MCAT Biological and Biochemical Foundations of Living Systems Practice Exam 2026 - Free MCAT Practice Questions and Study Guide

In the process of gluconeogenesis, the body synthesizes glucose from non-carbohydrate precursors, particularly during periods of fasting or intense exercise. The key substrates utilized in this metabolic pathway include glycerol, lactate, and glucogenic amino acids, all of which can be converted into intermediates that feed into the gluconeogenic process.

Glycerol 3-phosphate and lactate can be derived from triglycerides and anaerobic respiration, respectively, and are crucial for the production of glucose. Similarly, glucogenic amino acids, which can be converted into pyruvate or other intermediates of the Krebs cycle, also serve as important substrates for gluconeogenesis.

In contrast, glucose itself is not a substrate for gluconeogenesis. The process of gluconeogenesis is essentially the reverse of glycolysis, but glucose is the final product formed rather than a precursor. Therefore, while glucose is an end product of gluconeogenesis, it does not act as a substrate in this process. This distinction highlights why glucose is not considered an important substrate for gluconeogenesis.