glycerophospholipid

Meaning: A glycerophospholipid is a lipid built on a glycerol backbone. Fatty acids are attached by ester bonds to carbons 1 and 2, and a phosphate on carbon 3 is linked to a polar head group such as choline, ethanolamine, serine, or inositol. The phosphate and head group form a hydrophilic head, and the two fatty acid chains form hydrophobic tails, so the molecule is amphipathic. In water these lipids assemble into bilayers with the tails turned inward, which is the basis of cell membranes.

On the MCAT: Passages ask you to identify the structure from a drawing or to predict how tail features change a membrane. Longer, saturated tails pack tightly and lower fluidity. Cis double bonds create kinks that disrupt packing and raise fluidity. Head group charge affects interactions with proteins and ions at the membrane surface. Expect questions on micelles versus bilayers: two-tailed lipids like glycerophospholipids favor bilayers, while single-tailed molecules such as soaps and free fatty acids favor micelles.

Common confusion: Some phospholipids are not glycerophospholipids. Sphingomyelin has a sphingosine backbone instead of glycerol, yet it is still a phospholipid. Triacylglycerols also have a glycerol backbone, but all three positions carry fatty acids and there is no phosphate, so they are nonpolar storage fats and do not form bilayers.