Enzymes

ENZYMES

Introduction to Enzymes

• Enzymes are proteins that function as biological catalysts.

• They increase the rate of chemical reactions without being used up in the process.

Learning Objectives

• Explain:

  • The mode of action of enzymes, including:

    • Active site

    • Enzyme-substrate complex

    • Lowering of activation energy

    • Enzyme specificity through the ‘lock and key’ hypothesis.

  • Investigate the effects of:

    • Temperature

    • pH on the rate of enzyme-catalyzed reactions.

Activation Energy

• Activation Energy (EA) is the energy barrier that reactant molecules must overcome for a reaction to occur.

• Enzymes help lower the activation energy needed, facilitating the reaction process.

Mode of Enzyme Action

• Enzymes possess active sites that have specific shapes.

• Active site: A pocket or groove on the surface of the enzyme where the substrate binds.

• The shape of the active site is complementary to the substrate, allowing specific interactions.

Enzyme-Substrate Interaction

• Enzymes and substrates are constantly in motion due to kinetic energy.

• Close proximity and proper orientation during collisions enable substrates to bind to enzymes, forming an enzyme-substrate complex.

• Enzymes strain chemical bonds within substrates, breaking and forming bonds, leading to product formation.

• Products are released when they no longer fit the active site shape.

Lock and Key Hypothesis

• Enzymes (locks) accept only specific substrates (keys) that match their active sites.

• Larger or improperly shaped substrates cannot bind, as they do not fit the enzyme's active site.

Factors Affecting Enzyme Action

Effect of Temperature

1. Increasing Temperature (0 °C to 40 °C)

   • Reaction rates increase as temperature rises due to higher kinetic energy.

   • More effective collisions occur between substrates and active sites, forming enzyme-substrate complexes.

2. Inactive Enzymes at Low Temperatures

   • Low temperatures lead to enzyme inactivity.

   • A 10 °C rise can double the rate of enzyme action.

   • Each enzyme has an optimum temperature for peak activity.

3. High Temperatures (above 40 °C)

   • Enzymes can become denatured at high temperatures, losing their functional shape.

   • The active site's shape changes, rendering it non-functional with the substrate.

Effect of pH

• Each enzyme has an optimal pH where it works best.

• Example optimal pH values:

  • Salivary amylase: pH 7

  • Pepsin: pH 2

• Generally, enzyme activity is reversible with pH changes, but extreme pH levels may cause irreversible denaturation.

Summary

• Understanding the modes of action of enzymes and factors influencing their activity is crucial for comprehending biochemical processes.