Glycolysis / Glycolytic Pathway / Aerobic Respiration: Study Notes

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Glycolysis

• Initial stage of respiration that does not require oxygen (anaerobic).
• Common to both aerobic and anaerobic respiration.
• Converts carbohydrates to a 3-carbon compound (pyruvic acid).
• Takes place in the cytoplasm.
• Universal process for energy harvesting in living organisms.

Stages of Glycolysis

1. Phosphorylation of Sugar
   • Activates sugar, making it reactive.
   • ATP is used, which will later enable ATP production.
2. Lysis
   • The 6-carbon sugar splits into two 3-carbon sugar phosphates.
   • The term "glycolysis" refers to this splitting of sugar.
3. Oxidation by Dehydrogenation
   • Each 3-carbon sugar phosphate converts into pyruvate.

• This includes:
  • • Dehydrogenation (NAD is reduced to NADH).
  • Production of 2 ATP per 3-carbon sugar phosphate.

Aspect Details

• Location: Cytoplasm
• Process: Converts carbohydrates into pyruvic acid
• Summary: 1 glucose → 2 pyruvate, 4 ATP, 2 NADH + H⁺ (Net gain: 2 ATP, 2 NADH + H⁺)

The Link Reaction

• Pyruvate is actively transported from the cytoplasm through the outer and inner mitochondrial membranes into the mitochondrial matrix.
• In the matrix, pyruvate undergoes decarboxylation and dehydrogenation and combines with coenzyme A (CoA) to form acetyl coenzyme A (acetyl-CoA). This is known as the link reaction.
• During this process, the hydrogen removed from pyruvate is transferred to NAD, reducing it to NADH.

Krebs Cycle (Citric Acid Cycle)

Summary of the Cycle

• In a single turn of the cycle:
  • Two carbons enter from acetyl CoA, and two molecules of carbon dioxide are released.
  • Three molecules of NADH and one molecule of FADH₂ are generated.
  • One molecule of ATP or GTP is produced.

Overall Summary of Cellular Respiration

1. Glycolysis
   • ATP Invested: 2 ATP
   • ATP Generated: 4 ATP (Net Gain: 2 ATP)
   • NADH: 2 NADH, yielding 4 ATP through oxidative phosphorylation.
2. Pyruvate Decarboxylation
   • NADH Generated: 2 NADH (6 ATP through oxidative phosphorylation)
3. Citric Acid Cycle
   • ATP/GTP: 2 ATP (substrate-level phosphorylation)
   • NADH: 6 NADH (yielding 18 ATP through oxidative phosphorylation)
   • FADH₂: 2 FADH₂ (yielding 4 ATP through oxidative phosphorylation)

Total ATP Yield: 36 ATP

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