Lipid | Definition, Structure, Examples, Functions, Types, & Facts

Home » What Elements Are Found In Lipids » Lipid | Definition, Structure, Examples, Functions, Types, & Facts

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Structure

stearic acid
stearic acidStructural formula of stearic acid.(more)

Biological fatty acids, members of the class of compounds known as carboxylic acids, are composed of a hydrocarbon chain with one terminal carboxyl group (COOH). The fragment of a carboxylic acid not including the hydroxyl (OH) group is called an acyl group. Under physiological conditions in water, this acidic group usually has lost a hydrogen ion (H+) to form a negatively charged carboxylate group (COO−). Most biological fatty acids contain an even number of carbon atoms because the biosynthetic pathway common to all organisms involves chemically linking two-carbon units together (although relatively small amounts of odd-number fatty acids do occur in some organisms). Although the molecule as a whole is water-insoluble by virtue of its hydrophobic hydrocarbon chain, the negatively charged carboxylate is hydrophilic. This common form for biological lipids—one that contains well-separated hydrophobic and hydrophilic parts—is called amphipathic.

Key People: Pieter Cullis (Show more) Related Topics: glyceride lipopolysaccharide leukotriene chylomicron thromboxane (Show more) See all related content

In addition to straight-chain hydrocarbons, fatty acids may also contain pairs of carbons linked by one or more double bonds, methyl branches, or a three-carbon cyclopropane ring near the centre of the carbon chain.

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