2006finalkeyparson-young - Biochemistry 441 Key Final Exam...

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Biochemistry 441 Final Exam March 13, 2006 Key 1. Draw the structure of arginine. 2. The rate of fatty acid synthesis by an enzyme preparation from liver cells is higher in bicarbonate buffer than in phosphate buffer. Why? The rate-limiting step for fatty acid synthesis is carboxylation of acetyl-CoA to form malonyl-CoA, which requires CO 2 or bicarbonate. (In phosphate buffer, the bicarbonate concentration depends on the small amount of dissolved CO 2 in equilibrium with the atomosphere.) 3. Indicate by numbers 1-5 the order in which the following steps usually occur in photosystem II: __2__ Transfer of energy to the reaction center __5__ Diffusion of a reduced quinone to the cytochrome- b 6 f complex __1__ Excitation of antenna chlorophyll molecule by light __3__ Transfer of an electron to a pheophytin __4__ Proton uptake by a quinone 4 . A. In the structure below, indicate by one or more arrows the carbon or carbons that is/are donated by a derivative of tetrahydrofolate, and circle the atom or atoms that is/are derived from glycine. B . What is this compound? GDP NH 3 + NH 2 + H 2 N-C-NH-CH 2 CH 2 CH 2 C-CO 2 - H C O NH C C C N HC N NH 2 N OH H OH O O-P-O-P-O-CH 2 O O - - O O - N 10 -formylTHF N 10 -formylTHF
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In a “fluorescence recovery after photobleaching” (FRAP) experiment, a membrane protein in human cells was labeled with a fluorescent tag. At the arrow in the chart below, a strong pulse of light was focused to a spot on the surface of an individual cell, bleaching the fluorescent molecules in this region. The curves show the fluorescence from the bleached region as a function of time when the experiment was performed at 34, 36, 38 or 40 o C. A. Why does much of the fluorescence gradually reappear after the bleaching pulse? The laser pulse bleaches only the molecules in a small region. Unbleached molecules then diffuse into this region from elsewhere in the membrane. The rate of recovery of the fluorescence is a measure of the rate of lateral diffusion of the protein in the membrane. B. How would you explain the abrupt change in the rate of the recovery between 36 and 38 o C? The rate of diffusion of the protein increases with the fluidity of the membrane, which depends on the phosopholipid composition and the amount of cholesterol in the membrane. The fluidity of biological membranes typically increases in a cooperative “melting” transition at a temperature somewhat below the growth temperature, although this transition can be broadened by cholesterol and lipid rafts. Human cells grow optimally at ~38 o , so the transition seen in the experiment is in the expected range. 6 . What is the minimum number of photons of yellow-green (570 nm) light that chloroplasts must absorb for each molecule of O 2 they generate during continuous illumination? Explain briefly. Time (seconds)
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This note was uploaded on 02/02/2010 for the course BIOCHEMIST Biochem 44 taught by Professor Parson,young during the Winter '10 term at University of Washington.

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2006finalkeyparson-young - Biochemistry 441 Key Final Exam...

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