Lecture Notes: Chemical Reactions in Cellular Respiration

Introduction

• Focus on chemical reactions in cellular respiration.
• Goal: Trap chemical energy from biomolecules (e.g., sugars) into ATP.
• Larger molecules (polysaccharides, fats) can store more energy.

Key Processes in Cellular Respiration

• Oxidation Reactions:

  • Involves step-by-step removal of hydrogen atoms and electrons from substrates.
  • Results in CO2 as a waste product.
  • Energy comes from breaking chemical bonds.

• Main Processes:

  1. Glycolysis
     • Over 10 chemical reactions.
     • Converts glucose and other molecules into ATP.
     • Intermediates: amino acids, simple sugars, glycerol, fatty acids.
  2. KB Cycle (Citric Acid Cycle)
     • Converts Acetyl-CoA into energy intermediates.
  3. Oxidative Phosphorylation

Metabolic Pathways

• Catabolic reactions break down molecules.
• Anabolic reactions build up molecules (reverse process).
• Exchange reactions: coupling exergonic and endergonic reactions.

Oxidation-Reduction Reactions

• Special type of exchange reaction involving electron transfer.

• Oxidation: Loss of hydrogen/electrons; molecule loses energy.

• Reduction: Gain of electrons; molecule gains energy.

• Example:

  • Glucose is oxidized to CO2.
  • Oxygen is reduced by gaining electrons.
  • Energy transfer is incremental.

Enzymes and Co-enzymes

• Dehydrogenases:

  • Remove hydrogen atoms.
  • Important in oxidation-reduction.

• Oxidases:

  • Transfer oxygen between molecules.

• Co-enzymes:

  • Vitamins are building blocks for co-enzymes.
  • NAD+ and FAD: Carriers of high-energy electrons and hydrogen.

Detailed Reaction Example

• Organic molecules undergo changes via dehydrogenases.
• Electrons from broken bonds transfer to new bonds or molecules.
• Co-enzymes like NAD+ strip electrons from hydrogen atoms.
• NAD+ Reduction:
  • Gains two electrons to become NADH.
  • Hydrogen ions remain partially detached (H+).

Energy Transfer

• Oxidation reactions transfer potential energy from chemical bonds to electrons.
• Biological systems utilize this energy to perform work, avoiding loss as heat/light.

Conclusion

• Preview of next video on ATP production through chemical reactions.