21. Lipids and Carbohydrates   Previous PageNext Page
       Membrane Structure

Waxes are esters of very long fatty acids (26 to 34 carbons) and monohydroxy alcohols. They serve as waterproof protective coatings on the outsides of leaves and fruit, and on skin, fur, and feathers of animals. They are classed as lipids because their long hydrocarbon tails make them insoluble in water, but soluble in organic solvents such as benzene.

Fatty acid derivatives are not the only kind of lipids. Terpenes are volatile oils in plants that can be thought of as being built from units of isoprene, C5H8 (above). Terpenes extracted from geranium, citronella, bay, lemon, mint, pine, and many other sources, are highly aromatic in the true meaning of the word, but are not necessarily "aromatic" in the special way that chemists have appropriated the term to indicate delocalized ring compounds.

A few typical terpenes are shown here, with dashed lines to show how each molecule can be divided into isoprene-sized units. The b-carotene molecule, and the phytol tail on the chlorophyll molecule are long-chain terpenes.

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