Lecture on Cellular Respiration: Glycolysis and Intermediate Step

Introduction

• Focus on the beginnings of cellular respiration: Glycolysis and Intermediate step.
• Summary reaction equation involves two reactants, three arrows (stages), and two products: CO2 and H2O.
• Mitochondrion (singular of mitochondria) is key to the process.
• Three main stages: Glycolysis, Citric Acid Cycle, Oxidative Phosphorylation.

Glycolysis

• Location: Occurs in the cytoplasm.
• Purpose: Breakdown of glucose (C6H12O6) into two pyruvate molecules.
• Energy Output: Produces a small amount of ATP and NADH (electron carrier).

Steps in Glycolysis

1. Glucose to Pyruvate:

   • Glucose (C6) is broken into two 3-carbon pyruvates.
   • Bonds involved in the breakdown release electrons captured by NAD+ (forming NADH).
   • NAD+ gains electrons (reduction), glucose loses electrons (oxidation).

2. ATP Production:

   • Energy Investment: 2 ATP used to phosphorylate glucose.
   • Energy Payoff: 4 ATP produced via substrate-level phosphorylation.
   • Net gain: 2 ATP.

3. Enzymes: Each step is catalyzed by specific enzymes (not memorized for this class).

Key Terms

• Isomerization: Conversion between glucose 6-phosphate and fructose 6-phosphate.
• Substrate-Level Phosphorylation: Direct transfer of phosphate to ADP from a substrate.
• Oxidation-Reduction Reactions: Coupled reactions where electron transfer occurs.

Intermediate Step

• Transition from Cytoplasm to Mitochondrion:

  • Pyruvate enters the mitochondria.
  • Each pyruvate (3C) releases one CO2, transforming into Acetyl-CoA (2C).

• Coenzyme A:

  • Facilitates the entry of acetyl group into the citric acid cycle.
  • Analogous to a tool (e.g., screwdriver) necessary for specific function.

Key Reactions

• Decarboxylation: Removal of CO2 from pyruvate.
• Formation of Acetyl-CoA: Pyruvate + Coenzyme A → Acetyl-CoA.
• NAD+ to NADH:
  • NAD+ is reduced to NADH (electron carrier), involves electron gain.
  • Oxidation of pyruvate results in electron loss.

Review

• Reactants/Products of Glycolysis: Glucose → 2 Pyruvate, 2 ATP, 2 NADH.
• Reactants/Products of Intermediate Step: 2 Pyruvate → 2 Acetyl-CoA, 2 CO2, 2 NADH.

Conclusion

• Glycolysis and Intermediate step efficiently prepare the reactants for the Citric Acid Cycle in the mitochondrion.
• Students should review diagrams and understand reactants/products from them.
• Part 2 will cover the Citric Acid Cycle and oxidative phosphorylation.

Study Tips

• Refer to diagrams for understanding the flow of reactions.
• Focus on understanding the processes rather than memorizing all intermediate compounds.