قناة ثالثة بشري (دفعه 52)

9. Importance of β-Oxidation • Major energy source • Produces acetyl-CoA for: • Citric acid cycle • Ketone body formation • Provides ketone bodies as an energy source for the brain during fasting 10. Oxidation of Odd-Chain Fatty Acids • Undergo β-oxidation until propionyl-CoA (3 carbons) is formed • Propionyl-CoA → Succinyl-CoA • Succinyl-CoA enters the citric acid cycle

6. Steps of β-Oxidation Each cycle shortens the fatty acid chain by two carbons and consists of four reactions: 1. Dehydrogenation • Enzyme: Acyl-CoA dehydrogenase • Produces: FADH₂ (2 ATP) • Forms: trans-enoyl-CoA 2. Hydration • Enzyme: Enoyl-CoA hydratase • Adds water → 3-hydroxyacyl-CoA 3. Dehydrogenation • Enzyme: 3-hydroxyacyl-CoA dehydrogenase • Produces: NADH (3 ATP) • Forms: 3-ketoacyl-CoA 4. Thiolytic Cleavage • Enzyme: Thiolase • Produces: • Acetyl-CoA (12 ATP) • Fatty acyl-CoA shortened by 2 carbons The shortened fatty acyl-CoA re-enters the cycle. 7. General Formula • Number of β-oxidation cycles = (n/2) − 1 • Number of acetyl-CoA molecules = n/2 (where n = number of carbon atoms) 8. Energy Yield from β-Oxidation (Palmitic Acid Example) Palmitoyl-CoA (C16) produces: • 8 Acetyl-CoA • 7 NADH • 7 FADH₂ Total ATP generated = 131 ATP ATP used for activation = 2 ATP Net ATP yield = 129 ATP

4. Transport of Long-Chain Fatty Acids Long-chain fatty acyl-CoA cannot cross the inner mitochondrial membrane (IMM). Carnitine Shuttle System 1. CPT-I (outer mitochondrial membrane): Converts fatty acyl-CoA → acylcarnitine 2. Carnitine–acylcarnitine translocase: Transports acylcarnitine across the IMM 3. CPT-II (inner mitochondrial membrane): Converts acylcarnitine → fatty acyl-CoA in the matrix Carnitine returns to cytosol 🔹 Carnitine is synthesized in the liver from the amino acid lysine. 5. Entry of Short- and Medium-Chain Fatty Acids • Fatty acids with <12 carbons • Can cross the IMM without carnitine • Activated and oxidized directly inside mitochondria

2. β-Oxidation of Fatty Acids β-oxidation is the major pathway for fatty acid catabolism. It is a mitochondrial pathway in which fatty acids are oxidized at the β-carbon, resulting in the sequential removal of two-carbon units as acetyl-CoA. Key Features • Occurs in the mitochondrial matrix • Fatty acids are activated in the cytoplasm • Produces: • Acetyl-CoA • NADH • FADH₂ • Long-chain fatty acids require transport into mitochondria

لوز اللوز شباب هذا الشورت نوت ،، بالله احفظوهن ♥️.