Describe briefly the structure of plasma membrane.
- The plasma membrane is made up of lipids and proteins and is permeable.
- The membrane is generally about 7.5nm (75Å) thick.
- The membrane architecture is that of a pipid bilayer. The lipds are amphipathic in that they have hydrophilic polar (globular) heads pointing out and the hydrophobic nonpolar heads (straight) regions forming the core.
- Different proteins are embedded in the lipid bilayer. They may pass through the bilayer as transmembrane proteins or they may be inserted at the cytoplasmic or exterior face.
The uncharged, hydrophobic portions of the proteins are usually located in the interior of the membrane. The charged, hydrophilic portions of of the proteins are located on the surfaces. Peripheral proteins are attached to the surfaces of the membrane in various ways- e.g. (i) attachement to glycosylated forms of phosphatidylinositol. Proteins held by these glycosyl-phosphatidyl-inositol (GPI) anchors are alkaline phosphatase, various, various cell adhesion molecules, perforins which combat cell lysis by complement. More than 40 GPI – linked celll surface proteins have now been known (ii) some proteins are lipidated. They have specific lipids attached to them. Proteins may be myristolated, palmitoylated.