Question

5b. Students now understand the structure of a phospholipid but want to know why there are so many head group options. They have already heard about sphingolipids. How would you explain to your students the reasoning behind so many types of lipids that make up the membranes of the cell? (5)

Answer 1

Phospholipids biolayer of the cell membrane has two portions1. The exposed hydrophilic portion (either to the outside environment or to inside cytosol). Based the backbone of the phospholipids there are mainly 2 kinds such as 1. Glycerophospholipids 2. Sphingolipids and in which the basic structure of these lipids are similar to having either a Glycerol or Sphingosine as the foundation moiety. Whereas in the case of head groups (lipids head groups are substitute that attached to foundation moiety), Glycerophospholpids carrying alcohol as the head group molecule and Shingolipids carrying either Choline or mono/oligosaccharides as the head groups molecule exposed to the surface. The vast diversity of head groups enable the cell membrane to recognize and bind with a diverse group of ligands approached to cell and thus it allows the possibility of carrying a wide range of functions such as cell signalling substrate transport etc. More specifically, in the case of Glycerophopholipids, the common head groups are in the alcohol category and are ethanolamine, Choline, Serine, etc. and where these head groups containing Glycerophospholipids carry out diverse functions such as 1. Ethanolamine and Choline act as chaperons thus mediating membrane-mediated cell signalling, 2. Serine is involved in apoptosis. In the case of Sphingolipids, the common head groups is in the Glycerol/Sphingosine category are Phosphocoline, Glucose etc. The functions of Phosphocoline containing Sphingolipids are involved in cell signalling pathways. Hence it is concluded that for carrying our diverse functions different head groups are attached to phospholipids backbone.