Question

According to the widely accepted “fluid mosaic model” cell membranes are semi-fluid, where lipids and integral proteins can diffuse randomly. In recent years, this model has been modified in several respects. In this regard, which of the following statements are incorrect-
A. Proteins can undergo flip flop movements in the lipid bilayer.
B. Many proteins remain completely embedded within the lipid bilayer.
C. Proteins in cell membranes can travel within the lipid bilayer.
D. Proteins can remain confined within certain domains of the membrane.

Answer 1

Hint:Cell membrane is the structure of the cell that forms a covering around the cell and helps the cell to take up essential nutrients and remove waste from the cell. To study and explain the structure of the cell membrane (also known as the plasma membrane) fluid mosaic model was proposed.

Complete answer:
The cell membrane holds the components of the cell inside and acts as a protective barrier from the outside environment letting selective substances enter inside and outside the cell. In 1972, the fluid mosaic model was first proposed by S.J. Singer and G.L. Nicolson. According to this model cell membrane is made up of three main components, phospholipids, cholesterol, and proteins.
The phospholipid bilayer is made of individual phospholipids arranged themselves into two layers with their heads (phosphate molecule, that is polar and hydrophilic) pointing outwards and their tails (two tails are made up of fatty acids with no charge and are hydrophobic) pointing inwards.
Cholesterol is a special molecule made in the liver that regulates the fluidity and permeability of the cell membrane as it causes the phospholipids to stay closer to each other.
The protein present in the cell membrane are of different types; integral proteins: helps in transportation of large molecules across the cell membrane depending upon the concentration gradient through protein channels, peripheral proteins are involved in cell communication and transport of some molecules, and third is a glycoprotein, these are important in the immune system as it plays a vital role in cell recognition. The fluidity cell membrane allows flip flop movement of the proteins.

Hence, the correct option will be option A - Proteins can undergo flip flop movements in the lipid bilayer.

Note: The fluidity of the cell membrane is a perfect balance between passages of molecules outside or inside the cell and also it is not that fluid that it cannot hold the cell. Fluidity allows selective transmission of essential substances, as well as serves, which are a protective layer that holds the cell intact. This is due to the lipid bilayer present in it.