Fatty acids are monocarboxylic acids, which are the main components of simple lipids, complex fats and binding fats. Fatty acids can be obtained when the above lipids are hydrolyzed, so they are classified as derived fats. Similarly, glycerol, acetyl-CoA, etc. are derived lipids.
Fatty acids in animals and plants are relatively simple, they are all straight-chain, and can contain multiple double bonds, while bacterial fatty acids have only one double bond at most. The carbon chain structure of fatty acids of bacteria is more complex, and can contain branched chains or lipid rings, such as tuberculosis acid is saturated branched-chain fatty acids. Plants may contain triple bonds, epoxy groups, and cyclopropylene groups.
The fatty acids in humans and higher animals are straight-chain even carbon monobasic acids, the most common of which are c16, c18, c22 and other long-chain fatty acids. The unsaturated fatty acids in the human body are all cis-double bonds, and fatty acids with multiple double bonds are called highly unsaturated fatty acids or polyunsaturated fatty acids. Methylene is inserted between adjacent double bonds and does not constitute a conjugate system.
Some plant-derived fatty acids contain more conjugate double bonds, which are placed in the air and can form a dry and ductile film on the surface, a phenomenon called drying. The drying performance of tung oil acid from the seeds of tung oil is good, so tung oil can withstand cold, heat and humidity, and is used in ancient times to make oil paper umbrellas, and modern use is waterproof to ships, electrical appliances and so on.
Tung oleic acid
Fatty acids have common names, system names, and abbreviations. The common name mainly reflects its source and characteristics, and the system name reflects its number of carbon atoms, the number of double bonds and its location. For example, the system name of stearic acid is octadecanic acid, represented by 18:0, where "18" indicates the length of the carbon chain and "0" indicates a double bond; oleic acid is octadecaenoic acid, represented by 18:1, and "1" indicates that there is a double bond. Anti-oleic acid is represented by 18:1Δ9, trans.
There are two ways to represent the position of the double key, namely the Δ numbering system and the ω (or n) numbering system. The former locates the double bond by the systematic ordinal of the carbon atom (starting from the number of carboxyl terminals) of the carbon atom on the carboxyl side of the double bond. The latter uses the reciprocal ordinal of the carbon atom (starting from the methyl terminal) and locates the double bond with the (reciprocal) ordinal of the carbon atom on the side of the double bond.
Two two-key positioning methods
The advantage of reciprocal ordinal numbers is that fatty acids can be divided into 4 metabolically related groups, namely omega3, omega6, omega7, and omega9. In mammals, fatty acids can only be derived from this group of mothers, which are soft oleic acid (16:1, omega 7), oleic acid (18:1, omega 9), linoleic acid (18:2, omega 6) and α linolenic acid (18:3, omega 3).
Mammals can synthesize saturated fatty acids and monounsaturated fatty acids, and cannot synthesize polyunsaturated fatty acids, such as linoleic acid, linolenic acid and the like. Fatty acids that are necessary to maintain the normal growth of mammals and cannot be synthesized in the body are called essential fatty acids. Strictly speaking, the really essential fatty acids are linoleic acid and linolenic acid, two mothers, and the others can be synthesized on this basis.
Fatty acids can be divided into four groups according to the length of the carbon chain:
Short-chain fatty acids (scfa): carbon atom number 1-5;
Medium chain fatty acids (mcfa): carbon atom number 6-12;
Long-chain fatty acids (lcfa): carbon atom number 13-21;
Very long chain fatty acids (vlcfa): the number of carbon atoms is more than 21.
Short-chain fatty acids can cross the blood-brain barrier through monocarboxylic acid transporters. Dietary fiber fermentation in the colon produces short-chain fatty acids, mainly acetic, propionic and butyric acid. Butyric acid is the most important because it is the main source of energy for colonic epithelial cells.
butyric acid
Medium-chain fatty acid triglycerides (MCTs) can spread from the gastrointestinal tract to the portal venous system, thereby being rapidly absorbed by the body, so it can be used to treat various malabsorption diseases. MCTs are easily metabolized, induce ketogenicity, and can be used as a ketogenic diet for epilepsy treatment. However, it is necessary to prevent metabolic acidosis.
Long-chain fatty acid triglycerides need to be digested into fatty acids to be absorbed, which are then re-esterified to form chylomicrons, which enter the bloodstream through the lymphatic system.
Very long chain fatty acids are found in the brain, retina, etc., and are used to synthesize ceramides and form various membrane structures. Its biosynthesis is carried out in the endoplasmic reticulum, while metabolism is carried out in the peroxisomes, because it cannot enter the mitochondrium.
Docosahexaenoic acid (dha)