18. Oxaloacetate uniformly labeled with \"C (i.e, with equal amounts of \"C in e

Question

18. Oxaloacetate uniformly labeled with "C (i.e, with equal amounts of "C in each of its carbon After a single pass through the citric acid atoms) is condensed with u cycle back to oxaloacetate, what fraction of the original radioactivity will be found in the oxaloacetate? nlabeled ace tyl-CoA. A) All B) 1/2 C) 1/3 D) 2/3 E) 1/4 19. The two moles of CO2 produced in the first turn of the citric acid cycle have their origin in the: A) carboxyl and methylene carbons of oxaloacetate B) carboxyl group of acetate and a carboxyl group of oxaloacetate. C) carboxyl group of acetate and the keto group of oxaloacetate. D) two carbon atoms of acetate E) two carboxyl groups derived from oxaloacetate. The reaction A+BChasao"of-20 kl/mol at 25° C. Starting under standard conditions one can predict that: 20. A) at equilibrium, the concentration of B will exceed the concentration of A. B) at equilibrium, the concentration of C will be less than the concentration of A. C) at equilibrium, the concentration of C will be much greater than the concentration of A or B. D) C will rapidly break down to A + B E) when A and B are mixed, the reaction will proceed rapidly toward formation of C

Explanation / Answer

Ans 18 : B) 1/2

Acetyl Co a is a two carbon compound , which when added to 4 carbon compound oxalo acetate converts it into a six carbon compound citrate. It undergoes one complete round of citric acid cycle to give 2 molecules of CO2 , which were originally a part of oxaloacetate. The carbon from acetyl Co A , now become the part of carbon back bone of oxalo acetate.

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