Biology · Ch 6 — Biomolecules
Compound Lipids
Compound Lipids
Compound lipids are esters of fatty acids that carry, in addition, some other chemical group — phosphate in the case of phospholipids, a sugar in the case of glycolipids.
A phospholipid molecule is built from one glycerol, two fatty-acid chains, and a phosphate group (some phospholipids, such as lecithin, also carry a nitrogenous compound attached to the phosphate). This gives the molecule a distinctive dual character: a hydrophilic (water-attracting) polar 'head' formed by the phosphate and any nitrogenous group, and a hydrophobic (water-repelling) non-polar 'tail' formed by the two fatty-acid hydrocarbon chains. It is exactly this dual (amphipathic) character that lets phospholipids spontaneously assemble into the lipid bilayer that forms the basic structural fabric of every cell membrane — polar heads facing outward into the surrounding watery medium on both sides, and non-polar tails packed together, hidden from water, in the interior of the membrane. …
What this figure shows. A cross-section of a phospholipid bilayer in water: two layers of phospholipid molecules arranged tail-to-tail, each drawn with a circular polar head group facing the surrounding water on both outer faces, and two non-polar hydrocarbon tails pointing inward, away from water, forming the hydrophobic cor …