Metabolism: core pathways and regulation

Definition and functions of metabolism

Metabolism is the set of life-sustaining, enzyme-catalyzed chemical reactions occurring within living organisms. Its core roles include converting energy from food into a usable form for cellular processes, converting nutrients into building blocks for macromolecules (such as proteins, lipids, nucleic acids, and some carbohydrates), and eliminating metabolic waste. Metabolism also encompasses digestion and transport of substances between cells, and within cells it is often described as intermediary (intermediate) metabolism. Metabolic reactions are organized into pathways where one compound is transformed step-by-step into another, with each step typically driven by a specific enzyme. Two major functional categories are catabolism (breaking down compounds, often releasing energy) and anabolism (building complex molecules, typically consuming energy). Enzymes are crucial because they enable reactions that would otherwise not proceed efficiently, and they allow regulation of reaction rates in response to environmental changes and cellular signals, supporting growth, reproduction, structure maintenance, and adaptation.

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Intermediary metabolism and scope of reactions

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