Question

Acetyl-CoA labeled with C, as shown, can enter the citric acid cycle. Assuming all the acetyl-CoA enters the cycle... 1. What fraction of the label will be present in oxaloacetate at the end of one turn of the cycle? 14 2. Which carbons in the oxaloacetate formed by one turn of the cycle would contain the radioactive label? C4 C3 C2 Ci .What fraction of the original radiolabel present in the acetyl-CoA will be present in oxaloacetate at the end of two turns of the citric acid cycle? H2

Answer 1

Acetyl CoA is the two carbon structure with Co-enzyme A fraction. When it entered to the TCA cycle the the acetyl group attached at the carbonyl carbon of oxaloacetate as -CH₂-COO^- fashion. Later in the cycle two carbon eliminates as CO2 during the cyclic metabolic pathway but that are not these same two carbon as these two carbons are C1 and C2 as numbered in the picture here. If another cycle repeats with same kind of acetyl coA then the C3 and C4 are the bottomed carbon to left as it is and new two carbon comes in next cycle to form oxaloacetate.

1) Only the Carbon (C) of CH3 from acetyl CoA will be present in oxaloacetate at the end of one turn of the cycle.

2) C2 in the oxaloacetate formed by one turn of the cycle would contain the radioactive level.

3) After the end of two turns of TCA cycle the CH2 (C3 in the given structure) will be retained after first cycle and Carbon (C of C2 in given structre) of CH3 will be retained from second cycle.