Catabolic

Catabolic refers to metabolic processes that break down complex molecules into simpler ones, releasing energy in the process. In contrast to anabolic pathways, which assemble larger molecules from smaller units, catabolic reactions provide energy and precursors needed for cellular activity and maintenance.

Most catabolic reactions involve hydrolysis or oxidation, releasing chemical energy stored in macromolecules. In cellular metabolism, major catabolic pathways include glycolysis (breaking down glucose to pyruvate), the conversion of pyruvate to acetyl-CoA, the tricarboxylic acid (TCA) cycle, and oxidative phosphorylation, which together generate ATP and reducing equivalents. Lipid breakdown via beta-oxidation of fatty acids yields acetyl-CoA and NADH/FADH2, while protein catabolism (proteolysis) releases amino acids that can enter various pathways or serve as energy sources when needed.

Regulation of catabolic activity is tied to energy status and hormonal signals. Low energy activates catabolic pathways through hormones such as glucagon, epinephrine, and cortisol and through rises in AMP/ADP. Insulin and other anabolic signals generally suppress catabolic breakdown. Transcriptional regulators, including FOXO and PGC-1α, influence the expression of enzymes involved in catabolic processes and mitochondrial function.

Physiological roles of catabolism include providing rapid energy for activity, maintaining blood glucose during fasting, and supplying substrates for gluconeogenesis and other pathways. In states of illness, injury, or extreme stress, uncontrolled or excessive catabolism can contribute to muscle wasting and weight loss, while impaired catabolic function can disrupt energy balance and substrate availability.