Fatty acids are synthesized by the condensation of two-carbon units. Furthermore, in terms of the enzymic steps contained, the procedure is not the reverse of β- oxidation. Fatty acid synthesis contained a separate series of reactions to build up long-chain hydrocarbons from acetyl CoA units. The key differences between fatty acid synthesis and breakdown are:
a) Whereas their degradation occurs in the mitochondria of eukaryotes, fatty acid synthesis happens in the cytosol of both eukaryotes or prokaryotes;
b) Whereas NADH is produced in β-oxidation, fatty acid synthesis uses NADPH as the reductant ;
c) During their synthesis, fatty acids are covalently attaches to an ACP (acyl carrier protein) as opposed to CoA in their degradation;
d) Whereas in β-oxidation the individual activities are present on separate enzymes the enzyme activities of fatty acid synthesis in higher organisms are present in a single, multifunctional polypeptide chain (as a dimer) called as fatty acid synthase, .