Question

A fasting animal is fed palmitic acid that has a 14C-labeled carboxyl group. The animal's liver glycogen becomes 14C labeled although there is no net increase in the amount of this substance present. (a) Briefly describe the pathways whereby the glycogen could become 14C labeled. Explain how hexose monophosphate pool intermediates become 14C labeled starting with this radiolabeled fatty acid even though even chain fatty acids are not gluconeogenic. (b) How does the glycogen become radiolabeled from the palmitic acid, and especially under fasting conditions (low blood Glc)? Be sure to fully explain your answer.

Answer 1

Ans. A labelled palmitic acid enters the cycle as a labelled acetyl CoA. The formation of acetyl coenzyme A is acheived by loss of two carbon atoms and which further yields to labelled oxaloacetate. Thus there will be no net synthesis of oxaloacetate to achieve the better synthesis of glucose and glycogen. The glycogen will become radiolabelled as the labelled carbon won't be eliminated as the labelled carbon dioxide.