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BIBC102 Midterm key 2002

BIBC102 Midterm key 2002 - METABOLIC BIOCHEMISTRY Immo E...

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METABOLIC BIOCHEMISTRY Winter 2002 Immo E. Scheffler MIDTERM EXAM - ANSWERS All answers are to be written into the Blue Book. Leave the first inside page blank for scoring. There are 11 questions. Make sure that each answer is clearly identified with the question number at the top or left side of the page. Useful Information: Avogadro's number: 6.02 x 10 23 molecules / mole 1 Faraday = 96,494 Coulomb / mole = 96,494 Joules / Volt / mole Gas constant (R) = 8.31 Joules K -1 mol -1 = 1.987 cal K -1 mol -1 = 0.082 liter atm K -1 mol -1 1 calorie = 4.184 Joules ********************************************************************************** QUESTION 1 (12 min) The following table from your textbook lists a variety of coenzymes; some of which have not been covered in class. A series of structures are given below. Identify the structure by its name (from the Table 8-2), and give an example of a reaction in which the coenzyme is involved. The reaction requires only the names of substrates and products, not their structural formulae. A) the cofactor shown in thiamine pyrophosphate ; it is required in decarboxylation reactions, for example in the formation of ethanol and CO 2 from pyruvate. B) the cofactor is nicotinamide adenine dinucleotide (NAD + ), used in a variety of oxidation/reduction reactions, for example the oxidation of glyceraldehyde 3-P to 1,3 bis- phosphoglycerate (with inorganic phosphate from the medium) The lactate dehydrogenase or pyruvate dehydrogenase reactions are also acceptable. C) the cofactor is pyridoxal phoshate ; so far we have seen it appear in the glycogen phosphorylase reaction.
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QUESTION 2 (8 min) a) For an enzyme obeying Michaelis-Menten kinetics a plot of initial rate vs. substrate concentration yields a characteristic curve. Give the algebraic expression describing this curve (in terms of [S], K M , v max ), and explain how such data allow one to estimate K M quite readily. By measuring the rates at various substrate concentrations up to very high values, one can obtain V max from the asymptote. A horizontal line at 1/2 V max intersects the experimental curve at Km, i.e. when [S] is equal to K m we observe half of the maximal velocity. b) In the same diagram contrast the behavior described in (a) with a curve one would obtain for an enzyme exhibiting allosteric behavior. (no algebra or formulae required) The curves become distinctly S- shaped, and different curves are obtained with different concentrations of effector.
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QUESTION 3 (12 min) There are four boxes below labeled A - D. a) match them in pairs, i.e. describe which kinetic curves correspond to which type of inhibition b) characterize (name) the types of inhibition shown A represents competitive inhibition and it matches the curves shown in D ; B represents uncompetitive inhibition and it matches the curves shown in C c) give a short (one or two sentences) explanation for the observation that all the lines intersect in one point on the Y-axis in figure D.
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