Enzymes

⚗️ Enzymes as Catalysts

Enzymes are proteins that act as biological catalysts — they speed up reactions without being used up.

• Each enzyme has a specific 3D active site that only fits one substrate (or very similar molecules)
• Lock-and-key model — substrate fits precisely into the active site like a key into a lock
• Induced fit model — active site changes shape slightly when substrate binds, giving a tighter fit
• Enzyme-substrate complex forms → products released → enzyme unchanged and reusable

🌡️ Effect of Temperature

Temperature affects enzyme activity in a predictable pattern.

• Low temperature: slow rate (low kinetic energy, fewer collisions per second)
• Increasing temperature: rate increases (more kinetic energy)
• Optimum temperature (~37°C for human enzymes): maximum rate
• Above optimum: denaturation — hydrogen bonds and ionic bonds break, active site changes shape permanently, substrate cannot bind

⚗️ Effect of pH, Inhibitors

• Each enzyme has an optimum pH (e.g. pepsin pH 2; salivary amylase pH 7; trypsin pH 8)
• Extreme pH denatures the enzyme by changing active site shape
• Competitive inhibitors — similar shape to substrate; compete for active site; block substrate entry; effect reduced by more substrate
• Non-competitive inhibitors — bind to allosteric site (different from active site); change active site shape; substrate cannot bind; not reversed by more substrate