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) Glycolysis consists of many enzyme-catalyzed reactions, each of which extracts a small amount of energy from the glucose molecule.

Question

Quizplus · Accepted Answer

Most of the free energy available from the oxidation of glucose remains in pyruvate, one of the products of glycolysis. Only a small portion of the free energy is extracted during glycolysis, which is why only two molecules of NADH are formed. This remaining energy is extracted in subsequent stages of cellular respiration, such as the citric acid cycle and oxidative phosphorylation.

The Free Energy for the Oxidation of Glucose to CO₂