The free energy for the oxidation of glucose to CO2 and water is -686 kcal/mol and the free energy for the reduction of NAD+ to NADH is +53 kcal/mol. Why are only two molecules of NADH formed during glycolysis when it appears that as many as a dozen could be formed?
A) Most of the free energy available from the oxidation of glucose is used in the production of ATP in glycolysis.
B) Glycolysis is a very inefficient reaction, with much of the energy of glucose released as heat.
C) Most of the free energy available from the oxidation of glucose remains in pyruvate, one of the products of glycolysis.
D) There is no CO2 or water produced as products of glycolysis.
E) Glycolysis consists of many enzymatic reactions, each of which extracts some energy from the glucose molecule.

Question

Quizplus · Accepted Answer

During glycolysis, the majority of the free energy available from the oxidation of glucose remains in the two pyruvate molecules produced. The two molecules of NADH are formed in the process of oxidizing glyceraldehyde-3-phosphate, each of which produces only one molecule of NADH. While it appears that more NADH could be formed during glycolysis, the remaining reactions in the pathway do not contain steps that generate additional molecules of NADH. Additionally, while glycolysis is not a completely efficient process, the majority of the energy is not released as heat but rather remains in the pyruvate.

The Free Energy for the Oxidation of Glucose to CO2