Question

Cell membrane mainly consist of
A) Carbohydrates bilayer and proteins
B) Proteins bilayer and phospholipids
C) lipid bilayer and proteins
D) None of these

Answer 1

Hint: Cell membrane is basically the outer covering of the cell which should be made up of more than one layer to protect the inner organelles. Adding to it is, one should know that it is selectively permeable to the substances. It helps in the movement of molecules and ions in and out of the cell.

Complete answer:
The first model of the cell membrane was proposed by Singer and Nicolson are widely known as the fluid mosaic model. According to which the quasi- fluid nature of lipid enables the movement of protein in the bilayers. This helps to increase the fluidity in the membrane.

The structure of the cell membrane is made up of lipids that are arranged in bilayer and protein. The lipids are arranged within the membrane with the polar head towards the outer sides and the hydrophobic tails toward the inner side. This ensures that the nonpolar tail of saturated hydrocarbons is protected from the aqueous environment. The lipids usually contain phosphoglycerides.

The fluid nature of the membrane helps in the functions of cell growth, formation of intercellular junctions, secretion, cell division etc. The ratio of protein and lipid varies considerably from cell to cell. In Human beings, the percentage is approx 52% of protein and 40% of lipids.

On the basis of ease of extraction, membrane proteins can be classified into integral and peripheral.
INTEGRAL - These proteins are partially or totally buried in the membrane.
PERIPHERAL- These proteins lie on the surface of the membrane.
The carbohydrates are found on the outer surface of the plasma membrane. They are either bound to lipids or proteins.

Thus the correct answer is option ‘C’.

Note: The main function of the membrane is the transport of the molecules across it. The cell membrane helps transport the molecules across without the requirement of energy. The channel proteins help in the transport of polar molecules. Similarly, water transportation between them takes place through osmosis.