Lipids

Lipids are a heterogeneous collection of components that share only one property: they are easily dissolved in organic solvents but can only hardly or not at all be dissolved in water. Among the lipids are:

fats and oils
waxes
phospholipids
glycolipids and
steroids

Fats and oils are complexes of saturated or unsaturated fatty acids and glycerol that are linked via ester bonds. The number of C-atoms in fatty acids is always even (mostly 16 and 18). This is caused by the biosynthesis of fatty acids where C₂-unities are combined to chains.

palmitic acid

oleic acid

Among the unsaturated fatty acids are compounds with one, two or three double bonds. Depending on how many fatty acid residues are carried by a glycerol-residue, it is distinguished between mono-, di- and triglycerides.

Triglycerides make up the chief amount of storage fats. Lipids with short fatty acid residues take part in the species-specific flavour of several fruits.

The esters of fatty acids with long-chained alcohols are called waxes. Their fatty acids are composed of rather long chains (24 - 36 C-atoms).

Phospholipids are counted among the complex lipids. They are essential structural elements of membranes. They have two fatty acids residues linked to glycerol. Depending on the molecule residue that is linked to the third hydroxyl-group of the glycerol via phosphate, it is distinguished between phosphatides, plasmalogenes and sphingolipids.

In glycolipids, the glycerol-residue carries a sugar instead of a phosphate. They are characteristic for plastid membranes.

A completely different group, the steroids, are also counted among the lipids. They will be dealt with later.

cholesterol

KEGG database - Compound Classification      Fatty acids   Fats   Phospholipids   Glycolipids   Steroid hormones   Other steroids   Eicosanoids

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© Peter v. Sengbusch - b-online@botanik.uni-hamburg.de

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