Biology Chapter 6: Cellular Respiration

6.1 Glycolysis

• Purpose: Breaks down glucose into two pyruvate molecules, producing ATP and NADH.
• Location: Cytoplasm.
• Phases:
  • Energy Investment Phase: Consumes 2 ATP molecules.
  • Energy Payoff Phase: Produces 4 ATP molecules and 2 NADH.
• Major Products:
  • 2 Pyruvate
  • 2 NADH
• Net Gain: 2 ATP

6.2 Fermentation

• Mechanism: Occurs when oxygen is unavailable. Regenerates NAD⁺ from NADH to allow glycolysis to continue. Produces lactate in animals or ethanol and CO₂ in yeast/plants.
• Purpose: Ensures ATP production during anaerobic conditions.

6.3 Krebs Cycle (Citric Acid Cycle)

• Purpose: Oxidizes acetyl-CoA to CO₂, generating NADH and FADH₂. These carry high-energy electrons to the Electron Transport Chain (ETC).
• Location: Mitochondrial matrix.
• Key Molecules Involved:
  • Reactants/Inputs:
    • Acetyl-CoA (from pyruvate oxidation)
    • NAD⁺ (electron carrier)
    • FAD (electron carrier)
    • ADP + Pi
  • Products/Outputs:
    • 3 NADH (per acetyl-CoA)
    • 1 FADH₂ (per acetyl-CoA)
    • 1 ATP (via substrate-level phosphorylation)
    • 2 CO₂ (per acetyl-CoA)
• Key Points:
  • Per Acetyl-CoA (1 Cycle): 3 NADH, 1 FADH₂, 1 ATP, and 2 CO₂ are produced.
  • Per Glucose Molecule (2 Acetyl-CoA, meaning 2 turns of the cycle): 6 NADH, 2 FADH₂, 2 ATP, and 4 CO₂ are produced.
  • NADH and FADH₂ are essential for transferring high-energy electrons to the ETC for ATP generation.

6.4 Electron Transport Chain (ETC) and Oxidative Phosphorylation

• Purpose: Uses electrons from NADH and FADH₂ to create a proton gradient for ATP synthesis.
• Location: Inner mitochondrial membrane.
• Energy and Molecule Flow:
  • Protons are pumped into the intermembrane space, creating a gradient.
  • Electrons move through protein complexes (I-IV).
  • ATP synthase uses the gradient to convert ADP + Pi into ATP.
  • Oxygen acts as the final electron acceptor, forming water.

6.5 Comparison of Photosynthesis and Cellular Respiration

• Photosynthesis:
  • Location: Chloroplasts
  • Converts light energy into chemical energy (glucose).
  • Key Processes: Light-dependent reactions and Calvin Cycle.
• Cellular Respiration:
  • Location: Mitochondria
  • Converts glucose into usable energy (ATP).
  • Key Processes: Glycolysis, Krebs Cycle, ETC.
• Similarities: Both involve energy transformations and electron carriers.
• Differences: Photosynthesis stores energy while respiration releases it. They have opposite reactants and products.

6.6 Internal and External Factors Affecting Rates

• Photosynthesis:
  • Internal factors: Chlorophyll concentration and enzyme activity.
  • External factors: Light intensity, CO₂ concentration, and temperature.
• Cellular Respiration:
  • Internal factors: Enzyme levels and substrate availability.
  • External factors: Oxygen levels and temperature.
• Predictions: High light/CO₂ levels increase photosynthesis. Low oxygen inhibits aerobic respiration. Extreme temperatures disrupt enzyme function in both processes.