Lecture Notes: Energy Basics

Introduction

• Energy is crucial to understanding cellular respiration and photosynthesis.
• Cells need energy for various processes:
  • Movement of materials within the cell (requires energy, motor proteins)
  • Entire cell movement (e.g., protists)
  • Cell division
  • Molecular transport, especially against concentration gradients (active transport)
  • Certain chemical reactions require energy input.

Types of Energy

• Potential Energy:
  • Stored energy; sources include chemical bonds and concentration gradients.
  • Covalent bonds (especially nonpolar) store significant energy (glucose vs. water).
• Kinetic Energy:
  • Energy of motion; includes motion, light, and heat.

Covalent Bonds and Energy

• Nonpolar Covalent Bonds (e.g., C-H bonds):
  • High potential energy.
  • More prevalent in lipids, making them energy-rich.
• Polar Covalent Bonds (e.g., H2O):
  • Lower potential energy compared to nonpolar bonds.

Energy in Chemical Reactions

• Endergonic Reactions:
  • Require energy input, reactants have less energy than products.
• Exergonic Reactions:
  • Release energy, reactants have more energy than products.
• Reaction Coupling:
  • Uses exergonic reactions to drive endergonic reactions.

Metabolism

• Sum of all chemical reactions in an organism.
• Metabolic Pathways:
  • Multi-step reactions requiring enzymes.
  • Examples: cellular respiration and photosynthesis.

Photosynthesis vs. Cellular Respiration

• Photosynthesis:
  • Anabolic (building complex molecules), endergonic (requires energy input from the sun).
  • Converts CO2 and H2O to glucose and O2.
• Cellular Respiration:
  • Catabolic (breaking down molecules), exergonic (releases energy from glucose).
  • Converts glucose and O2 to CO2 and H2O.

Laws of Thermodynamics

• First Law: Energy is never created or destroyed, only changes form.
• Second Law: Energy usage increases disorder (entropy increases).

Redox Reactions

• Oxidation: Loss of electrons (or hydrogen).
• Reduction: Gain of electrons (or hydrogen).
• Related to cellular respiration and photosynthesis processes.

Phosphorylation

• Transfer of a phosphate group, involving energy transfer.
• ATP (adenosine triphosphate): energy currency of the cell.
• Exergonic Process: ATP hydrolysis releases energy.
• Endergonic Process: ATP synthesis (adding phosphate to ADP) requires energy.
• Energy sources: food, concentration gradients, and sunlight (in photosynthesis).

Conclusion

• Understanding these energy concepts is critical for subsequent lectures on cellular respiration and photosynthesis.