Question

The first two reactions of gluconeogenesis are required to reverse reaction 10 (or the last reaction) of glycolysis. How many ATP equivalents are used by these first two reactions of gluconeogenesis? The answer is not 4.

Answer 1

Glycolysis is a process of breakdown of glucose molecule in a series of 10 steps in the cytoplasm of the cell to produce pyruvate which takes part in the Krebs cycle in mitochondria for energy production. Gluconeogenesis is a reverse process of glycolysis in which pyruvate is converted back into glucose and is primarily used in storage purposes. The phosphoenolpyruvate is converted into pyruvate in the last step of glycolysis with a production of 1 molecule of ATP. ADP ATP Phosphoenolpyruvate Pyruvate In the process of gluconeogenesis, the pyruvate molecule is converted back into phosphoenolpyruvate in two steps which involve the use of one molecule of ATP and GTP per molecule of pyruvate and oxaloacetate respectively. Since pyruvate is a three- carbon molecule and glucose is a six-carbon molecule, so two molecules of pyruvate are fused together in the process to yield one molecule of glucose. 2x Pyruvate 2x ATP 2x ADP 2x Oxaloacetate 2x GTP 2x GDP

2x Phosphoenolpyruvate 9 more steps Glucose Gluconeogenesis Hence, it is understood from the chart that 2 equivalent ATPs are required for production of glucose in gluconeogenesis.