Lipids

Condensation of ketoacyl units can form fatty acids, glycerolipids, glycerophospholipids, sphingolipids, saccharolipids, and polyketides.  Importantly, the way the molecules are linked together to form the polymer leaves a hydrophilic (polar) head and a hydrophobic (nonpolar) tail that is insoluble in water.  This means the carbon chain is between four and twenty-four carbons long.

Unsaturation (double bonds) cause the chain to bend which plays an important role in the structure and function of cell membranes.  Most naturally-occurring fatty acids are in the bent configuration.

http://www.sigmaaldrich.com/content/dam/sigma-aldrich/docs/Supelco/General_Information/t408126.pdf

When three fatty acids combine with a glycerol backbone, the triglyceride molecule is formed.  This is an energy store, comprising the bulk of storage fat in animal tissues.  Glycosylglycerols have sugar residues attached to glycerol, found in plant membranes and mammalian sperm cells.

Glycerophospholpids are part of the lipid bilayer of cells and may be membrane-derived second messengers.  Sphingolipids (from serine) are amide-linked fatty acids.  Molecules of this type are found across living systems; mammals (ceramide phosphocholine), insects (ceramide phosphoethanolamine), and fungi (phytoceramide phosphoinositols) which can be decorated via a glycosidic bond to the sphingoid base with a mannose for example.  Other examples include cerebrosides and gangliosides.

Condensation of isoprene units results in sterols and prenols.  Sterol lipids include membrane lipids and hormones: estrogen, testosterone, andosterone, glucocortiocorticoids, secosteroids (Vitamin D), stigmasterol, brassicasterol, ergosterol, etc. which are found in both humans and plants.

Prenol lipids, formed by the mevalonic acid pathway, result in terpenes, carotenoids, quinones, hydroquinones, ubiquinones, dolichols, etc.

Saccharolipids are disaccharides of glucosamine, decorated with as many as seven fatty-acyl chains.  This is a component of the growth medium for E. coli.

Polyketides are a class of secondary metabolites from animal, plant, bacterial, fungal, and marine sources having great structural diversity.  These molecules result via polymerization of acetyl and propionyl subunits.