Oxaloacetate uniformly labeled with ¹⁴C (i.e., with equal amounts of ¹⁴C in each of its carbon atoms) is condensed with unlabeled acetyl-CoA. After a single pass through the citric acid cycle back to oxaloacetate, what fraction of the original radioactivity will be found in the oxaloacetate?

Question

Quizplus · Accepted Answer

In the citric acid cycle, two carbon atoms from acetyl-CoA are introduced into the cycle by condensing with oxaloacetate to form citrate. As the cycle progresses, two carbon atoms are released as CO2. Since the original oxaloacetate was uniformly labeled, and two of its four carbons are lost as CO2, half of the original radioactivity remains in the regenerated oxaloacetate.

Oxaloacetate Uniformly Labeled with 14C (I

Oxaloacetate Uniformly Labeled with ¹⁴C (I