Fatty Acid Biosynthesis
We make fatty acids as well as break them down. Fatty acids are synthesized in the cytosol. The pathway of fatty acid biosynthesis is not just the reverse of fatty acid degradation, although there are some interesting parallels between the two pathways.
Biosynthesis of Palmitic Acid
Two enzymes synthesize palmitate from acetyl CoA.
Acetyl CoA Carboxylase
In this reaction a carboxyl group is added to acetyl CoA to generate malonyl CoA. This biotin-containing enzyme catalyzes the committed step in fatty acid biosynthesis and is subject to a complex regulation not covered in this activity.
Fatty Acid Synthase
This enzyme is one of the most complex in our bodies. It consists of three polypeptide chains, two of which are identical to each other. The third is a very small polypeptide called acyl carrier protein (ACP), which contains a phosphopantetheine group (derived from the vitamin panthothenic acid) that is identical to the one in Coenzyme A. The other two polypeptides have 7 different enzymatic activities. The enzyme works by first mobilizing malonyl CoA and acetyl CoA (attaching them to ACP). Then the enzyme begins a cycle of reactions in which a fatty acid grows from ACP. At the end of each cycle the growing fatty acid is 2 carbons long. When the fatty acid has reached 16 carbons in length, it is cleaved from the ACP.
The activities of fatty acid synthase are as follows:
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