Syntheses of fat acids

Formation of fatty acids. Fatty acids are synthesized in various tissues, especially in the liver and adipose tissue. The starting point for fatty acid synthesis is acetyl-CoA.

Biological fatty acid synthesis proceeds in the same way as degradation through the gradual addition of acetyl-CoA (activated acetic acid) CH3CO-CoA. This also explains why the fatty acid molecules usually have an even number of carbon atoms.

In contrast to the breakdown of fatty acids, beta-oxidation, which takes place in the mitochondrial matrix (glycolysis) and is carried out by pyruvate dehydrogenase (PDH), the synthesis of fatty acids takes place in the cytosol. Thus, synthesis and degradation of fatty acids take place in different compartments. Fatty acid synthesis exclusively supplies saturated fatty acids. Their most important product is palmitic acid (16 carbon atoms). Shorter fatty acids are synthesized by the fatty acid synthase only to a lesser extent. Longer fatty acids are not synthesized by fatty acid synthase.

Unsaturated fatty acids are formed by insertion of double formations in the endoplasmic reticulum and are catalyzed by the desaturases. The transfer of the required electrons to the enzyme is mediated by cytochrome b5. Desaturases can only introduce double bonds between the first 10 atoms of the fatty acids. In this respect, linoleic acid and linolenic acid must be ingested with food as essential fatty acids.

Chain extension (elongation) is possible both in the mitochondria and in the endoplasmic reticulum independently of each other.