1 1 Chemistry & Biochemistry 153C Name__________________________________ Fall 2002 2nd MIDTERM EXAMINATION 22 November 2002 (90 points, 3 pages, 50 minutes) PLEASE READ EACH QUESTION VERY CAREFULLY! 1. (20 points) Write out two steps in gluconeogenesis that are very similar to the first two steps in the synthesis of threonine from aspartate. Draw out the structures of each reactant and product and indicate exactly where each cofactor comes in. Write either the names or structures of the intermediates in threonine synthesis that are similar to each of the reactants and products. 2. (10 points) For the first two steps in the biosynthesis of threonine from aspartate, what factors ensure that the reaction proceeds in the direction of biosynthesis?2 2 3. (30 points) Melatonin (shown below), a hormone produced by the retina and the pineal gland of mammals, is involved in regulation of circadian rhythm. It is synthesized at night. Write out a plausible biosynthetic scheme for the synthesis of melatonin starting from essential amino acid tryptophan. For each reaction, give structures of the reactants, products and the cofactors involved. YOU DO NOT NEED TO INDICATE REACTION MECHANISMS! NCH23HCO-CH2-NH-C-CH3O Melatonin3 3 4. (30 points) Potatoes and certain cereal grains contain high levels of free asparagine and are rich in carbohydrates. Swedish scientists found that potato chips and French fries contain levels of acrylamide that are hundreds of times higher than what the EPA and WHO consider safe for drinking water. Recently, it was reported that heating glucose and asparagines at 185°C yields significant amounts of acrylamide (Nature 419, 448-449, 2002). Based on chemistry you have learned in 153C, indicate the mechanism of the first two steps of the reaction shown below by denoting electron movements with appropriate arrows. Where pertinent, indicate the resonance stabilization of intermediates. OOHOHOHOHOHNH2-CH-CH2C-NH2COO-OOHOHOHNOHNH2OC H2 NH2O+ (1) (2)O Acrylamide4
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