Question

If radioactive glucose, labeled at carbon #6 with 14C, were incubated in a cell-free
liver homogenate under anaerobic conditions, which carbon in the lactate produced would be
labeled with 14C (refer to the carboxyl carbon of lactate as C1, the central carbon as C2, and the
methyl carbon as C3)? What if the glucose were labeled at carbon #3 instead? In both cases,
explain your answer.

Answer 1

Ans. When glucose undergo fermentation it forms two molecules of lactic acid.

The carboxyl carbon of one molecule of lactic acid will be labelled with C14.

On the other hand if the carbon was labelled,

Then the methyl carbon of the one molecule of lactic acid will be labelled with C14.

This can be easily interpreted with following diagram: