Question

Describe the structure and function of a cell’s plasma membrane.

Answer 1

STRUCTURE

1. The plasma membrane contains both proteins and lipids.
2. Most membrane associated lipids are structurally asymmetric with polar and non- polar ends and are called amphipathic.
3. The polar ends interact with water and are hydrophilic.
4. The non-polar ends are insoluble in water and tend to associate with one another.  This property of lipids enables them to form a lipid bilayer in membranes.
5. The outer surfaces are hydrophilic, whereas the hydrophobic ends are buried in the  interior away from the surrounding water.
6. Many of these amphipathic lipids are phospholipids.
7. The most widely accepted model for plasma membrane structure is the fluid mosaic  model  of Singer and Nicholson.
8. They distinguish between two types of membrane proteins.
   1. Peripheral proteins: These are loosely connected to the membrane and can be easily  removed. They are soluble in aqueous solution and make up 20-30% of total  membrane proteins. About 70-80% of membrane proteins are integral proteins.
   2. Integral proteins: These are amphipathic. Their hydrophobic regions are buried in  the lipid while the hydrophobic portions project from the membrane surface.

FUNCTIONS

1. Indispensible for the cell.
2. Acts as a selectively permeable barrier.
3. Allows only particular ions and molecules to pass either in and out of the cell, while  preventing the movement of others.
4. Prokaryotic plasma membrane is the location of a variety of crucial metabolic  processes like  photosynthesis and respiration.
5. Bacterial cell membranes house ETS.
6. Prokaryotic plasma membrane contains special receptor molecules that help  prokaryotes detect and respond to chemicals in their surroundings.
7. Plasma membrane also houses the enzyme ATPase which helps in synthesis of ATP.