Question

Write a well composed paragraph using complete sentences that explains the structure of the cell membrane and then explains how it acts as a gatekeeper to the cell.

Answer 1

The cell membrane also called the plasma membrane is made up of the lipid bilayer ( Fluid Mosaic Model). It is dynamic, fluid-structure, and form the external boundary of the cell. Is selectively permeable and regulates the molecular traffic across the boundary and that too of some specific solutes.

As per the Fluid Mosaic Model (most accepted model), membranes are viewed as a quasi-fluid structure in which proteins are inserted. It is called the fluid mosaic model because embedded proteins provide the mosaic arrangement and the lipids provide fluidity.

Chemically, the ratio of the lipids and proteins varies as per cell type e.g. in human RBCs lipid content is 43% and protein content is 49%. Carbohydrates when bounded to proteins are called glycoproteins and when bound with the lipids then called glycolipids.

The lipid bilayer is composed of the two leaflets of amphipathic lipid molecules, whose polar heads interact with the intra- or extracellular aqueous phase and their tails face each other forming hydrophobic interior of the membrane (hydrophobic interactions are involved). Three classes of lipid molecules are present in a lipid bilayer: Phospholipid, Glycolipid, and sterol.

Transportation is facilitated by the protein channels called a carrier or channel proteins. These can be uniporters or co-transporters - these transport single solute at a time. Co transport mediate coupled transport - when is the same direction called symport and when in opposite directions called as uniport.