Metabolism of lipids: Beta oxidation, Biosynthesis of fatty acids.

1. Beta Oxidation (Fatty Acid Degradation)

• Location: Mitochondrial matrix
• Purpose: Breaks down fatty acids to generate acetyl-CoA, NADH, and FADH?.
• Steps of β-Oxidation (Per Cycle):
  1. Activation: Fatty acid + CoA → Fatty acyl-CoA (via acyl-CoA synthetase)
  2. Oxidation: FAD-dependent dehydrogenation → FADH? produced
  3. Hydration: Addition of H?O to form hydroxyacyl-CoA
  4. Oxidation: NAD?-dependent dehydrogenation → NADH produced
  5. Cleavage: Thiolysis releases acetyl-CoA (enters TCA cycle)
• Yield (Per Palmitic Acid, C16:0):
  • 7 cycles → 8 Acetyl-CoA, 7 NADH, 7 FADH?
  • Total ATP (~106 ATP per molecule of palmitic acid)

2. Biosynthesis of Fatty Acids

• Location: Cytoplasm (mainly in liver, adipose tissue)
• Purpose: Converts Acetyl-CoA → Fatty Acids (e.g., Palmitic Acid C16:0)
• Key Steps:
  1. Transport of Acetyl-CoA to Cytoplasm
     • Acetyl-CoA (from mitochondria) is transported as citrate (citrate shuttle).
  2. Activation
     • Acetyl-CoA + CO? → Malonyl-CoA (via Acetyl-CoA carboxylase, rate-limiting step).
  3. Fatty Acid Synthase (FAS) Complex
     • Sequential addition of 2-carbon units from malonyl-CoA.
     • Steps: Condensation → Reduction → Dehydration → Reduction
  4. Final Product: Palmitic Acid (C16:0) → Further modified to longer FAs.
• Energy Requirement: 1 ATP per Malonyl-CoA formation, 2 NADPH per cycle.