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In 1815, Henri Braconnot classified lipids ( graisses) in two categories, suifs (solid greases or tallow) and huiles (fluid oils). Lipid may be regarded as organic substances relatively insoluble in water, soluble in organic solvents(alcohol, ether etc.) actually or potentially related to fatty acid and utilized by the living cells. Although humans and other mammals use various biosynthetic pathways both to break down and to synthesize lipids, some essential lipids can't be made this way and must be obtained from the diet. Lipids also encompass molecules such as fatty acids and their derivatives (including tri-, di-, monoglycerides, and phospholipids), as well as other sterol-containing metabolites such as cholesterol. Īlthough the term "lipid" is sometimes used as a synonym for fats, fats are a subgroup of lipids called triglycerides. Using this approach, lipids may be divided into eight categories: fatty acids, glycerolipids, glycerophospholipids, sphingolipids, saccharolipids, and polyketides (derived from condensation of ketoacyl subunits) and sterol lipids and prenol lipids (derived from condensation of isoprene subunits). Biological lipids originate entirely or in part from two distinct types of biochemical subunits or "building-blocks": ketoacyl and isoprene groups. Scientists sometimes define lipids as hydrophobic or amphiphilic small molecules the amphiphilic nature of some lipids allows them to form structures such as vesicles, multilamellar/ unilamellar liposomes, or membranes in an aqueous environment. Lipids have applications in the cosmetic and food industries as well as in nanotechnology.
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The functions of lipids include storing energy, signaling, and acting as structural components of cell membranes.
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Non-polar solvents are typically hydrocarbons used to dissolve other naturally occurring hydrocarbon lipid molecules that do not (or do not easily) dissolve in water, including fatty acids, waxes, sterols, fat-soluble vitamins (such as vitamins A, D, E, and K), monoglycerides, diglycerides, triglycerides, and phospholipids. In biology and biochemistry, a lipid is a micro biomolecule that is soluble in nonpolar solvents. At the bottom is the common phospholipid phosphatidylcholine. : 328 The middle structure is a triglyceride composed of oleoyl, stearoyl, and palmitoyl chains attached to a glycerol backbone. At the top are cholesterol and oleic acid.