Becker's World of the Cell 9th Edition by Lewis Kleinsmith, Jeff Hardin, Gregory Paul Bertoni

Exercise 5

Completing the Pathway. In each of the following cases, complete the pathway by indicating the structures and order of the intermediates.
(a)The conversion of citrate to a-ketoglutarate by Reactions TCA-2 and TCA-3 involves as intermediates not only isocitrate but also molecules identified (but not shown in Figure 10-8)as aconitate and oxalosuccinate. Illustrate the pathway from citrate to a-ketoglutarate by showing the structures and order of all three intermediates.
(b)Synthesis of the amino acid glutamate can be effected from pyruvate and alanine by a metabolic sequence that illustrates the amphibolic role of the TCA cycle. Devise such a pathway, assuming the availability of whatever additional enzymes may be needed.
(c)If pyruvate-2- 14 C (pyruvate with the middle carbon atom radioactively labeled)is provided to actively respiring mitochondria, most of the radioactivity will be incorporated into citrate. Trace the route whereby radioactively labeled carbon atoms are incorporated into citrate, and indicate where in the citrate molecule the label will first appear.