MathsGradeUp logoMathsGradeUp
BiologyGCSE, IGCSE & A Level

What is enzyme?

An enzyme is a biological catalyst — a protein that speeds up a specific reaction by lowering its activation energy.

Enzyme explained

The active site has a shape complementary to the substrate. The induced-fit model refines the older lock-and-key idea: the active site moulds slightly around the substrate as it binds.
Temperature and pH change the shape of the active site. Beyond the optimum, hydrogen and ionic bonds break, the enzyme denatures, and activity is lost permanently.

Key formula

enzyme + substrate → enzyme-substrate complex → enzyme + product

Worked example

Amylase breaks starch into maltose in the mouth and small intestine, working best near pH 7.

Examiner tip

Say 'denatured', not 'killed' — enzymes are molecules, not organisms, and the marking scheme rejects the word killed.

Enzyme: common questions

Why are enzymes specific?
The active site shape is complementary to only one substrate shape, so no other molecule fits and forms the complex.
Is denaturation reversible?
Usually not. Once the tertiary structure and active site are disrupted by heat, the enzyme cannot recover its function.

Related terms

Osmosis

Osmosis is the net movement of water molecules from a dilute solution to a concentrated one through a partially permeable membrane.

Photosynthesis

Photosynthesis is the process by which plants use light energy to convert carbon dioxide and water into glucose and oxygen.

Respiration

Respiration is the enzyme-controlled release of energy from glucose in every living cell, transferring it to ATP.

Practise biology on MathsGradeUp

Take enzyme from a definition to full marks with exam-board question banks, revision notes and instant step-by-step feedback from Study Coach.

Biology revision notesPractice questionsCreate a free account

Related on MathsGradeUp

Keep studying

Practise it