Enzymes & Biochemical Reactions Vocabulary

The sum of all chemical reactions occurring within a living organism that maintain life, including both the breakdown of molecules for energy and the synthesis of molecules needed for cellular functions.

Metabolism

Processes in which reactants are transformed into products through the breaking and forming of chemical bonds, either releasing or absorbing energy in the process.

Chemical Reactions

Refers to metabolic reactions that break down complex molecules into simpler ones, releasing energy in the process. (e.g., cellular respiration breaking down glucose into CO₂ and water) — "Catabolism = breaking down"

Catabolic

Refers to metabolic reactions that build up complex molecules from simpler ones, requiring an input of energy. (e.g., protein synthesis, building DNA) — "Anabolism = building up"

Anabolic

The minimum amount of energy required to initiate a chemical reaction; the energy needed to break the bonds of reactants so a reaction can proceed. Enzymes lower this energy barrier.

Activation Energy

The starting material(s) in a chemical reaction that are consumed or transformed; in biology, the substrate specifically refers to the molecule that binds to an enzyme's active site to be acted upon.

Reactant/Substrate

The new molecule(s) formed as a result of a chemical reaction after reactants/substrates have been transformed.

Product

A type of reaction that absorbs energy (heat) from its surroundings, meaning the products have more energy than the reactants. The reaction requires a net input of energy. (endo = "within/taking in")

Endothermic

A type of reaction that releases energy (heat) into its surroundings, meaning the products have less energy than the reactants. The reaction gives off a net amount of energy. (exo = "outside/releasing")

Exothermic

A biological catalyst — almost always a protein — that speeds up chemical reactions in living organisms by lowering activation energy, without being consumed or permanently altered in the process.

Enzyme

Any substance that increases the rate of a chemical reaction by lowering activation energy without being used up or permanently changed by the reaction. Enzymes are the biological version of catalysts.

Catalyst

The specific region on an enzyme where the substrate binds and the chemical reaction takes place; its shape is complementary to the substrate, following the "lock and key" or "induced fit" model.

Active Site

The process by which an enzyme (or protein) loses its normal three-dimensional shape due to extreme changes in temperature, pH, or other environmental conditions, causing it to lose its function because the active site is altered or destroyed.

Denaturation