Summary
Highlights
Enzymes are substances, primarily proteins (or sometimes RNA), that accelerate biochemical reactions by modifying specific substrates. Discovered in 1833 by Anselme Payen, enzymes are highly selective in their binding and modifying actions, a property known as specificity.
Enzymes speed up reactions by lowering their activation energy. They achieve this by binding to substrates at a specific 'active site,' facilitating chemical bond-breaking and forming processes. The active site's unique size, shape, and chemical behavior, determined by amino acid arrangement, allow it to bind specifically to a particular substrate.
Many enzymes require non-protein components called cofactors for their catalytic role. Cofactors can be temporary cations (activators), temporary organic molecules (coenzymes like vitamins), or permanently bound prosthetic groups. An inactivated enzyme (apoenzyme) combined with its coenzyme forms an active holoenzyme (Holoenzyme = Apoenzyme + Coenzyme).
Two main models describe enzyme action. The 'Lock and Key Hypothesis' suggests a perfect, unchanging fit between the substrate and the enzyme's active site, like a key in a lock. The 'Induced Fit Hypothesis' proposes that the enzyme changes shape upon substrate binding, forming an even tighter fit and fine-tuning its interaction with the substrate.
Enzyme activity is highly sensitive to environmental changes. Optimal temperature for most enzymes is 37°C; deviations can denature enzymes by affecting chemical bonds in the active site. pH fluctuations (optimal pH varies by enzyme) can also alter active site amino acids, inhibiting substrate binding and potentially leading to denaturation. Increased enzyme or substrate concentration generally increases reaction rates up to a saturation point.
Enzyme activity can be reduced or stopped by 'inhibitors,' which either block or distort the active site. Competitive inhibitors occupy the active site, preventing substrate binding. Non-competitive inhibitors attach to other parts of the enzyme, altering its shape and active site indirectly.