In biochemistry, fatty acids are defined as carboxylic acids with long aliphatic chains that may be branched or branched. Naturally occurring fatty acids contain an even number of carbon atoms and are usually unbranched. Fatty acids are the main components of lipids; They exist in three main forms of esters: phospholipids, triglycerides, and cholesterol esters.
Types of fatty acids
Fatty acids are classified based on the number, length, and concentration of their carbons.
Even and odd chain fatty acids
Most naturally occurring fatty acids have an even number of carbons in their aliphatic chain. Example: oleic acid (18), stearic acid (18). However, some fatty acids have an odd number of carbons in their chain. They are called odd chain fatty acids (OCFA). Example: heptadecanoic and pentadecanoic acid found in dairy products.
The biosynthesis of odd chain fatty acids is slightly more complex than that of even chain fatty acids.
Saturated and unsaturated fatty acids
Acids that do not have a double bond (C=C) in the aliphatic chain are called saturated fatty acids. The chemical formula of saturated fatty acids can be written as CH 3 (CH 2 ) n COOH. Below are the common saturated fatty acids.Caprylic acid, capric acid, lauric acid, myristic acid, palmitic acid, stearic acid. Unsaturated fatty acids contain at least one double bond in their aliphatic chain. The double bond in the molecule gives rise to two isomers for unsaturated fatty acids: cis and trans structures.
In cis isomers two hydrogen atoms are placed near the double bond on the same side of the aliphatic chain. The double bond gives rigidity to the molecule and the cis conformation limits the conformational freedom of the fatty acid. The greater the number of cis bonds found in a fatty acid, the less flexible and bent the conformation becomes. Example: oleic and linoleic acid.
Trans isomers, in contrast, have two hydrogen atoms placed on opposite sides of the aliphatic chain. The trans configuration does not bend the structure of the molecule as seen in the cis isomers, but remains straight as in saturated fatty acids. Most naturally occurring unsaturated fatty acids have the cis structure, but most trans fats are the result of human processing and do not occur naturally.
Length of fatty acids
Fatty acids with aliphatic chains of five or fewer carbons are called short-chain fatty acids (SCFA). Example: Butyric acid Fatty acids with aliphatic chains of 6 to 12 carbons are called medium chain fatty acids (MCFA). Example: Capric acid.
Fatty acids with aliphatic chains of 13 to 21 carbons are called long-chain fatty acids (LCFA). Example: Oleic acid. Fatty acids with aliphatic chains of 22 or more carbons are called very long chain fatty acids (VLCFA). Example: Lignoceric acid.
Properties of fatty acids
Acidity: Fatty acids have similar acidity. As the chain length of a fatty acid increases, their solubility in water decreases, which has no effect on the pH of the aqueous solution. Example: Nonanoic acid (C9) has a pK a of 4.96 and acetic acid (C2) has a pK a of 4.76.
Hydrogenation: Unsaturated fatty acids are prone to dehydrogenation (oxidation or hydrolysis of the fat when exposed to air). So to reduce this problem unsaturated fatty acids undergo hydrogenation.
Auto-oxidation: Unsaturated fatty acids undergo a chemical change in the presence of air and trace metals. Treatment with chelating agents can inhibit this process by removing metal catalysts.
Ozonolysis: Unsaturated fatty acids are more prone to degradation by ozone.
Fatty acid cycle
Digestion and Intake: SCFA and MCFA are absorbed directly into our blood by the intestinal capillaries and travel through the hepatic portal vein just like other absorbed nutrients. However, LCFA are not directly absorbed into the blood. They are absorbed in the villi of the intestine and form triglycerides. Triglycerides are coated with cholesterol and proteins to form chylomicrons.
Chylomicrons are transported by lymphatics to a site near the heart, where they are stored or broken down for energy.
Metabolism: Fatty acids are broken down into CO 2 and water in the mitochondria by beta-oxidation and the citric acid cycle. After oxidative phosphorylation they release energy in the form of ATP.