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

  • 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.

Factors Affecting Enzyme Activity

  • 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).

Enzyme Inhibition

  • 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.

Cooperative Binding and Allosteric Regulation

  • 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.