There is recent evidence that lipids are also important as signaling molecules within the body, sometimes serving as a marker for programmed cell death. Essay 2. A current designation is based on the position of the end most double bond, counting from the methyl CH3 carbon, called the omega end.
The most important omega fatty acids are: Omega 6 — linolein and arachidonic acids and Omega 3 — linolenic, icosapentaenoic, and docosahexaenoic acids. They are the esters of three molecules of fatty acids plus one molecule of glycerol; the fatty acid may be all different. As they include three fatty acids, fats and oils are also known as triglycerides. They are found in adipose tissue, butterfat, lard, suet, fish oils, olive oil, corn oil, etc. Some fats are saturated, while others are unsaturated.
These terms refer to the presence or absence of double bonds in the fatty acids of fats. Saturated fats have no double bonds, whereas unsaturated fats contain one or more such bonds.
In general, plant fats are unsaturated and animal fats are saturated. Saturated fats are generally solid at room temperature, while unsaturated fats are typically liquid. Like all fats, the hydrocarbon tails of phospholipids do not dissolve in water.
However, phosphate groups are polar and soluble in water. The different solubilities of the two ends of phospholipid molecules allow them to form the bilayers that make up the cell membrane Fig. This lipoprotein coating is called myelin sheath. On digestive tract they facilitate the digestive process depressing gastric secretion, slowing gastric emptying and stimulating biliary and pancreatic flow. Bile salts by-products of cholesterol are natural detergents synthesized in the liver and secreted into bile.
They solubilize phospholipids and cholesterol in the bile, permitting the secretion of cholesterol into the intestine the excretion of both cholesterol and bile salts is the major way by which cholesterol is removed from the body. Bile salts also aid in the digestion and absorption of fat and soluble-fat vitamins in gut.
In many animals, some lipids are secreted into external environment and act as pheromones that attract or repel other organisms. They affect the texture and flavor of food and so its palatability.
Food manufacturers use fat for its textural properties, e. The mixture molecules show combined characteristics and perform special functions. E ssay 4. Classification s of Lipids: Based on chemical composition lipids are classified as follows: 1.
Simple lipids or Homolipids: These are esters of fatty acids with various alcohols. A fat is solid at ordinary room temperature whereas oil is liquid. Compound lipids or Heteroliplds: These are esters of fatty acids with alcohol and having additional group s.
Derived lipids: These are the substances derived from simple and compound lipids by hydrolysis. These include fatty acids, alcohols, mono- and diglycerides, steroids, terpenes and carotenoids. They are the major components of storage or depot fats in plant and animal cells but are not normally found in membranes.
Most fats and oils, upon hydrolysis, yield several fatty acids as well as glycerol. Their generic formula is shown in the following figure: Obviously, when the groups attached to carbon 1 and 3 differ, a centre of asymmetry is created at C A fat molecule contains 3 moles of fatty acids, which may be similar or dissimilar.
Most of the triglycerides in nature are mixed or asymmetrical triglycerides, i. Most animal fats such as those from meat, milk and eggs are relatively rich in saturated fatty acids but contain a rather low content of polyunsaturated fatty acids Table—3. The large proportion of saturated fatty acids esp. The plant fats, on the other hand, contain a large proportion of polyunsaturated fatty acids.
The unsaturated fatty acids have low melting point and gives liquid state to the plant fats in normal temperature. These are esters of long- chain saturated and unsaturated fatty acids with long-chain monohydroxy alcohols other than glycerol. The fatty acids range in between C14 and C36 and the alcohols range from C16 to C These alcohols may be aliphatic or alicyclic.
Cetyl alcohol is most commonly found in waxes. The leaves of many plants such as Rhododendron, Calotropis, etc. Waxes also serve as the chief storage form of fuel in planktons.
Water is the biological milieu—the substance that makes life possible—and almost all the molecular components of living cells, whether they be found in animals, plants, or microorganisms, are soluble in water. Therefore a balance of lipids is crucial to health. Eicosanoids play important roles affecting inflammation, immunity, mood, and behavior. Although biological lipids are not large macromolecular polymers e.
A prostaglandin can have opposite effects, depending on which receptor it binds to. A number of diseases are related to lipids in the human body.
They structurally resemble lecithins and cephalins but have one of the fatty acids replaced by an unsaturated ether. Movement The movement of fats in the body is important because they are not stored in all cells. Functions of Lipids 3. Terpenes have a variety of functions.
The bound complexes are then internalized by endocytosis, degraded in the lysosomes, and the cholesterol is disbursed in liver cells. See Article History Alternative Title: oil Lipid, any of a diverse group of organic compounds including fats, oils, hormones, and certain components of membranes that are grouped together because they do not interact appreciably with water. Vitamin C is one such donor. Another substance that is found in the membrane is glycolipids, these are complexes of lipid and polysaccharides.