lipid (redirected from Lipid A)

lipid

Any of a diverse class of organic compounds, found in all living things, that are greasy and insoluble in water. One of the three large classes of substances in foods and living cells, lipids contain more than twice as much energy (calories) per unit of weight as the other two (proteins and carbohydrates). They include the fats and edible oils (e.g., butter, olive oil, corn oil), which are primarily triglycerides; phospholipids (e.g., lecithin), which are important in cell structure and metabolism; waxes of animal or plant origin; and sphingolipids, complex substances found in various tissues of the brain and nervous system. Since insolubility is the defining characteristic, cholesterol and related steroids, carotenoids (see carotene), prostaglandins, and various other compounds are also classifiable as lipids.

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lipid, lipide

Biochem any of a large group of organic compounds that are esters of fatty acids (simple lipids, such as fats and waxes) or closely related substances (compound lipids, such as phospholipids): usually insoluble in water but soluble in alcohol and other organic solvents. They are important structural materials in living organisms

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lipid [′lip·əd]

(biochemistry)

One of a class of compounds which contain long-chain aliphatic hydrocarbons and their derivatives, such as fatty acids, alcohols, amines, amino alcohols, and aldehydes; includes waxes, fats, and derived compounds. Also known as lipin; lipoid.

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Lipid

One of a class of compounds which contains long-chain aliphatic hydrocarbons (cyclic or acyclic) and their derivatives, such as acids (fatty acids), alcohols, amines, amino alcohols, and aldehydes. The presence of the long aliphatic chain as the characteristic component of lipids confers distinct solubility properties on the simpler members of this class of naturally occurring compounds.

The lipids are generally classified into the following groups:

• A. Simple lipids
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  • 1. Triglycerides or fats and oils are fatty acid esters of glycerol. Examples are lard, corn oil, cottonseed oil, and butter.
  • 2. Waxes are fatty acid esters of long-chain alcohols. Examples are beeswax, spermaceti, and carnauba wax.
  • 3. Steroids are lipids derived from partially or completely hydrogenated phenanthrene. Examples are cholesterol and ergosterol.
•  B. Complex lipids
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  • 1. Phosphatides or phospholipids are lipids which contain phosphorus and, in many instances, nitrogen. Examples are lecithin, cephalin, and phosphatidyl inositol.
  • 2. Glycolipids are lipids which contain carbohydrate residues. Examples are sterol glycosides, cerebrosides, and plant phytoglycolipids.
  • 3. Sphingolipids are lipids containing the long-chain amino alcohol sphingosine and its derivatives. Examples are sphingomyelins, ceramides, and cerebrosides.

Lipids are present in all living cells, but the proportion varies from tissue to tissue. The triglycerides accumulate in certain areas, such as adipose tissue in the human being and in the seeds of plants, where they represent a form of energy storage. The more complex lipids occur closely linked with protein in the membranes of cells and of subcellular particles. More active tissues generally have a higher complex lipid content; for example, the brain, liver, kidney, lung, and blood contain the highest concentration of phosphatides in the mammal. See Fat and oil, Fat and oil (food), Glycolipid, Sphingolipid, Steroid, Terpene, Triglyceride, Vitamin, Wax, animal and vegetable