CH24 - Chapter 24 Lipid Biosynthesis Chapter 24 Lipid Biosynthesis ChapterOutline : (ACP: serine:CoA

CH24 - Chapter 24 Lipid Biosynthesis Chapter 24 Lipid...

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Chapter 24 · Lipid Biosynthesis Chapter 24 Lipid Biosynthesis . . . . . . . . . . . . . . . . . . . . . . . . Chapter Outline Fatty acid biosynthesis Biosynthesis localized in cytosol: Fatty acid degradation in mitochondria Intermediates held on acyl carrier protein (ACP): Phosphopantetheine group attached to  serine: CoA in degradation Fatty acid synthase: Multienzyme complex Carbons derived from acetyl units Acetyl CoA to malonyl CoA by carboxylation Acetyl unit added to fatty acid with decarboxylation of malonyl CoA Carbonyl carbons of acetyl units reduced using NADPH Source of acetyl units Amino acids, glucose Acetyl CoA used to produce citrate Citrate exported to cytosol: ATP-citrate lyase forms acetyl-CoA and oxaloacetate Source of NADPH Oxaloacetate utilization Oxaloacetate (from citrate) to malate: NADH dependent reaction Malate to pyruvate: Malic enzyme: NADPH produced Pentose phosphate pathway Malonyl-CoA production: Acetyl-CoA carboxylase Biotin-dependent enzyme ATP drives carboxylation Enzyme regulation Filamentous polymeric form active Citrate favors active polymer Palmitoyl-CoA favors inactive protomer (polymer’s monomer or  building block molecule) Citrate/palmitoyl-CoA effects depend on state of phosphorylation of  protein o Unphosphorylated protein binds citrate with high affinity:  Activation o Phosphorylated protein binds palmitoyl with high affinity:  Inactivation Acetyl transacetylase: Acetylates acyl carrier protein (ACP): Destined to become methyl end of  fatty acid Malonyl transacetylase: Malonylates ACP -Ketoacyl-ACP synthase (acyl-malonyl ACP condensing enzyme): Accepts acetyl group:  Transfers acyl group to malonyl-ACP Malonyl carboxyl group released: Decarboxylation drives synthesis 128
Chapter 24 · Lipid Biosynthesis Malonyl-ACP converted to acetoacetyl-ACP -Ketoacyl-ACP reductase Carbonyl carbon reduced to alcohol NADPH provides electrons -Hydroxyacyl-ACP dehydratase: Elements of water removed: Double bond created 2,3-trans-Enoyl-ACP reductase Double bond reduced NADPH provides electrons Subsequent cycles: C-16: Palmitoyl-CoA Additional modifications Elongation Mitochondrial-based system uses reversal of  -oxidation Endoplasmic reticulum-based system uses malonyl-CoA Monounsaturation: One double bond Bacteria: Oxygen-independent pathway: Chemistry performed on carbonyl  carbon Eukaryotes: Oxygen-dependent pathway Polyunsaturation Plants can add double bonds between C-9 and methyl end Animals Add double bonds between C-9 and carboxyl end Require essential fatty acids to have double bonds closer to methyl end Regulation Malonyl-CoA inhibition of carnitine-acyl transferase: Blocks fatty acid uptake Citrate/palmitoyl regulation of acetyl-CoA carboxylase Complex lipids Glycerolipids: Glycerol backbone Glycerophospholipids Triacylglycerols Sphingolipids: Sphingosine backbone Phospholipids Sphingolipids Glycerophospholipids Glycerolipid biosynthesis

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