Final Answer:
Most of the free energy released during the oxidation of glucose in glycolysis is utilized in the production of ATP. Thus the correct option is D. Most of the free energy available from the oxidation of glucose is used in the production of ATP in glycolysis.
Step-by-step explanation:
Glycolysis is the initial stage of cellular respiration, where glucose is broken down into pyruvate. The free energy change for the oxidation of glucose to CO₂ and water is -686 kcal/mol, while the free energy change for the reduction of NAD⁺ to NADH is 53 kcal/mol. However, not all the potential NADH molecules are formed during glycolysis. The key to understanding this lies in the fact that the majority of the free energy released during glucose oxidation is utilized in the synthesis of ATP.
During glycolysis, two molecules of NADH are produced for each molecule of glucose. This occurs in two steps: one in the conversion of glyceraldehyde-3-phosphate to 1,3-bisphosphoglycerate, and the other in the conversion of 3-phosphoglycerate to 2-phosphoglycerate. Both reactions involve the reduction of NAD⁺ to NADH. The remaining potential NADH molecules that could be formed are bypassed due to the energy demands of ATP synthesis in glycolysis.
In glycolysis, two ATP molecules are consumed, but four ATP molecules are produced, resulting in a net gain of two ATP molecules. This indicates that a significant portion of the free energy from glucose oxidation is utilized in the production of ATP, explaining why only two molecules of NADH are ultimately formed during glycolysis.
Thus the correct option is D. Most of the free energy available from the oxidation of glucose is used in the production of ATP in glycolysis.