Enzyme Action - A Level Biology

Introduction

• Enzymes are essential biological catalysts.
• Important at both GCSE and A-Level Biology.

Structure of Enzymes

• Tertiary Structure Proteins
  • Enzymes have a specific tertiary structure.
  • Tertiary structure is determined by the sequence of amino acids in the primary structure.
  • Determines the 3D shape and active site of the enzyme.
• Active Site
  • A small, specific, unique part of the enzyme.
  • Site where the substrate binds.
  • Complementary in shape to the substrate.
  • Forms enzyme-substrate complexes, a key term in explaining enzyme action.

Function of Enzymes

• Catalyze reactions by lowering activation energy.
• Activation Energy
  • Minimum energy needed for a reaction to occur.
  • Enzymes decrease the required activation energy.

Models of Enzyme Action

Lock and Key Model

• Concept
  • Enzyme's active site is like a lock, substrate is the key.
  • Active site is an exact, fixed shape.
  • Only the complementary key (substrate) fits into the lock (active site).
• Mechanism
  • Random collisions lead to enzyme-substrate complex formation.
  • Substrate distorts slightly, lowering activation energy.
  • Products are released; the enzyme can be reused.

Induced Fit Model

• Concept
  • Analogy of a glove and hand.
  • The active site is almost complementary and changes shape to fit the substrate.
• Mechanism
  • Active site molds around the substrate upon binding.
  • Causes strain, weakening bonds in the substrate.
  • Lowers activation energy required for the reaction.
  • Products are released; active site returns to original shape.

Accepted Model

• Induced Fit Model is the accepted model for enzyme action.
• Emphasizes the dynamic nature of the active site during reaction.

Conclusion

• Enzymes are crucial for biological reactions.
• Understanding enzyme action helps in explaining how reactions are catalyzed by lowering activation energy.