Energy and Enzymes - Chapter 8 Notes

Chapter Overview

• This chapter covers the role of energy and enzymes in biochemical reactions.

Energy in Chemical Reactions

• Energy: Capacity to cause change.
  • Kinetic Energy: Energy of motion (e.g., thermal energy).
  • Potential Energy: Stored energy based on position or configuration (e.g., chemical energy).
• Reaction Types:
  • Synthesis
  • Decomposition
  • Single Replacement
  • Double Replacement

Thermodynamics

Laws of Thermodynamics

1. First Law: Energy is conserved; it cannot be created or destroyed, only transformed.
2. Second Law: Every energy transfer increases disorder (entropy) in the universe.

Enthalpy (H)

• Total energy in a molecule, including potential energy in bonds and kinetic energy relating to pressure and volume.
• Exothermic Reactions: Release heat (ΔH < 0).
• Endothermic Reactions: Absorb heat (ΔH > 0).

Entropy (S)

• Measures disorder in a system.
  • ΔS (+): Products are less ordered (increased disorder).
  • ΔS (-): Products are more ordered (decreased disorder).

Gibbs Free Energy (G)

• Predicts if reactions are spontaneous or non-spontaneous:
  • Spontaneous Reaction: ΔG < 0
  • Non-Spontaneous Reaction: ΔG > 0
• Gibbs Free Energy Equation: \Delta G = \Delta H - T\Delta S
  • where T = Temperature in Kelvin.

Coupled Reactions

• Energetic Coupling: Uses energy from exergonic reactions to drive endergonic reactions.
  • Example: ATP hydrolysis can drive endergonic processes like transport or mechanical work.

ATP (Adenosine Triphosphate)

• Main energy currency of the cell, storing and providing energy for cellular processes.
• Energy is released upon hydrolysis of the terminal phosphate group to ADP, yielding -7.3 kcal/mol.

Types of Work Utilizing ATP

1. Transport Work: Phosphate group transfer alters shape of transport proteins.
2. Mechanical Work: ATP binds to motor proteins causing movement.
3. Chemical Work: ATP phosphorylates substrates to activate them for reactions.

Important Reactions and Processes

• Redox Reactions: Involve transfer of electrons (e.g., oxidation is loss of electrons, reduction is gain).
• Redox and phosphorylation are mechanisms of energetic coupling.
• ATP hydrolysis example in driving endergonic reactions: ATP transfers a phosphate to a substrate, turning it into a phosphorylated intermediate, facilitating the reaction.

Summary of Key Concepts

• Enzymes lower activation energy, speeding up reaction rates.
• Energetic coupling allows cells to perform work using energy from spontaneous reactions to fuel non-spontaneous processes.