Question

•Plasma membrane (asymmetric) is derived from ER membrane (symmetric). How is a symmetric membrane converted into an asymmetric one?

•How might the asymmetric distribution of lipids in the plasma membrane contribute to its function?

Answer 1

1). Plasma membrane is the outer layer of cells, which surrounds the cytoplasm and regulates the movements of materials to and out of the cell. Both prokaryotes and eukaryotes contain plasma membrane and is a phospholipid bilayer. Within the phospholipid bilayer, proteins are embedded, according to fluid-mosaic model; the protein molecules embedded in the plasma membrane have a mosaic pattern.

Fluid mosaic model describes that two-dimensional lipid later of cell membrane where proteins are distributed like mosaic model in the phospholipid bilayer. This model is mostly accepted by biologists. According to this model, along the cell membrane, the proteins move laterally and the lipid distribution is asymmetrical. The "lipid asymmetry" in the membranes lipids is due to the different lipid compositions in the inner leaflet and the outer leaflet of a bilayer.

The synthesized phospholipids are initially inserted into the inner leaflet or inner monolayer, and those that constitute the outer monolayer are transported from the inner layer by means of flippases. The outer leaflet is rich in glycolipids. Outer leaflet is rich in glycolipids and the negatively charged phosphatidylserine (PS-) is uniformly distributed in the inner leaflets, which makes the inner leaflet more negative.