PS4-08answ - Name: _ Net ID: _ Problem Set 4 Biochemistry...

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Name: ________________________ Net ID: ______________________ Section: ________ Problem Set 4 Biochemistry 462b Spring 2008 Due Feb 15, 2007 Question 1. (4 points) Trace the course of the radioactive label in [2- 14 C] glucose through glycolysis and the citric acid cycle. (a) At what point(s) will the radioactivity be released as 14 CO 2 ? (b) How many turns of the cycle will be required for complete conversion of the radioactivity to CO 2 ? Repeat this exercise for pyruvate that is 14 C-labeled at its methyl group. Ans : The number 2 carbon of glucose will become the number 2 carbon of pyruvate, so that will be the location of the label at the end of glycolysis. As pyruvate is oxidized by the PDH complex, the number 2 carbon becomes the carbonyl carbon of the acetyl CoA, which will become the carboxyl groups (indistinguishable) of succinate in the first turn of the cycle. These two carboxyl groups are lost as CO 2 , one at the isocitrate dehydrogenase step and the other at the a-ketoglutarate dehydrogenase step, in the second turn through the cycle. Pyruvate with label in the number 3 (methyl) carbon will enter the TCA cycle with the label in the methyl group of acetyl CoA. At the succinyl CoA synthase step, the label will be mixed between the 2 methyl carbons of succinate. In the second turn through the cycle, half of the label will be divided between the two carboxyl groups of succinate and the other half will be divided between the two methyl carbons of the succinate. In the third turn through
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PS4-08answ - Name: _ Net ID: _ Problem Set 4 Biochemistry...

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