Topic 3.4: Cellular Energy

Introduction to Cellular Energy

• All living things require energy for processes like:
  • Maintaining homeostasis
  • Growth and development
  • Responding to stimuli
• Energy acquisition methods:
  • Animals: Consuming organic molecules
  • Fungi: Absorbing nutrients from surroundings
  • Producers (e.g., plants): Using sunlight energy
  • Prokaryotes: Diverse methods including consumption and production

Principles of Energy Transformation

• Energy is the ability to do work or cause change
• Forms of energy include light, kinetic, thermal, gravitational, nuclear, and chemical
• Chemical Energy: Important in biological sciences
  • Formed via photosynthesis in plants
  • Used by consumers as glucose is broken down

Thermodynamics in Biology

• First Law of Thermodynamics:
  • Principle of energy conservation: Energy cannot be created or destroyed, only transferred or transformed
  • Example: Plants convert light to chemical energy
• Second Law of Thermodynamics:
  • Energy transformations are inefficient; energy is lost as heat, increasing entropy
  • Entropy (S) measures disorder; higher entropy indicates more disorder
  • Biological systems increase disorder (entropy) but do not violate the second law

Key Reactions and Pathways

• Catabolic Reactions: Breakdown of molecules; increase in entropy, negative ΔG, spontaneous
• Anabolic Reactions: Build-up of molecules; decrease in entropy, positive ΔG, non-spontaneous
• Cellular Respiration and Photosynthesis:
  • Cellular respiration: Breakdown of glucose, catabolic
  • Photosynthesis: Formation of glucose, anabolic

Free Energy and Equilibrium

• Gibbs Free Energy (G): Energy available for work
  • Negative ΔG indicates a reaction releases energy and is spontaneous
  • Positive ΔG requires energy input and is non-spontaneous
• Equilibrium in Systems:
  • In closed systems: Equilibrium halts reactions
  • In living systems: Disequilibrium maintained by active processes

Metabolic Pathways

• Complex pathways linked by reactants/products
• Cellular respiration as an example of step-wise metabolic pathways

ATP: The Energy Molecule

• ATP Structure: Adenine, ribose, and three phosphates
• ATP Hydrolysis:
  • Converts ATP to ADP and phosphate, releasing energy
  • Phosphorylation: Process where released phosphate bonds to another molecule, allowing work
  • Examples: Sodium-potassium pump, glucose breakdown, muscle contraction

Conclusion

• Phosphorylation is a key process in cellular energy management
• ATP plays a crucial role in numerous cell activities and pathways