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Chem 135 Spring 2010 Problem Set 5 Due Thursday, March 18 at the beginning of class 1. Suppose you used yeast to brew beer using the glucose sample

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Chem 135 Spring 2010 Problem Set 5 Due Thursday, March 18 at the beginning of class 1. Suppose you used yeast to brew beer using the glucose sample indicated below, which has been 14 C-labeled at the aldehyde carbon. If ethanol fermentation is the only metabolic pathway carried out by the yeast, would you expect to find the 14 C label in the ethanol, the CO 2 , or both? Important safety note: You should NOT drink the beer from this experiment! HO OH OH OH H O OH OH ethanol fermentation which is labeled? 2 + CO 2 * * indicates 14 C label 2. Along with proteins and carbohydrates, phospholipids obtained from the plasma membrane constitute a major source of energy from food. The first step in the breakdown of phospholipids involves the hydrolysis of the ester bonds by a class of enzymes called phopholipases to form fatty acids and glycerol-3-phosphate. These metabolites are then further broken down to generate ATP. a. For a single molecule of the fatty acid shown above, provide a balanced chemical equation for its complete conversion to acetyl-CoA. b. Considering only the acetyl-CoA units obtained in part (a), how many molecules of ATP will be produced by oxidative phosphorylation in the mitochondria? Briefly show how you arrived at your conclusion. c. In addition to gaining energy by breaking down the fatty acid, energy can be derived from the catabolism of glycerol-3-phosphate. This molecule undergoes one enzymatic step and can then enter a catabolic pathway that you should remember. Indicate the product of that enzymative step and provide a reasonable arrow-pushing mechanism for its formation. 3. Poly(3-hydroxybutyrate), or PHB, is a polymer produced by certain bacteria in response to stress. This compound has been studied as a biorenewable plastic, as it has similar properties to those of polypropylene:
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a. One attractive feature of PHB as a plastic alternative is the fact that it is fully biodegradable. The first step in this process involves the hydrolysis of the ester bonds to produce the corresponding carboxylic acids. The resulting 3-hydroxybutyrate molecules are then used by microorganisms to produce ATP. Based on the mechanisms that you have learned in class, outline the metabolic steps that would be required to convert a single molecule of 3-hydroxybutyrate to ATP. You do not have to supply mechanisms with your answer. b. Based on your mechanism, how many molecules of ATP would be produced from each 3-hydroxybutyric acid monomer? Show how you arrived at your answer. c. In the forward sense, it is known that the basic building blocks of this polymer are synthesized from acetyl-CoA. By making analogies to the pathways discussed in class, propose a mechanism for the biosynthesis of this polymer from these building blocks. You do not have to supply the full structures of any cofactors that you use.
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