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The word lipid indicates a wide range of compounds.

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Lipids The word lipid indicates a wide range of compounds.These may conveniently be divided into two groups - the first consists of fats and oils, the second includes steroids and terpenes together with fat-soluble vitamins and some other compounds. Fats, oils and phospholipids are the most common lipids in living cells. Lipids contain elements C, H and O with the ratio of H : O is greater than 2:1, example: C6H38O6. Lipids are denser than carbohydrates (because of these extra H atoms) and therefore contain more chemical potential energy, than carbohydrates. A gram of lipid yields more kinetic energy (38 Kj) when oxidised than a gram of carbohydrate (17Kj). Lipids are made up of two parts: * Glycerol. * Fatty acids. Lipids are formed by dehydration synthesis of glycerol (alcohol) and 3 fatty acids. Lipids also contain small amounts of other elements, such as phosphorus. ...read more.


In other words, there are no carbon - to - carbon double bonds. Fats which are solid at room temperature contain saturated fatty acids. E.g butter or lard Unsaturated fatty acids(in unsaturated fats) Example: Oloeic acid. The presence of double bonds - allow more hydrogen atoms to be added to it. Formation of lipids A triglyceride forms by the condensation of one glycerol and three fatty acids in the presence of lipase. A Hydrogen ion is removed from the glycerol molecule and an OH- group from the fatty acid. These unite to form water. Ester bonds are formed. Note that this is a reversible reaction by hydrolysis, when a lipid is hydrolysed into one glycerol and three fatty acids. Physical properties of lipids * Lipids are insoluble in water, due to their long hydrocarbon chains, but in organic solvents such as ether, benzene and chloroform they will dissolve. ...read more.


In whales and seals this is known as blubber. * Phospholipids play an important role in the structure of the plasma membranes. * Lipids may act as a source of metabolic water. When respired they yield water and carbon dioxide. Some desert animals are so efficient in their conservation of water that they obtain their water from the foods they eat or from the metabolism of fat (camels). * Fats form waxes which waterproofs the cuticles of plants and the integuments of animals, and cerumen in mammalian ears (ear wax) which has a protective function. * Fats and oils are insoluble in water, and are therefore osmotically inactive. This makes them a useful storage form. In plants fat is stored in seeds, for example: peanuts. * Protect against mechanical injury, for example: fat around internal animal organs such as the heart and kidneys. * Fats are important for the absorption of fat-soluble vitamins A,D,E and K by mammals. * Lipids occur in the Myelin sheath of nerves as an insulating layer around nerve fibres. ...read more.

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