ABSTRACT
Metabolism involves interrelated contributions from mitochondrial function and insulin signaling, the biology of time, cycling of energy sensors and the family of nuclear hormone receptors, the stress response, diet, and the gut microbiome. Louis Pasteur showed that glucose fermentation to lactic acid by the anaerobic glycolysis pathway is suppressed in the presence of oxygen. Metabolic pathways may be categorized as either catabolic or anabolic. Catabolic pathways degrade large molecules into simpler ones, such as the breakdown of macronutrients from food sources into smaller units. Conversely, anabolic pathways coalesce smaller molecules into larger ones with the associated creation of chemical bonds using the energy captured by catabolic pathways. The central physiological purpose of metabolic pathways is to provide the bioenergetic needs of the body. Ketogenesis is the formation of ketone bodies in liver mitochondria. It occurs when the production of acetyl CoA exceeds what can be utilized in the tricarboxylic acid cycle.
