Role of Enzymes

Overview of Enzymes

• Enzymes are biological catalysts.
  • Speed up chemical reactions without being consumed.
  • Regenerated by the end of the reaction if used up.
• Mostly proteins, some are RNA molecules with catalytic properties.
• Essential for biochemical reactions in living organisms.

Importance of Enzymes

• Reactions in the body can occur spontaneously but are too slow to sustain life.
• Two ways to increase reaction speed:
  1. Increasing temperature:
     • Human core temperature is 37°C.
     • A slight increase can cause sickness or death by denaturing proteins.
  2. Enzymatic catalysis:
     • Increases the reaction rate significantly (10^5 to 10^7 times faster).
     • Does not increase the quantity of product, only the rate.
     • Highly specific for their substrates.

Enzyme Function and Activation Energy

• Enzymes lower the activation energy required for reactions to proceed.
  • Delta G (ΔG): Free energy of activation.
  • Transition state: Intermediate state reactants must pass through to become products.
  • Without enzymes: High activation energy.
  • With enzymes: Lowered activation energy facilitates a quicker reaction.
• Enzymes do not change product quantity, only the speed of formation.

Enzyme Inhibition

• Inhibitors: Compounds that decrease enzymatic activity by binding to enzymes:
  • Can be reversible or irreversible.
  • Common types of reversible inhibition:
    1. Competitive inhibition:
       • Inhibitors resemble substrates and bind to the active site.
       • Only one (inhibitor or substrate) can bind to the enzyme.
       • Binding depends on inhibitor vs. substrate concentration.
    2. Pure non-competitive inhibition:
       • Inhibitor binds away from the active site.
       • Changes enzyme conformation, reducing effectiveness.
    3. Mixed non-competitive inhibition:
       • Inhibitor binds near the active site.
       • Affects enzyme-substrate affinity.
    4. Uncompetitive inhibition:
       • Inhibitor binds to enzyme-substrate complex, halting the reaction.
• Competitive Inhibition Example:
  • Enzyme binds to substrate or inhibitor exclusively.
  • Reaction proceeds only if substrate binds.

Allosteric Enzymes

• Consist of multiple subunits and show cooperative binding.
• Binding of effector molecules results in conformational changes.
  • Activators: Increase enzyme activity and reaction rate.
  • Inhibitors: Decrease enzyme activity and reaction rate.
• Allosteric enzymes don’t follow Michaelis-Menten kinetics.
• Have active sites for substrates and regulatory sites for effectors:
  • Effector binding affects enzyme kinetics i.e., rate of reaction.
  • Examples:
    • Activator: Increases affinity for the substrate.
    • Inhibitor: Changes conformation, preventing substrate binding.

Summary

• Enzymes are crucial for speeding up biochemical reactions without being consumed.
• Lower activation energy, increasing reaction rates without altering product quantities.
• Inhibition can be competitive, non-competitive, or uncompetitive.
• Allosteric enzymes are regulated by effector molecules binding to regulatory sites.

Next Lecture

• Topic: The cell as a basis of life, starting with cell theory and cell size.