanation). Δ
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