Gluconeogenesis is the pathway by which organisms synthesize glucose from non-carbohydrate precursors like lactate, pyruvate, glycerol, and certain amino acids. This occurs mainly in the liver and to a lesser extent in the kidneys. While some steps are reversible versions of glycolysis, three irreversible steps of glycolysis are bypassed. Specifically, pyruvate is converted to oxaloacetate then phosphoenolpyruvate through carboxylation and decarboxylation reactions requiring ATP and GTP. This generates free glucose which is an important control point, as glucose-6-phosphate is typically further processed rather than released as free glucose except in a few tissues.