Fatty acid synthesis

Fatty acids are formed by the action of Fatty acid synthases from acetyl-CoA and malonyl-CoA precursors. In humans fatty acids are predominantly formed in the liver and adipose tissue, and mammary glands during lactation. Most acetyl-CoA is formed from pyruvate by pyruvate dehydrogenase in the mitochondria, which is then converted to citrate and is transported into cytosol in the form of citrate.

Elongation

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Much like β-oxidation, elongation occurs via four recurring reactions shown below. In these diagrams, the acetyl and malonyl units are shown as their Acyl carrier protein thioesters: this is how fatty acids are synthesized in microorganisms and plants. However, in animals these same reactions occur on a large dimeric protein, Fatty acid synthase, which has the full complement of enzymatic activities required to synthesize and liberate a free fatty acid.

In the second step of elongation, butyryl ACP condenses with malonyl ACP to form an acyl ACP compound. This continues until a C₁₆ acyl compound is formed, at which point it is hydrolyzed by a thioesterase into palmitate and ACP.