SACE BIOLOGY: Enzymes Summary

Enzymes: Core Concepts

• Definition: Biological catalysts, almost always proteins, speed up specific chemical reactions without being consumed.

• Mechanism: Substrates bind to an enzyme's active site, forming an enzyme-substrate complex.

• Specificity: Enzymes are highly specific; the 'lock-and-key' or 'induced-fit' model explains how active sites recognize specific substrates.

• Catalysis: Enzymes facilitate reactions by lowering the activation energy ($E_a$), promoting bond breaking and formation.

  • They bring reactants together in proper orientation.

  • They put strain on chemical bonds in the substrate.

  • Can work in cascades, spreading $E_a$ over smaller steps.

• Types of Reactions: Catalyze both synthesis (building) and breakdown reactions.

• Denaturation: Change in the active site's shape (often due to extreme temperature or pH) renders the enzyme non-functional.

• Metabolism: Encompasses all biochemical reactions, with enzymes catalyzing step-by-step pathways.

Factors Affecting Enzyme Activity

• Temperature:

  • Low temperatures: Low activity due to less molecular collision.

  • Increasing temperature: Increases activity due to more collisions.

  • Optimal temperature: Peak activity (e.g., $37^{\circ}C$ for human enzymes).

  • Above optimal: Causes denaturation, irreversible loss of active site shape.

• pH:

  • Optimal pH: Maximizes activity (varies greatly by enzyme, e.g., stomach enzymes vs. blood enzymes).

  • Deviations from optimal pH: Denatures enzymes, reducing or stopping activity.

• Inhibitors: Molecules that reduce enzyme activity.

  • Competitive inhibitors: Mimic the substrate, binding to and blocking the active site.

  • Non-competitive inhibitors: Bind to a different site on the enzyme, altering the active site's shape.

  • Important for metabolic control (e.g., end-product inhibition).

• Concentration of Reactants/Substrates:

  • Increasing substrate concentration increases reaction rate until all active sites are saturated, then rate plateaus.

• Concentration of Enzymes:

  • Increasing enzyme concentration generally increases reaction rate until enzymes are more likely to encounter each other than substrates.