Food Chemistry and Fish in Nutrition

4.3.2.Synthesis of fatty acid

(i) Synthesis of fatty acid

There are three types of fatty acid synthesis. (a) Elongation of existing short chain fatty acid in the mitochondria (b) Microsomal system of chain elongation and (c) The cytoplasmic synthesis of fatty acid from acetyl CoA.

a. Elongation of smaller fatty acid mitochondrial System

Mitochondria catalyses the incorporation of acetyl CoA into smaller chain fatty acids into longer chain fatty acids under anaerobic conditions.

           The enzymes are mostly the same as those involved in β-oxidation except the α - β unsaturated acyl CoA reductase which converts α-β unsaturated acyl CoA to a saturated compound requiring NADPH+H⁺. Thiolase is not used in this pathway. Pyidoxal phosphate is required for the enzyme condensing acetyl CoA with acyl CoA.

b. Microsomal System of elongation of smaller fatty acid

This is the main pathway for the elongation of existing fatty acid molecules. Elongation of fatty acid chains occurs in the endoplasmic reticulum. This pathway the (“microsomal system”) converts fatty acyl-CoA to higher fatty acids using malonyl CoA as acetyl donor and NADPH+H⁺as reducing agent catalyzed by the microsomal fatty acid elongase system of enzymes.

The acyl groups that may act as a primer molecule include the saturated series from C_10-C₁₆ upward, as well as unsaturated C₁₈fatty acids.

Elongation of stearyl-CoA in brain increases rapidly during myelination in order to provide C22 and C24 fatty acids that are needed for the synthesis of sphingolipids.