Topic12.pdf - Topic 12 Acetyl-CoA part 2 Lipid metabolism Readings pp.430 433 442-443 By the end of this topic you should be able to • Identify the

Topic12.pdf - Topic 12 Acetyl-CoA part 2 Lipid metabolism...

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Topic 12 Acetyl-CoA part 2: Lipid metabolism Readings: pp.430, 433, 442-443 Carbohydrates are not the only source of acetyl-CoA for the citric acid cycle. Fatty acids from stored triacylglycerol or from the diet can be degraded and oxidized to acetyl-CoA. When energy is needed from fat storage, lipases in adipocytes degrade triacylglycerol into glycerol and three fatty acids. The released fatty acids enter the bloodstream and are used as fuel in other cells, such as skeletal muscle, heart, and liver. The released glycerol is a substrate for gluconeogenesis. β -oxidation of fatty acids In a cell that is using fatty acids for fuel, specific transporters move fatty acid from the blood into the cytosol. Then, the fatty acid is activated with CoA in the cytosol in a reaction that is driven by hydrolysis of ATP to AMP and PP i . The resulting acyl-CoA is transported into the mitochondrial matrix. There, the acyl-CoA is oxidized in a series of four chemical reactions (Fig 13-11, p.431). Each set of reactions removes two carbons from the fatty acid chain as acetyl-CoA, producing one FADH 2 , one NADH, and a fatty acyl-CoA chain that is two carbons shorter than the starting material. The series repeats, progressively shortening the fatty acid chain until it is entirely oxidized to acetyl-CoA. The net β -oxidation reaction for palmitoyl-CoA (CoA-activated C16:0) from acetyl-CoA present in the matrix is: Palmitoyl-CoA + 7 FAD + 7 NAD + + 7 CoA 8 Acetyl-CoA + 7 FADH 2 + 7 NADH For simplicity, water and protons have been omitted from this equation. An acyl-CoA with 2N carbons produces N acetyl-CoA molecules, N-1 FADH 2 , and N-1 NADH. Because these reactions occur in the matrix, the acetyl-CoA and NADH
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  • Spring '12
  • Deroo
  • Notes, biochem

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