Enzymes: An Overview

Enzymes are biological catalysts which are predominantly proteins.
They speed up biochemical reactions by lowering the activation energy.
They have unique three-dimensional structures making them specific to their substrate.

Types of Enzymes

Intracellular enzymes: These enzymes work within the cells which produce them.
Extracellular enzymes: These enzymes are secreted by cells and work outside these cells.

The active site of an enzyme is the region where the substrate binds.
The interaction of the enzyme’s active site with the substrate leads to the formation of an enzyme-substrate complex.
The ‘lock and key’ model and the ‘induced fit’ model are the two models explaining the enzyme-substrate interaction.

Temperature: Enzyme activity generally increases with increasing temperature, up to an optimal point, beyond which the protein denatures.
PH: Enzymes have an optimal pH at which they function best. Deviation from this optimal pH can lead to decrease in activity or denaturation.
Substrate concentration: Generally, as substrate concentration increases, the rate of reaction increases until the point at which all active sites are occupied (saturation point).

Competitive inhibitors bind to the active site of the enzyme, preventing substrate binding.
Non-competitive inhibitors bind to an allosteric site (not the active site), changing the enzyme’s shape so the substrate can’t bind.

Enzymes can be modulated by cooperative binding, where binding of one substrate molecule to an enzyme promotes binding of additional substrate molecules.
Allosteric regulation allows for modulation of enzyme activity via binding of molecules (activators or inhibitors) to allosteric sites on the enzyme.