Which of the following is NOT a starting material in gluconeogenesis?

In gluconeogenesis, the body synthesizes glucose from non-carbohydrate precursors, and certain molecules serve as substrates in this metabolic pathway. The correct choice is acetyl-CoA, which is not a starting material for gluconeogenesis.

Lactate, for example, is produced during anaerobic respiration and can be converted into pyruvate, entering gluconeogenesis at a crucial step. OAA, or oxaloacetate, is an important intermediate in gluconeogenesis that can be converted into phosphoenolpyruvate, another key substrate in the pathway. Alpha-ketoglutarate, which is involved in amino acid metabolism and the Krebs cycle, can also contribute to gluconeogenesis by being converted into succinyl-CoA and then further processed.

On the other hand, acetyl-CoA cannot be converted back into glucose. This is due to the irreversible nature of the pyruvate dehydrogenase reaction, which irreversibly commits pyruvate to the pathway leading to acetyl-CoA for energy production, rather than for gluconeogenesis. Thus, while other starting materials can be transformed into glucose through gluconeogenesis, acetyl-CoA cannot, making it the correct answer to the question.