Anabolism

Anabolism refers to the set of metabolic processes that build complex molecules from simpler ones, consuming energy in the process. It contrasts with catabolism, which breaks down larger molecules to release energy. Anabolic pathways support growth, tissue maintenance, and storage by synthesizing proteins, nucleic acids, polysaccharides, and lipids from smaller units such as amino acids, nucleotides, monosaccharides, and acetyl-CoA.

Energy and reducing power are central to anabolic reactions. They typically require ATP and reducing equivalents such as NADPH. NADPH is generated by routes like the pentose phosphate pathway and is used in fatty acid, cholesterol, and nucleotide biosynthesis. Regulation of anabolism involves hormonal and cellular energy signals; insulin and growth hormone generally promote anabolic activity, while glucagon and cortisol favor catabolic pathways. A high cellular energy charge (high ATP and NADPH levels) favors biosynthesis, whereas energy deficit (high AMP/ADP) inhibits it.

Enzymatic control underlies anabolic biosynthesis. Biosynthetic pathways include protein synthesis on ribosomes, fatty acid and cholesterol synthesis in the cytosol, and nucleotide and vitamin biosynthesis. In plants, photosynthesis supplies ATP and NADPH to drive carbon fixation and sugar formation, linking energy capture to biosynthesis. Anabolism supports organismal growth, development, and repair, as well as storage molecule formation.

Dysregulation of anabolic processes can contribute to disease, such as impaired tissue synthesis during malnutrition or excessive anabolic activity in tumor growth. Understanding the balance between anabolic and catabolic fluxes is essential to grasping energy management and homeostasis in living systems.