lipid biosynthesis - wou homepage - western …guralnl/451lipid biosynthesisi.pdf · lipid...
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Lipid Biosynthesis
• Fatty acid synthesis• Saturated fatty acids• Regulation• Elongation• Unsaturation
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Fatty acid nomenclature
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Comparison of synthesis and degradation
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Fatty Acid Synthesis
• Occurs mainly in liver and adipocytes (mammals)
• FA synthesis and degradation occur by two completely separate pathways
• When glucose is plentiful, large amounts of acetyl CoA are produced by glycolysis and can be used for fatty acid synthesis
• Glucose oxidation in the pentose phosphate pathway provides NADPH for FA synthesis
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Transfer of Acetyl CoA
• Acetyl CoA from catabolism of carbohydrates and amino acids is exported from mitochondria via the citrate transport system (Fig 16.15, next slide)
• Cytosolic NADH also converted to NADPH• Two molecules of ATP are expended for each round of this cyclic pathway • One molecule of NADPH is produced for each acetyl CoA• Transferred from the mitochondria. Produce 8 NADPH for one Palmitate
produced.
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Formation of Malonyl CoA• Acetyl Co A carboxylase• Biotin containing enzyme• Carboxybiotin intermediate is formed• Hydrolysis of ATP catalyzes the reaction• Regulatory site for Fatty acid biosynthesis
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Intermediates attached to Acylcarrier protein
• Phosphopantetheine group in ACP and coenzyme A
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Biosynthesis of Fatty acid
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Detailed Reactions
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Condensation stage
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Final reaction of FA synthesis
• Rounds of synthesis continue until a C16 palmitoyl group is formed
• Palmitoyl-ACP is hydrolyzed by a thiolesterase
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Overall stoichiometry of palmitate synthesis from acetyl CoA and malonyl CoA
Acetyl CoA + 7 Malonyl CoA + 14 NADPH + 14 H+
Palmitate + 7 CO2 + 14 NADP+ + 8 HS-CoA + 6 H2O
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FA synthase complex