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= Lipids =

Introduction:
Lipids are one of the four types of biomolecules. A lipid is a small, naturally occurring molecule that has limited solubility in water being either hydrophobic (containing only polar groups) or amphipathic (possessing both polar and nonpolar groups). It can be isolated from an organism by extraction with a nonpolar organic solvent. Examples of lipids are fats, oils, waxes, some vitamins (vitamin A, E, D, and K), hormones, and nonprotein membrane components. There are many categories of lipids but the main ones discussed in this section will be fatty acids, triaclyglycerols, glycerophospholipids, sphingolipids, waxes, terpenes, and steroids.

Fatty Acids
A fatty acid is composed of a long hydrocarbon chain (tail) and terminal carboxyl group (head). The carboxyl group is normally ionized under physiological conditions. These occur in large amounts in biological systems and typically esterified to glycerol or other backbone structures. Fatty acids are either saturated in which all carbon-carbon bonds are single bonds and contain maximum number of bonded hydrogen, or unsaturated where there exist at least one or more double bonds in the hydrocarbon chain. If only one double bond exist it is called monounsaturatred, and if 2 or more double bonds exist it is called polyunsaturated. Free rotation around each carbon-carbon bonds make saturated fatty acids flexible compounds and found primarily solid at room temperature. Unsaturated are more prominent in nature especially in plants. These are found liquid at room temperature and numbers of double bonds typically range from one to four. The double bonds in unsaturated fatty acids are mostly found in nature as "cis" conformations.