LECTURE 15

Oxidation of Carbon Molecules
  • Process Overview:
    • Oxidation involves the transfer of electrons from carbon compounds to oxygen (O₂), the ultimate electron acceptor.
    • This results in the formation of water (H₂O) and carbon dioxide (CO₂) as waste products.
    • Free energy is released from the oxidation process.
Key Concepts in Oxidation

  • Electron Transfer:

    • Electrons are transferred in small numbers (1 or 2) during oxidation, making it a multistep process.
    • The generalized reaction for aerobic catabolism:
      Carbon Compound+O<em>2→CO</em>2+H2O+Useful Energy (ATP)\text{Carbon Compound} + O<em>2 \rightarrow CO</em>2 + H_2O + \text{Useful Energy (ATP)}

  • Oxidizing and Reducing Agents:

    • Oxidizing Agent: Accepts electrons and gets reduced.
    • Reducing Agent: Loses electrons and gets oxidized.
    • Example reactions:
    • NAD++H++2e−→NADHNAD^+ + H^+ + 2e^- \rightarrow NADH
    • NADP++H++2e−→NADPHNADP^+ + H^+ + 2e^- \rightarrow NADPH
Coenzymes Involved

  • NAD+ vs. NADP+:

    • NAD+: Used in catabolic pathways as an oxidizing agent.
    • NADPH: Used in anabolic pathways as a reducing agent; has an extra PO4PO_4 group for enzyme recognition.

  • Flavin Redox Cofactors (FAD & FMN):

    • FAD and FMN function as prosthetic groups in redox reactions:
    • FAD can be reduced:
      FAD+2H++2e−→FADH2FAD + 2H^+ + 2e^- \rightarrow FADH_2
    • Semi-reduced and fully reduced forms: FADH• (semiquinone) and FADH₂ (hydroquinone).
Stages of Catabolism
  • General Pathways:
    • Breakdown of various biomolecules (fats, polysaccharides, proteins) into Acetyl CoA.
    • Components:
    • Lipids: Fatty acids and glycerol.
    • Carbohydrates: Glucose and other sugars.
    • Proteins: Amino acids.
    • Results in energy production through the Citric Acid cycle and oxidative phosphorylation:
    • 6O<em>2+C</em>6H<em>12O</em>6→6CO<em>2+6H</em>2O+Energy (ATP)6O<em>2 + C</em>6H<em>{12}O</em>6 \rightarrow 6CO<em>2 + 6H</em>2O + \text{Energy (ATP)}
Glycolysis Overview

  • Pathway:

    • Converts glucose (C₆H₁₂O₆) into two molecules of pyruvate (C₃H₃O₃).
    • Key net reaction:
      extGlucose+2ADP+2NAD++2Pi→2Pyruvate+2ATP+2NADH+2H++2H2Oext{Glucose} + 2\text{ADP} + 2\text{NAD}^+ + 2\text{Pi} \rightarrow 2\text{Pyruvate} + 2\text{ATP} + 2\text{NADH} + 2 H^+ + 2 H_2O

  • Key Steps in Glycolysis:

    • Phosphorylation of glucose, isomerization, and cleavage of fructose 1,6-bisphosphate via aldolase.
    • High-energy phosphoryl transfer leading to ATP production through substrate level phosphorylation.
Further Metabolism of Pyruvate
  • Aerobic Conditions:
    • Pyruvate is oxidized to Acetyl CoA, entering the citric acid cycle.
  • Anaerobic Conditions:
    • Ethanol Fermentation:
    • Pyruvate converted to ethanol:
      extGlucose+2ADP+2Pi→2Ethanol+2ATP+2CO<em>2+2H</em>2Oext{Glucose} + 2\text{ADP} + 2\text{Pi} \rightarrow 2\text{Ethanol} + 2\text{ATP} + 2\text{CO}<em>2 + 2 H</em>2O
    • Lactate Fermentation:
    • Pyruvate converted into lactate:
      Pyruvate→Lactate+NAD+\text{Pyruvate} \rightarrow \text{Lactate} + NAD^+