Catabolism
Catabolism is the breakdown side of metabolism, using enzyme-controlled pathways to degrade molecules and capture usable energy or building blocks.
What catabolism is
Catabolism is the collection of metabolic pathways that break molecules down. Cells use catabolic reactions to release energy, recover reusable parts, dispose of molecules, and feed other pathways with smaller intermediates.
Breakdown does not mean waste
Breaking a molecule down can be constructive for the cell. Sugars, fats, proteins, and storage molecules can be degraded into pieces that enter central metabolism. Those pieces may be oxidized for energy or redirected into new biosynthesis.
How energy is captured
Catabolic pathways often release free energy in controlled steps. Cells capture some of that energy in ATP, reduced electron carriers such as NADH, or ion gradients that can later power ATP synthase and transport.
Examples of catabolic pathways
Glycolysis breaks glucose into smaller carbon compounds. Cellular respiration can oxidize fuels to carbon dioxide and water. Fatty acid breakdown, amino-acid degradation, and fermentation are also catabolic in different contexts.
Catabolism and anabolism
Catabolism and anabolism are not independent machines. Catabolic reactions can supply energy and precursor molecules for anabolic reactions, while anabolic demand can change how much fuel the cell breaks down.
Enzymes control the pace
Catabolic pathways are enzyme-driven and highly regulated. Cells speed up or slow down particular steps according to fuel availability, oxygen, hormones, energy charge, product buildup, and the needs of growth or maintenance.
In whole organisms
In animals, catabolism includes the breakdown of dietary nutrients and stored fuels. In plants and microbes, catabolism also supports growth, repair, survival during darkness or starvation, and the use of diverse environmental energy sources.
Why it matters
Catabolism explains how cells turn stored chemical matter into usable energy and metabolic ingredients. It matters for exercise, fasting, microbial ecology, decomposition, fermentation, disease, biotechnology, and the balance between cellular breakdown and rebuilding.