Question

In a hypothetical situation in which there is no pyruvate carboxylase activity in an aerobic mammalian cell, what would happen if substantial amounts of TCA cycle intermediates are suddenly withdrawn as biosynthetic precursors (to support anabolism)?

Answer 1

In a cell lacking pyruvate carboxylase, if TCA cycle intermediates are used up for anabolism, the TCA cycle cannot continue without replenishment (anaplerosis), leading to reduced ATP production.

Step-by-step explanation:

In the absence of pyruvate carboxylase activity, the cell would face a challenge as it could not perform anaplerosis, which is the process of replenishing TCA cycle intermediates. Without this activity, a situation where substantial amounts of TCA cycle intermediates are suddenly withdrawn for anabolism would lead to a depletion that cannot readily be compensated. As a result, the TCA cycle would slow down or stop, affecting ATP production among other things. The inability to synthesize oxaloacetate from pyruvate would mean that any acetyl CoA formed cannot proceed through the TCA cycle, ultimately leading to a reduction in energy production and potential accumulation of acetyl CoA, which could be diverted into other metabolic pathways like lipid synthesis.