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In fact, soap works to remove oil and grease stains because it has amphipathic properties. Phospholipids are thus amphipathic molecules.Īn amphipathic molecule is one that contains both a hydrophilic and a hydrophobic region. This combination adds to the fluidity of the tails that are constantly in motion. Some lipid tails consist of saturated fatty acids and some contain unsaturated fatty acids. The lipid tails, on the other hand, are uncharged, or nonpolar, and are hydrophobic-or “water fearing.”Ī hydrophobic molecule (or region of a molecule) repels and is repelled by water. The phosphate heads are thus attracted to the water molecules of both the extracellular and intracellular environments. The phosphate group is negatively charged, making the head polar and hydrophilic-or “water loving.”Ī hydrophilic molecule (or region of a molecule) is one that is attracted to water. A single phospholipid molecule has a phosphate group on one end, called the “head,” and two side-by-side chains of fatty acids that make up the lipid tails (Figure 1). Cholesterol is also present, which contributes to the fluidity of the membrane, and there are various proteins embedded within the membrane that have a variety of functions. The cell membrane is an extremely pliable structure composed primarily of back-to-back phospholipids (a “bilayer”).

Unsaturated fatty acids result in kinks in the hydrophobic tails. Figure 1. Phospholipid Structure. A phospholipid molecule consists of a polar phosphate “head,” which is hydrophilic and a non-polar lipid “tail,” which is hydrophobic.