Imagine that a mannose labeled at C3 with 14C entered glycolysis (as discussed i
ID: 66910 • Letter: I
Question
Imagine that a mannose labeled at C3 with 14C entered glycolysis (as discussed in the Ch. 12 slides) and proceeded through until two pyruvates are formed? Where will the labeled carbon appear? Question 6 options:
-The carboxylate carbon of both pyruvates
-The carboxylate carbon of one of the pyruvates
-The ketone carbon of both pyruvates
-The ketone carbon of one of the pyruvates
-The methyl carbon of both pyruvates
-The methyl carbon of one of the pyruvates
-None of the carbons of the pyruvates; the labeled carbon will have been lost as CO2.
Explanation / Answer
Ans: The carboxylate carbon of one of the pyruvates
Mannose and glucose are epimers at carbon-2. The mannose said in the question is labelled at C-3, and therefore, even after entering glycolysis, has the labelled carbon at the same position. During glycolysis, this carbon becomes the carbonyl carbon of one of the glyceraldehyde-3-P, and thus, is the Carbonyl carbon of one of the pyruvates.