Metabolism comprises the regulated chemical reactions of living systems.
Key knowledge
Metabolism includes chemical pathways that break down substances and build biological materials. Catabolic pathways break complex molecules into simpler ones, often releasing usable energy; anabolic pathways build complex molecules and require energy input. Enzymes catalyse many of these reactions.
Conditions and scope
Individual reactions and pathways differ in their energy changes; not every breakdown step releases usable energy.
The entry describes cellular chemistry, not a personal metabolic rate, diet or treatment.
Sources · 3
References
Sources retain their recorded scope. A source link alone does not establish verification of every statement.
NIGMS's pathway, catabolism/anabolism and enzyme account; no flux or clinical measurement.
2026-10-10 · English pathway and energy distinction checked against the 2024 NIGMS article; medical examples and recommendations are excluded.
Foundational review
2026-10-10 · Fresh primary-source inspection of the complete compact record, including every statement, equation, quantity and material condition, followed by independent AI editorial review. This check does not certify all linked lessons or every passage of every cited publication.
Sources from other places
Agreement within this scope
Breakdown/synthesis pathways and enzyme-mediated cellular reactions.
A pathway can supply both energy and building materials.
Metabolism includes chemical pathways that break down substances and build biological materials. Catabolic pathways break complex molecules into simpler ones, often releasing usable energy; anabolic pathways build complex molecules and require energy input. Enzymes catalyse many of these reactions.
Carbon cycles among the atmosphere, organisms, soils, oceans and rocks. Biological processes such as photosynthesis, respiration and decomposition exchange carbon, while weathering, sediment formation and tectonic processes participate in slower geological transfers.
Photosynthesis, respiration and decomposition transfer carbon through biological processes.
Oxygenic photosynthesis uses captured light energy to support the conversion of carbon dioxide into organic compounds. Water supplies electrons and oxygen is released. This form occurs in photosynthetic plants, algae and cyanobacteria.
Metabolism includes chemical pathways that break down substances and build biological materials. Catabolic pathways break complex molecules into simpler ones, often releasing usable energy; anabolic pathways build complex molecules and require energy input. Enzymes catalyse many of these reactions.
Light-energy capture and carbon fixation supply chemical intermediates and organic compounds in photosynthetic metabolism.
In aerobic glucose breakdown, glycolysis and subsequent oxidation pathways transfer energy and electrons through carriers. Carbon dioxide is released during pyruvate oxidation and the citric acid cycle. The respiratory electron-transport chain ultimately reduces oxygen to water, and a proton gradient supports ATP synthesis.
Metabolism includes chemical pathways that break down substances and build biological materials. Catabolic pathways break complex molecules into simpler ones, often releasing usable energy; anabolic pathways build complex molecules and require energy input. Enzymes catalyse many of these reactions.
Aerobic nutrient breakdown transfers energy through electron transport to ATP production.
Cell membranes are selectively permeable. Passive transport allows net movement down the relevant gradient, through the membrane or transport proteins. Active transport couples movement against a gradient to an energy source, directly or through another gradient. Osmosis is passive net water movement across a selectively permeable membrane.
Metabolism includes chemical pathways that break down substances and build biological materials. Catabolic pathways break complex molecules into simpler ones, often releasing usable energy; anabolic pathways build complex molecules and require energy input. Enzymes catalyse many of these reactions.
Cell metabolism can supply energy for active membrane transport.
Phototrophy and chemotrophy describe energy sources; lithotrophy and organotrophy describe electron donors; autotrophy and heterotrophy describe carbon sources. These classifications can be combined and can vary with conditions. They describe metabolic strategies rather than a single taxonomic division.
Metabolic strategies specify sources for transformations.
A polymer contains covalently linked subunits derived from monomers. Polysaccharides, polypeptides and nucleic acids use different monomers and linkages; many lipids are not repeating-monomer polymers. Hydrolysis uses water to cleave a susceptible covalent linkage, as in maltose cleavage to two glucose molecules. Condensation can be represented as linkage formation with loss of a small molecule such as water, but cellular polymer synthesis often uses activated precursors rather than direct joining of free monomers with water release.
Hydrolytic cleavage is one reaction type within metabolism; a bond-cleavage label alone does not determine usable free energy.