Question

In fluid mosaic model of plasma membrane

• A. Upper layer is non-polar and hydrophilic
• B. Polar layer is hydrophobic
• C. Phospholipids form a bimolecular layer in middle part
• D. Proteins form a middle layer

Answer 1

The correct option is C Phospholipids form a bimolecular layer in middle part

According to the fluid mosaic model, the cell membrane consists of a highly viscous fluid matrix of two layers of phospholipid molecules. Protein molecules (or their complexes) occur in the membrane but not in a continuous layer. Chemically a biomembrane consists of lipids (20-70%), proteins (20-70%), carbohydrates (1-5%) and water (20%). The important lipids of the membrane are phospholipids (some hundred types), sterols, (e.g. cholesterol), glycolipids, sphingolipid (e.g., sphingomyelin, cerebrosides). Protein can be a fibrous or globular structural carrier, receptor or enzymatic. The lipid molecules are amphiatic or amphipathic, that is, they possess both polar hydrophilic (water-loving) and non-polar hydrophobic (water-repelling) ends. The hydrophilic region is in the form of the head while the hydrophobic part contains two tails of fatty acids. It results in the formation of a lipid bilayer. The most common lipid of the bilayer is phospholipids. Protein molecules also possess both polar and non-polar side chains. Usually, their poly hydrophilic linkages are towards the outer side. The non-polar or hydrophobic linkage is either kept folded inside or used to establish connections with hydrophobic parts of the lipids.

So, the correct answer is 'Phospholipids form a bimolecular layer in middle part'.