Keywords

Activation energy

The energy required to enable a reaction to take place.

Active site

The area on an enzyme molecule to which the substrate binds.

Buffer

A substance that resists a change in pH when acid or alkali is added.

Catalyst

A substance that increases the rate of a reaction but does not take part in the reaction, and so is reusable.

Coenzyme

An organic, non-protein molecule that binds temporarily with the substrate to an enzyme active site. It is essential for enzyme activity.

Cofactor

A molecule or ion that helps an enzyme to work. It may be an inorganic ion or a coenzyme.

Competitive inhibitor

A substance that reduces the rate of an enzyme-controlled reaction by binding to the enzyme’s active site.

Denaturation

An irreversible change in the tertiary structure of a protein molecule. It leads to loss of function in most proteins.

End-product inhibition

The regulation of metabolic pathways where the last product in a sequence of enzyme-controlled reactions becomes an inhibitor of one of the enzymes earlier in the sequence.

Enzyme

Biological catalyst that speeds up metabolic reactions inside cells.

Enzyme-substrate complex

The intermediate structure formed when a substrate molecule binds to an enzyme active site.

Globular protein

Proteins with relatively spherical molecules, soluble in water, often having metabolic roles in organisms.

Induced fit hypothesis

The theory of enzyme action in which the enzyme molecule changes shape to fit the substrate molecule more closely as it binds to it.

Inhibition

The slowing of an enzyme-controlled reaction by a substance that slows or prevents the formation of enzyme-substrate complexes.

Lock and key hypothesis

The theory of enzyme action where the enzyme active site is complementary to the substrate molecule.

Metabolism

All the chemical reactions that take place inside the cells of an organism.

Non-competitive inhibitor

An inhibitor of an enzyme-controlled reaction that binds to the enzyme at an allosteric site.

Peptide bond

The covalent bond formed when amino acids are joined together in condensation reactions.

Polypeptide

A polymer consisting of many amino acid monomers covalently bonded together by peptide bonds.

Prosthetic group

A non-protein group covalently attached to a polypeptide.

Substrate

The substance that is used up in an enzyme-controlled reaction, leading to the formation of a product. It binds to the active site of the enzyme at the start of the reaction.

Turnover

Rate at which an enzyme converts substrate into product.