Cellular Respiration: Glycolysis and Krebs Cycle

Cellular Respiration

Glycolysis

• Definition: The process of breaking down glucose into pyruvate, producing energy.
• Location: Cytoplasm of the cell.
• Phases:
  1. Energy Investment Phase:
     • Uses 2 ATP to convert glucose into fructose-1,6-bisphosphate.
  2. Energy Payoff Phase:
     • Produces 4 ATP (net gain of 2 ATP), 2 NADH, and 2 pyruvate molecules.
• Key Enzymes: Hexokinase, Phosphofructokinase, Pyruvate kinase.
• Outcome:
  • 2 ATP (net gain), 2 NADH, and 2 pyruvate per glucose molecule.

Krebs Cycle (Citric Acid Cycle)

• Definition: Series of reactions that further break down pyruvate into carbon dioxide.
• Location: Mitochondrial matrix.
• Inputs: Acetyl-CoA (derived from pyruvate).
• Outputs:
  • 3 NADH, 1 FADH2, 1 ATP (or GTP), and 2 CO₂ per acetyl-CoA.
• Key Enzymes: Citrate synthase, Aconitase, Isocitrate dehydrogenase, and Alpha-ketoglutarate dehydrogenase.
• Cycle Turns: Each glucose results in two turns of the cycle (one for each pyruvate).
• Role: Generates high-energy electron carriers (NADH, FADH2) for the electron transport chain.

Aerobic Respiration

• Definition: The process of producing cellular energy with oxygen.
• Stages:
  1. Glycolysis: Conversion of glucose to pyruvate.
  2. Krebs Cycle: Processes pyruvate into CO₂, generating electron carriers.
  3. Electron Transport Chain (ETC):
     • Location: Inner mitochondrial membrane.
     • Uses electrons from NADH and FADH2 to pump protons (H+) across the membrane, creating a gradient.
     • ATP synthase utilizes this gradient to produce ATP from ADP and inorganic phosphate.
     • Oxygen acts as the final electron acceptor, forming water.
• Efficiency:
  • Produces up to 36-38 ATP molecules per glucose molecule.
• Importance: Provides ATP for cellular functions and is essential for energy metabolism in aerobic organisms.

Summary

• Cellular respiration efficiently converts glucose into usable energy (ATP) through glycolysis, the Krebs cycle, and the electron transport chain, with oxygen playing a crucial role in the process.

Cellular Respiration

• Definition: Process of converting glucose into ATP to fuel cellular activities.

Glycolysis

• Definition: Breakdown of glucose into pyruvate; occurs in the cytoplasm.
• Energy Investment Phase: Uses 2 ATP to convert glucose into fructose-1,6-bisphosphate.
• Energy Payoff Phase: Produces 4 ATP (net gain of 2 ATP), 2 NADH, and 2 pyruvate molecules.
• Key Enzymes:
  • Hexokinase
  • Phosphofructokinase
  • Pyruvate kinase
• Outcome: 2 ATP (net gain), 2 NADH, and 2 pyruvate per glucose molecule.

Krebs Cycle (Citric Acid Cycle)

• Definition: Series of reactions that further break down pyruvate into carbon dioxide; occurs in the mitochondrial matrix.
• Inputs: Acetyl-CoA (derived from pyruvate).
• Outputs:
  • 3 NADH
  • 1 FADH2
  • 1 ATP (or GTP)
  • 2 CO₂ per acetyl-CoA
• Key Enzymes:
  • Citrate synthase
  • Aconitase
  • Isocitrate dehydrogenase
  • Alpha-ketoglutarate dehydrogenase
• Cycle Turns: Two turns for each glucose molecule (one for each pyruvate).
• Role: Generates high-energy electron carriers (NADH, FADH2) for the electron transport chain.

Aerobic Respiration

• Definition: Process of producing cellular energy with oxygen.

• Stages:

  • Glycolysis: Conversion of glucose to pyruvate.
  • Krebs Cycle: Processes pyruvate into CO₂, generating electron carriers.
  • Electron Transport Chain (ETC):
    • Location: Inner mitochondrial membrane.
    • Uses electrons from NADH and FADH2 to pump protons (H+) across the membrane, creating a gradient.
    • ATP synthase utilizes this gradient to produce ATP from ADP and inorganic phosphate.
    • Oxygen acts as the final electron acceptor, forming water.

• Efficiency: Produces up to 36-38 ATP molecules per glucose molecule.

• Importance: Provides ATP for cellular functions and is essential for energy metabolism in aerobic organisms.