Question

Why do phospholipids form a bilayer in water-based solutions?

Answer 1

Answer: Phospholipids as the name suggests are the lipid molecules with an attached phosphate group. They have a head part and two tails. The head part is the phosphate group and the tail parts are the fatty acid chains.

These lipid molecules are amphipathic in nature i.e. they have hydrophilic part (polar head) and hydrophobic part (non polar tails)

The head part is polar because of the negatively charged phosphate group which is the hydrophilic or the water loving part.

Whereas the tails are the fatty acid chains which are uncharged i.e. non polar and are hydrophobic or water fearing i.e. the chains will orient themselves in such a way that they are away from water in the aqueous environment.

When there are two layers of phospholipids in the environment of water the hydrophobic ends of the two layers will come face to face and the head parts of the two layers will remain in contact with water. This way the hydrophobic ends are shielded from water and the hydrophobic tails are sandwiched between the hydrophilic heads, this closing in on the hydrophobic ends in the interior makes the structure energetically favourable and hence the phospholipid forms a bilayer in water based solutions.

Note: phospholipids are the major components of the biological membranes where because of the bilayer structure the head parts of one layer faces outside the cell and head part of another layer faces the cytoplasm with hydrophobic tails forming the interior of the membrane.