Lecture Notes: Cellular Energetics

Introduction

• Lecturer starts with a personal anecdote about a haircut, transitioning to the main topic.
• Main Topic: Cellular energetics, applicable to studying and daily energy requirements.
• Key areas to cover: Enzymes, Photosynthesis, and Respiration.

Basic Concepts of Energy

• Types of Energy in Biology:
  • Kinetic Energy: Energy of movement.
  • Heat Energy: Related to temperature; more heat implies more energy.
  • Chemical Energy: Stored in molecular bonds; potential energy for biological work.

Thermodynamics

• Definition: Science of energy transfer.
• First Law of Thermodynamics (Conservation of Energy):
  • Energy cannot be created or destroyed, only transferred.
• Second Law of Thermodynamics (Entropy):
  • Entropy (disorder) of the universe always increases.
• Thermodynamic Equation:
  • ( \Delta G = \Delta H - T \Delta S )
  • ( \Delta G ): Gibbs free energy (usable energy for work).
  • ( \Delta H ): Enthalpy (total potential energy).
  • ( \Delta S ): Entropy (disorder).
  • T: Temperature.

ATP and Reaction Coupling

• ATP (Adenosine Triphosphate):
  • Stores energy in phosphate bonds; breaking bonds releases energy.
  • Reaction Coupling:
    • Uses energy from exergonic reactions to power endergonic reactions.
    • Example: ATP breakdown helps melt ice by providing energy.

Enzymes

• Definition: Biological catalysts that speed up reactions without being consumed.
• Mechanism:
  • Active Site: Region where substrate binds.
  • Substrate: Molecule upon which an enzyme acts.
• Influences on Enzymes:
  • Temperature, pH, and presence of cofactors/coenzymes.
• Enzyme Inhibition:
  • Competitive Inhibition: Inhibitor competes with substrate for active site.
  • Non-Competitive Inhibition: Inhibitor binds elsewhere, altering structure.
  • Allosteric Regulation: Can activate or inhibit enzyme activity.
• Feedback Inhibition:
  • Product inhibits enzyme activity to prevent overproduction.

Respiration

• Purpose: Convert oxygen and glucose into ATP, CO2, and H2O.
• Steps:
  • Glycolysis: Converts glucose to pyruvate, yielding ATP and NADH.
  • Pyruvate Oxidation: Converts pyruvate to acetyl-CoA, releasing CO2.
  • Krebs Cycle: Breaks down acetyl-CoA, producing ATP, NADH, and FADH2.
  • Electron Transport Chain: Uses NADH and O2 to produce ATP via oxidative phosphorylation.
• Fermentation:
  • Anaerobic process using glycolysis to produce ATP without oxygen.

Photosynthesis

• Performed by Autotrophs: Convert light energy to glucose.
• Equation: ( \text{CO}_2 + \text{H}_2\text{O} \rightarrow \text{C}6\text{H}{12}\text{O}_6 + \text{O}_2 )
• Light-Dependent Reactions:
  • Capture energy from light, excite electrons, produce ATP and NADPH.
• Calvin Cycle (Light-Independent):
  • Uses ATP and NADPH to convert CO2 into glucose.
• Adaptations:
  • C4 Plants: Use different enzymes to avoid photorespiration.
  • CAM Plants: Open stomata at night to store CO2.

Molecular Variation

• Concept: Adaptation of molecules (e.g., chlorophyll) to different conditions.
• Example: Changes in chlorophyll ratios to optimize light absorption.

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• Conclusion: Cellular energetics is vital to understanding how organisms function and adapt energetically.