Enzymes Notes

Energy and Chemical Reactions

  • Exergonic Reactions

    • Definition: Reactions that release energy.

    • Characteristic: Products have less chemical energy than the reactants.

    • Example: AB + CD 🡪 AC + DB + energy

    • This implies a negative change in free energy: ext{ΔG} < 0.

  • Endergonic Reactions

    • Definition: Reactions that absorb energy.

    • Characteristic: Products have more chemical energy than the reactants.

    • Example: AB + CD + energy 🡪 AC + DB

    • This implies a positive change in free energy: ext{ΔG} > 0.

  • Activation Energy (EA)

    • Definition: The minimum amount of energy required to initiate a chemical reaction.

    • Source: Often supplied as heat from the surroundings.

  • Catalysts

    • Definition: Substances that decrease the activation energy required to start a reaction.

    • Function: Speed up the reaction without being consumed in the process.

The Energetics of Chemical Reactions

  • Potential Energy in Chemical Reactions

    • Example of Rolling a Boulder Up a Hill:

    • Requires energy input.

    • At the top, the boulder has high potential energy, indicating products possess more energy than the reactants.

  • Example of Rolling a Boulder Down a Hill:

    • The boulder releases energy as it descends.

    • At the bottom, it has lower potential energy, indicating products possess less energy than the reactants.

Self-Quiz on Energetics

  • Examples of Biological Processes:

    • Photosynthesis: An endergonic process

    • Reaction: 6 ext{CO}2 + 6 ext{H}2 ext{O} + ext{energy}
      ightarrow ext{C}6 ext{H}{12} ext{O}6 + 6 ext{O}2

    • Aerobic Respiration: An exergonic process

    • Reaction: ext{C}6 ext{H}{12} ext{O}6 + 6 ext{O}2
      ightarrow 6 ext{CO}2 + 6 ext{H}2 ext{O} + ext{energy}

Chemical Reactions

  • Activation Energy (EA)

    • Definition: The initial energy needed to start a chemical reaction.

    • Its Source: Often provided in the form of heat from the surroundings.

The Effect of Enzymes on Reaction Rate

  • Progress of the Reaction

    • Reactants to Products

    • Comparison of reactions with and without an enzyme.

    • The EA without enzyme is higher than the EA with enzyme.

    • The change in free energy ( ext{ΔG}) remains unaffected by the enzyme.

  • Enzyme Function

    • Enzymes catalyze reactions by reducing the activation energy barrier.

Feedback Inhibition

  • Definition: A regulatory mechanism in which the end product of a metabolic pathway inhibits an earlier step in the pathway.

  • Function: Prevents overproduction of the pathway's end products, maintaining homeostasis and efficiency.