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Fatty acid synthesis starts with acetyl-CoA and builds up by the addition of two-carbon units. Fatty acid synthesis occurs in the cytoplasm of cells while oxidative degradation occurs in the mitochondria. Many of the enzymes for the fatty acid synthesis are organized into a multienzyme complex called fatty acid synthase. [5]
Fatty acids exhibit reactions like other carboxylic acids, i.e. they undergo esterification and acid-base reactions. Fatty acids do not show a great variation in their acidities, as indicated by their respective pK a. Nonanoic acid, for example, has a pK a of 4.96, being only slightly weaker than acetic acid (4.76).
Synthesis of saturated fatty acids via fatty acid synthase II in E. coli. Straight-chain fatty acid synthesis occurs via the six recurring reactions shown below, until the 16-carbon palmitic acid is produced. [2] [3] The diagrams presented show how fatty acids are synthesized in microorganisms and list the enzymes found in Escherichia coli. [2]
Hexanoic acid CH 3 (CH 2) 4 COOH C6:0 Enanthic acid: Heptanoic acid CH 3 (CH 2) 5 COOH C7:0 Caprylic acid: Octanoic acid CH 3 (CH 2) 6 COOH C8:0 Pelargonic acid: Nonanoic acid CH 3 (CH 2) 7 COOH C9:0 Capric acid: Decanoic acid CH 3 (CH 2) 8 COOH C10:0 Undecylic acid: Undecanoic acid CH 3 (CH 2) 9 COOH C11:0 Lauric acid: Dodecanoic acid CH 3 (CH ...
Long chain fatty acids (more than 14 carbon) need to be converted to fatty acyl-CoA in order to pass across the mitochondria membrane. [6] Fatty acid catabolism begins in the cytoplasm of cells as acyl-CoA synthetase uses the energy from cleavage of an ATP to catalyze the addition of coenzyme A to the fatty acid. [6]
[2]: 634 Fatty acids are made by fatty acid synthases that polymerize and then reduce acetyl-CoA units. The acyl chains in the fatty acids are extended by a cycle of reactions that add the acetyl group, reduce it to an alcohol, dehydrate it to an alkene group and then reduce it again to an alkane group.
Lipids (oleaginous) are chiefly fatty acid esters, and are the basic building blocks of biological membranes. Another biological role is energy storage (e.g., triglycerides ). Most lipids consist of a polar or hydrophilic head (typically glycerol) and one to three non polar or hydrophobic fatty acid tails, and therefore they are amphiphilic .
The fatty acids in phospho- and glycolipids usually contain an even number, typically between 14 and 24, of carbon atoms, with 16- and 18-carbon being the most common. FAs may be saturated or unsaturated, with the configuration of the double bonds nearly always cis .