Gluconeogenesis is the metabolic pathway through which glucose is synthesized from a non-glucose (carbohydrate) precursors including pyruvate, lactate, and amino acids. Pyruvate and Lactate: The precursor of gluconeogenesis is primarily pyruvate. Pyruvate is the end product of glycolysis which can be further metabolized to either acetyl CoA or lactate. The conversion of pyruvate to these products depends on tissue type, ATP status, and regulatory effector molecules. The conversion of pyruvate to acetyl CoA is an irreversible step that is catalyzed by the enzyme pyruvate dehydrogenase that occurs mainly in oxidative tissues such as the liver, cardiac muscle. In contrast, the conversion of pyruvate to lactate is a reversible step catalyzed by lactate dehydrogenase that occurs mainly in non-oxidative tissues such as red blood cells. The lactate dehydrogenase is also present in skeletal muscle that converts pyruvate to lactate during vigorous exercise. Figure 1 : Fates of Py...