Question

Describe in detail the fluid-mosaic model of the plasma membrane and how the phospholipid cotent affects membrane fluidity? How is membrane fluidity assessed?

Answer 1

Fluid mosaic model: According to fluid mosaic model, cell membrane is composed of bunch of different molecules that are distributed across the membrane. These different type of molecules putting togather known as mosaic. These different molecules constantly move in two dimensions like in fluid fashion. The movement of the mosaic of the molecules gives fluidity to the membrane.

The three main molecules of the plasma membrane are: Phospholipids, Proteins and cholesterol. Phospholipids composed of two parts: Head and tail. Heads are phosphate molecule which are hydrophilic and attract water molecule and tails are hydrocarbon which are hydrophobic and repel wateer molecule. Tail contain single (saturated) and double (unsaturated) bond. Cellular membrane assemble into a lipid bilayer due to the hydrophilic and hydrophobic properties of phospholipids. The single bond make the tail straight and easy to pack tightly. Double bonds present in the tail form kink either in cis form or in trans form. The kinks play a role in membrane fluidity, because the kinks increase the space in between the phospholipids, making them harder to freeze at lower temperatures.

Cholesterol: The cholesterol molecules are randomly distributed across the phospholipid bilayer, helping the bilayer stay fluid in different environmental conditions.

Proteins: Protein molecules help transportation across plasma membrane.