Waxes
Waxes are simple esters: one long-chain fatty acid + one long-chain alcohol. Both partners are long hydrocarbon chains, so waxes are hydrophobic, inert, and stable.
Structure
The fatty acid is usually 14-36 carbons. The alcohol is usually 16-36 carbons. Two very long tails = solid at room temperature and extremely water-repellent.
Examples
- Beeswax (triacontanyl palmitate and related esters) - comb of bees.
- Lanolin - on sheep wool, used in skin creams.
- Carnauba wax - from palm leaves, used to polish cars and surfboards.
- Plant cuticle - a waxy layer on leaves and fruit that prevents water loss.
- Ear wax (cerumen) - a mixture of wax esters, sebum, and dead cells that traps debris in the ear canal.
Function
Waxes are waterproofing and protective. The hydrocarbon chains form a tight, hydrophobic coating that water cannot penetrate.
What chemical groups make up a wax?
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A wax is a single ester between a long-chain fatty acid and a long-chain alcohol. Both chains are long hydrocarbon tails (typically 14-36 carbons each), making waxes extremely hydrophobic and water-repellent.
Why does a leaf have a waxy cuticle?
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The cuticle wax forms a hydrophobic coating on the leaf surface that prevents uncontrolled water loss. Without the waxy layer, the leaf would dehydrate quickly. Many fruits (apples, grapes) have similar cuticular waxes that can often be seen as a whitish bloom on the surface.