problem set 3 key

problem set 3 key - Problem Set 3 BIBC 100 1. Under certain...

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Problem Set 3 BIBC 100 1. Under certain conditions, peptide bond formation is more thermodynamically more favorable than peptide bond hydrolysis. Would you expect chymotrypsin to catalyze peptide bond formation? Why? Yes, because an enzyme decreases the activation energy barrier for both the forward and reverse directions of a reaction. 2. Substrates and reactive groups in an enzyme’s active site must be precisely aligned in order for a productive reaction to occur. Why, then, is some conformational flexibility also a requirement for catalysis? The enzyme’s conformation must be flexible enough to allow substrates access to the active site, to stabilize the changing electronic structure of the transition state, and to accommodate the reaction products. 3. Peanut oil contains a high percentage of lipid acyl chains with only one double bond whereas vegetable oil contains a higher percentage of acyl chains with more than one double bond. During a cold spell, the peanut oil freezes whereas the vegetable oil remains liquid. Explain why. Each double bond in an acyl chain produces a “kink” in the molecule, meaning that the fatty acids don’t pack together as well. So the more double bonds, the more “kinks”. Less energy is required to disrupt the forces of fatty acid chains that have more kinks, so this type of molecule will melt at a lower temperature. Therefore, the vegetable oil with more double bonds has a lower melting point and does not freeze. 4. Predict which one of the following organisms will have the highest percentage of unsaturated fatty acid chains in their membranes. Explain your answer. A. Antarctic fish B. Desert iguana C. Human being D. Polar Bear E. Thermophilic bacterium Antarctic fish, which are cold-blooded, live in freezing waters. In order to maintain an appropriate fluidity of their membranes under such extreme conditions, they require a higher proportion of unsaturated fatty acid chains in their membranes. Polar bears also live in extreme cold, but they are warm-blooded and maintain a
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This note was uploaded on 12/07/2011 for the course BIBC 102 taught by Professor Price during the Spring '02 term at UCSD.

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problem set 3 key - Problem Set 3 BIBC 100 1. Under certain...

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