Chapter 3: Chemical Reactions and Enzymes

Energy Concepts

• Energy: Capacity to do work
  • Potential Energy: Stored energy; energy of position
  • Kinetic Energy: Energy of motion
  • Conversion between potential and kinetic energy
  • Examples:
    • Concentration gradients across membranes (e.g., sodium ions)
    • Electron shell transitions

Chemical Energy

• A form of potential energy stored in chemical bonds
• Released when bonds are broken
• Used for:
  • Movement
  • Synthesis of molecules
  • Establishing concentration gradients
• Key molecules:
  • Triglycerides: Energy storage form of lipids
  • Glucose: Stored as glycogen
  • ATP: Energy currency of the cell, high-energy phosphate bonds

Forms of Kinetic Energy

• Electrical Energy: Movement of charged particles (ions)
  • Example: Nerve impulses
• Mechanical Energy: Movement due to applied force (e.g., muscle contraction)
• Sound Energy: Compression of molecules by vibration
• Radiant Energy: Electromagnetic waves (e.g., visible light)
• Heat: Measured as temperature; byproduct of metabolic processes

Laws of Thermodynamics

• First Law: Energy cannot be created or destroyed, only transformed
• Second Law: Energy transformation leads to loss of usable energy as heat

Metabolism and Chemical Reactions

• Metabolism: Sum of all biochemical reactions in organisms
  • Reactants (start) and Products (end)
• Types of Reactions:
  • Decomposition: Large molecules are broken down (catabolism)
  • Synthesis: Small units combine to form larger molecules
  • Exchange Reactions: Elements are exchanged between structures
  • Redox Reactions: Exchange of electrons; oxidation and reduction

Reaction Classification

• Exergonic: Release more energy than consumed
• Endergonic: Require energy input
• ATP Cycle: Continuous formation and breakdown of ATP
• Irreversible vs Reversible Reactions:
  • Irreversible: One-directional, net loss of reactants
  • Reversible: Can proceed in both directions, reach equilibrium

Reaction Rates

• Influenced by activation energy
• Increased by temperature, but enzymes are more efficient

Enzymes

• Enzyme Function: Catalysts that speed up reactions by lowering activation energy
• Structure: Globular proteins with specific active sites
• Enzyme-Substrate Complex: Temporary binding changes shape, lowers activation energy

Enzyme Regulation

• Cofactors and Coenzymes: Needed for enzyme activation
• Enzyme Concentration: More enzymes speed up reaction rate
• Temperature and pH: Optimal ranges for enzyme activity
• Inhibitors:
  • Competitive: Compete with substrate for active site
  • Non-competitive: Bind elsewhere, change shape of active site

Enzyme Pathways

• Metabolic Pathways: Series of enzymes where product of one is substrate for next
• Multi-enzyme Complexes: Enzymes physically linked together for efficiency

Enzyme Regulation Techniques

• Feedback Inhibition: End product inhibits pathway start
• Phosphorylation/Dephosphorylation: Addition/removal of phosphate groups to regulate activity

Practical Applications

• Enzyme inhibitors in drugs (e.g., penicillin)
• Addressing enzyme deficiencies (e.g., lactase supplements for lactose intolerance)