Metabolism

biology

Definition

Metabolism

Metabolism is the set of chemical reactions by which a living system builds and breaks down biomolecules to extract energy and assemble its own structure. It partitions into two coupled directions:

$$\text{metabolism}=\underset{\text{break down, release energy}}{\underbrace{\text{catabolism}}}\cup \underset{\text{build up, consume energy}}{\underbrace{\text{anabolism}}}.$$

Catabolism degrades substrates $S$ into simpler products $P$ with a negative free-energy change $\Delta G<0$, releasing energy; anabolism uses that energy to drive the synthesis of complex molecules from simpler precursors with $\Delta G>0$. The two are linked by a shared currency — most often ATP — so that energy released in one reaction is spent in another. The reactions are enzyme-catalysed and together constitute the chemistry by which life maintains itself against entropy.