Fatty Acids

Figure 1. Three-dimensional representations of several fatty acids. Saturated fatty acids have perfectly straight chain structure. Unsaturated ones are typically bent, unless they have a trans configuration.

In biochemistry, a Fatty Acid is a carboxylic acid with an aliphatic (or hydrocarbon) chain which can be either saturated or unsaturated (i.e. whether their molecular structure contains a carbon double bond or not). Saturated Fatty Acids do not have any carbon double bonds; whereas unsaturated Fatty Acids have at least one carbon double bond or more.

Examples of saturated Fatty Acids:

• Caprylic acid
• Capric acid
• Lauric acid
• Myristic acid
• Palmitic acid
• Stearic acid
• Arachidic acid
• Behenic acid
• Lignoceric acid
• Cerotic acid

Examples of unsaturated Fatty Acids:

• Myristoleic acid
• Palmitoleic acid
• Sapienic acid
• Oleic acid
• Elaidic acid
• Vaccenic acid
• Linoleic acid
• Linoelaidic acid
• alpha-Linolenic acid
• Arachidonic acid
• Eicosapentaenoic acid (EPA)
• Erucic acid
• Docosahexaenoic acid (DHA)

Aside from being saturated or unsaturated, Fatty Acids can also be classified according to their molecular length.

• Short-chain fatty acids (SCFA) are fatty acids with aliphatic tails of five or fewer carbon atoms.
• Medium-chain fatty acids (MCFA) are fatty acids with aliphatic tails of 6 to 12 carbon atoms, which can form medium-chain triglycerides.
• Long-chain fatty acids (LCFA) are fatty acids with aliphatic tails of 13 to 21 carbon atoms.
• Very long chain fatty acids (VLCFA) are fatty acids with aliphatic tails of 22 or more carbon atoms.

Fatty Acids are both important dietary sources of fuel for animals and important structural components for cells. In animals, Fatty Acids are formed from carbohydrates predominantly in the liver, adipose tissue, and the mammary glands during lactation.

Fatty Acids are insoluble in water. They can only be broken down in mitochondria (i.e. the "power generator" within cells) via beta oxidation and subsequently, reactions with oxygen, which generates a lot of energy for cells (ATP). However, cells in the central nervous system cannot absorb free Fatty Acids from blood, as the blood-brain barrier is impervious to most free Fatty Acids. Cells in the central nervous system have to manufacture their own Fatty Acids from carbohydrates in order to produce and maintain the phospholipids of their cell membranes and those of their organelles.

Essential Fatty Acids are Fatty Acids that are required for good health but cannot be made in sufficient quantity within the human body. Two essential Fatty Acids in the human body are Linoleic Acid and alpha-Linoleic Acid (ALA). These Fatty Acids are widely provided by plant oils. The human body has limited ability to convert ALA into Eicosapentaenoic acid (EPA) and Docosahexaenoic acid (DHA), which form the primary structural component of the human brain, cerebral cortex, skin, and retina. Essential Fatty Acids must be supplemented through dietary intake.