Chem 481 F10 HW 11-19-10-1

Chem 481 F10 HW 11-19-10-1 - Name _...

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Name ______________________ Final Assignment Chem 481 F10  Dr. Steven Wood A few years ago, on the East Coast, a truckers strike caused a shortage of Twinkies. It seems that annually, 500 million of these cream filled sponge cake snacks are consumed in the U. S. The following questions are based on a snack of a Twinkie, a diet soda and a piece of beef jerky. 1. Assume that the above diet was consumed to break a prolonged fast and that the cream filling in the Twinkie was comprised of all stearic acid (C 18) triacylglycerides. Give a structural representation of stearic acid and outline how a stearic acid travels from the digestive tract to an adipocyte for storage, and then is eventually released and travels to a mitochondrion in the liver in preparation for β -oxidation (DO NOT include the steps of β -oxidation in this problem). Be sure to mention how membranes are crossed and name any necessary carriers (cytosolic or transmembrane) or cofactors. You may just use compound names if you like. 2. Show the steps necessary to convert this stearate into one molecule of “fuel” for the citric acid cycle. Include structures, indicate any necessary cofactors and indicate what type of reaction each step is i.e. dehydrogenase, oxidase, oxidation-reduction etc. and the name of the enzyme that catalyzes the final liberation of this “fuel”. 1
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If the triacylglycerides of the cream filling contained oleic acid (steric acid with a double bond at the 9 position) as well, outline any modifications to the above set of reactions necessary to convert all of the carbon atoms in this compound to citric acid cycle “fuel”. You need only show those reactions that differ from the stearate example. 4. During this fast, oxaloacetate levels in the liver have dropped. Briefly explain why they dropped. Under these conditions fatty acids would become the chief fuel source. What would happen as the acetyl- CoA levels increase as a result of the decreased levels of oxaloacetate. What are the structures of the three compounds exported from the liver to be utilized for fuel by the other tissues under these circumstances? 5. The diet soda is sweetened with aspartame (nutrasweet®) which is the methyl ester of the dipeptide, Asp-Phe. Draw out the structure of aspartame and explain why, in most individuals this sweetener would be a source of Tyr and why the diet drink carries a warning for individuals with phenylketonuria. Outline the mechanism by which the carbon atoms of Asp are converted into a major metabolic
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This note was uploaded on 04/06/2011 for the course CHEM 481 taught by Professor Wood during the Fall '10 term at BYU.

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Chem 481 F10 HW 11-19-10-1 - Name _...

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