Enzymes

Introduction

• Enzymes are substances that control chemical reactions in the human body.
• Discovered in 1833 by Ancel Mépièm.
• Speed up biochemical reactions by modifying substrates.
• Highly selective and specific in their action.

Mode of Action

• Enzymes increase reaction rates by lowering activation energy.
• Bind substrates at an active site where bond-breaking and forming occur.
• Active sites are specific in size, shape, and chemical behavior.

Active Site

• Unique to particular substrates due to specific amino acid arrangement.
• May include a non-protein component called a cofactor:
  • Cofactors: Metal ions or organic molecules (coenzymes) that assist enzyme activity.
  • Apoenzyme: Inactive enzyme, requires a coenzyme to become a functional holoenzyme.

Models of Enzyme Action

Lock and Key Hypothesis

• Substrate fits precisely into the enzyme's active site like a key in a lock.

Induced Fit Hypothesis

• Enzyme changes shape to bind substrate more tightly after initial binding.

Environmental Effects on Enzyme Function

Temperature

• Optimal enzyme function at 37°C.
• Deviation affects chemical bonds, potentially denaturing the enzyme.

pH

• Affects the active site as amino acids are acidic or basic.
• Extreme pH can denature enzymes.

Enzyme Concentration

• Increasing concentration boosts reaction rate until saturation.

Substrate Concentration

• Up to a saturation point, more substrate increases reaction rate.

Inhibition of Enzyme Activity

Competitive Inhibitors

• Bind to active site, preventing substrate binding.

Non-Competitive Inhibitors

• Bind elsewhere on the enzyme, altering its shape and function.