FATTY ACID SYNTHESIS

FATTY ACID SYNTHESIS
A large proportion of the fatty acids used by the body is supplied by the diet. Occurs mainly in liver adipocytes, in mammary glands during lactation Occurs in cytoplasm .When glucose is plentiful, large amounts of acetyl CoA are produced by glycolysis and can be used for fatty acid synthesis .
In fatty acid synthesis occurs primarily in the liver and adipose tissue, the process incorporates carbons from acetyl CoA into the growing fatty acid chain, using ATP and reduced nicotinamide adenine dinucleotide phosphate (NADPH).
Three stages of fatty acid synthesis:
A. Production of cytosolic acetyl CoA and NADPH

The first step in fatty acid synthesis is the transfer of acetate units from mitochondrial acetyl CoA to the cytosol. Mitochondrial acetyl CoA is produced by the oxidation of pyruvate. The coenzyme A portion of acetyl CoA, however, cannot cross the mitochondrial membrane; only the acetyl portion is transported to the cytosol. It does so in the form of citrate produced by the condensation of oxaloacetate (OAA) and acetyl CoA
This process of translocation of citrate from the mitochondrion to the cytosol, where it is cleaved by ATP-citrate lyase to produce cytosolic acetyl CoA and OAA, occurs when the mitochondrial citrate concentration is high. Therefore, cytosolic citrate may be viewed as a high-energy signal. Because a large amount of ATP is needed for fatty acid synthesis, the increase in both ATP and citrate enhances this pathway.