Summarizing Lipids

Summary of lessons so far

Lipids are a class of macromolecules that are nonpolar and hydrophobic in nature. In general, major types include fats and oils, waxes, phospholipids, and steroids. Fats are a stored form of energy and are also known as triacylglycerols or triglycerides. Fats are made up of fatty acids and either glycerol or sphingosine.

Fatty acids may be unsaturated or saturated, depending on the presence or absence of double bonds in the hydrocarbon chain. If only single bonds are present, they are known as saturated fatty acids. Unsaturated fatty acids may have one or more double bonds in the hydrocarbon chain.

Phospholipids make up the matrix of membranes. They have a glycerol or sphingosine backbone to which two fatty acid chains and a phosphate-containing group are attached.

Steroids are another class of lipids. Their basic structure has four fused carbon rings. Cholesterol is a type of steroid and is an important constituent of the plasma membrane, where it helps to maintain the fluid nature of the membrane. It is also the precursor of steroid hormones such as testosterone.

Glossary of Words


macromolecule that is nonpolar and insoluble in water

Omega fat

type of polyunsaturated fat that is required by the body; the numbering of the carbon omega starts from the methyl end or the end that is farthest from the carboxylic end


major constituent of the plasma membranes; composed of two fatty acids and a phosphate-containing group attached to a glycerol backbone

Saturated fatty acid

long-chain of hydrocarbon with single covalent bonds in the carbon chain; the number of hydrogen atoms attached to the carbon skeleton is maximized


type of lipid composed of four fused hydrocarbon rings forming a planar structure

Trans fat

fat formed artificially by hydrogenating oils, leading to a different arrangement of double bond(s) than those found in naturally occurring lipids

Triacylglycerol (also, triglyceride)

fat molecule; consists of three fatty acids linked to a glycerol molecule

Unsaturated fatty acid

long-chain hydrocarbon that has one or more double bonds in the hydrocarbon chain


lipid made of a long-chain fatty acid that is esterified to a long-chain alcohol; serves as a protective coating on some feathers, aquatic mammal fur, and leaves

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