3.2 Kreb's Cycle

3.2 Aerobic Respiration Kreb's Cycle

Stages of Cellular Respiration

• Glycolysis: Breakdown of glucose into pyruvate.

• Pyruvate Oxidation: Conversion of pyruvate into Acetyl CoA.

• Krebs Cycle: Series of chemical reactions to produce energy-carrying molecules.

• Electron Transport Chain: Final stage producing ATP through oxidative phosphorylation.

Kreb's Cycle History

• Discovery: Discovered by Hans Krebs in 1937.

• Nobel Prize: Awarded the Nobel Prize in Physiology or Medicine in 1953 for the discovery.

Overview of Aerobic Respiration

• Requires Oxygen: All stages except glycolysis occur in aerobic conditions.

• Key Inputs: Glucose, oxygen, and pyruvate.

• Key Outputs: Carbon dioxide, water, and energy (ATP).

• Balanced Equation:

  • C6H12O6 + 6O2 → 6CO2 + 6H2O + Energy (Chemical bonds of ATP)

The Kreb's Cycle Process

• Initiation: Acetyl CoA (2C) from pyruvate oxidation combines with oxaloacetate (4C) to form citrate (6C).

• Reactions:

  • Undergoes decarboxylation and redox reactions to regenerate oxaloacetate.

  • Key intermediates include citrate, isocitrate, and α-ketoglutarate.

  • Converts back to oxaloacetate to continue the cycle.

Krebs Cycle Stages and Intermediate Compounds

• Pyruvate (3C) reacts to form Acetyl CoA (2C).

• Citrate Formation: Acetyl CoA + Oxaloacetate → Citrate (6C).

• Major compound transformations involve NAD+ to NADH and FAD to FADH2.

Products of the Kreb’s Cycle

• Each Cycle produces:

  • 3 molecules of NADH

  • 1 molecule of FADH2

  • 1 molecule of ATP

  • 2 molecules of CO2

• The Krebs Cycle occurs twice for each glucose molecule, thus:

  • Total yield per glucose: 6 NADH, 2 FADH2, 2 ATP, and 4 CO2.