All of the following statements about fatty acid synthesis are true, except:
Palmitoleic acid is not the end product of fatty acid synthesis. The end product of Fatty acid Synthesis is palmitic acid which is a saturated fatty acid conataining 16 carbons (Free palmitate-C-16). This is the primary form in which fats are stored as triacylglycerol. Palmitoleic acid is a monounsaturated fatty acid synthesized by the desaturation of palmitic acid. Fatty acid synthesis: Lipogenesis The main pathway for denovo synthesis of fatty acids (lipogenesis) occurs in the cytosol. Fatty acids are synthesized by an extra-mitochondrial system. The pathway conves acetyl-CoA to palmitate. Acetyl-CoA is the immediate substrate and free palmitic acid or palmitate is the end product. Citrate shuttle is required for the pathway. The first step in de novo fatty acid synthesis is the transfer of acetate units from mitochondrial acetyl CoA to the cytosol. The CoA poion of acetyl CoA cannot cross the inner mitochondrial membrane. For fatty acid biosynthesis , acetyl-CoA has to be transpoed from the mitochondria to the cytoplasm. This is done a shuttle system called the Citrate Shuttle. Its cofactor requirements include NADPH, ATP, Mn2+, biotin, Pantothenic acid and HCO3- (as a source of CO2) The synthesis of long-chain fatty acids (lipogenesis) is carried out by two enzyme systems. Acetyl-CoA carboxylase and Fatty acid synthase. Acetyl-Co-A carboxylase Fatty acid synthase Acetyl-Co-A carboxylase conves acetyl-CoA to malonyl-CoA. This is an irreversible reaction. This is an rate limiting step for fatty acid synthesis Lipogenesis is regulated at the acetyl-CoA carboxylase step by allosteric modifiers and Phosphorylation/de-phosphorylation The enzyme is allosterically activated by citrate and deactivated by long-chain acyl-CoA. Dephosphorylation (eg., by insulin) promotes the enzyme activity phosphorylation (eg., by glucagon or epinephrine) inhibits enzyme activity Fatty acid synthase, catalyzes the formation of palmitate from one acetyl-CoA and seven malonyl-CoA molecules Fatty acid synthase is not a single enzyme but a multienzyme complex consisting of two identical polypeptide chains, each containing six separate enzymatic activities and Acyl Carrier Proteins (ACP) NADPH is the reducing agent during fatty acid synthesis. Ref: Harper
Occurs in cytosol
Citrate shuttle is required
Acetyl CoA is the immediate substrate
Palmitoleic acid is the end product
Metabolism of lipid