thumb|Schematic diagram showing anabolism and catabolism
Anabolism ( ) is the set of metabolic pathways that construct macromolecules like DNA or RNA from smaller units. These reactions require energy, known also as an endergonic process. Anabolism is the building-up aspect of metabolism, whereas catabolism is the breaking-down aspect. Anabolism is usually synonymous with biosynthesis.
Pathway
Polymerization, an anabolic pathway used to build macromolecules such as nucleic acids, proteins, and polysaccharides, uses condensation reactions to join monomers. Macromolecules are created from smaller molecules using enzymes and cofactors.
thumb|Use of ATP to drive the endergonic process of anabolism.|alt=|495x495px
Energy source
Anabolism is powered by catabolism, where large molecules are broken down into smaller parts and then used up in cellular respiration. Many anabolic processes are powered by the cleavage of adenosine triphosphate (ATP). Anabolism usually involves reduction and decreases entropy, making it unfavorable without energy input. The starting materials, called the precursor molecules, are joined using the chemical energy made available from hydrolyzing ATP, reducing the cofactors NAD<sup>+</sup>, NADP<sup>+</sup>, and FAD, or performing other favorable side reactions. Occasionally it can also be driven by entropy without energy input, in cases like the formation of the phospholipid bilayer of a cell, where hydrophobic interactions aggregate the molecules.
Cofactors
The reducing agents NADH, NADPH, and FADH<sub>2</sub>, regulating the metabolism of protein, carbohydrates, and fats.
Photosynthetic carbohydrate synthesis
Photosynthetic carbohydrate synthesis in plants and certain bacteria is an anabolic process that produces glucose, cellulose, starch, lipids, and proteins from CO<sub>2</sub>. It is the process of converting pyruvate into glucose. Pyruvate can come from the breakdown of glucose, lactate, amino acids, or glycerol. The gluconeogenesis pathway has many reversible enzymatic processes in common with glycolysis, but it is not the process of glycolysis in reverse. It uses different irreversible enzymes to ensure the overall pathway runs in one direction only.
The balance between anabolism and catabolism is sensitive to ADP and ATP, otherwise known as the energy charge of the cell. High amounts of ATP cause cells to favor the anabolic pathway and slow catabolic activity, while excess ADP slows anabolism and favors catabolism.
Etymology
The word anabolism is from Neo-Latin, with roots from , "upward" and , "to throw".