Question

Keeping in view the fluid mosaic model for the structure of cell membrane, which one of the following statements is correct with respect to the movement of lipids and proteins from one lipid monolayer to the other (described as flipflop movement)?

• A. While proteins can flip-flop, lipids can not.
• B. Neither lipids, nor proteins can flip-flop.
• C. Both lipids and proteins can flip-flop.
• D. While lipids can rarely flip-flop, proteins can not.

Answer 1

The correct option is D While lipids can rarely flip-flop, proteins can not.

Fluid mosaic model of membranes states that membrane components are free to diffuse in the plane of the membrane. Some of the membrane proteins are restricted to specific regions of the membrane by interactions with cytoskeletal proteins. Also, although many phospholipids and membrane proteins can move laterally within a leaflet, they do not flip-flop from one leaflet of the bilayer to the other. Flip-flop of the phospholipids is very rare. The inner and outer leaflets of the membrane may be made up of different phospholipids. Membrane fluidity refers to the movement of membrane phospholipids within the plane of the membrane. A decrease in fluidity is associated with decreased transport rates. The length of the fatty acid side chains also affects fluidity. The phospholipids with long hydrocarbon chains have increased hydrophobic interactions with neighboring lipids and thus decreased membrane fluidity. So, while lipids can rarely flip-flop, proteins can not.

So, the correct option is 'While lipids can rarely flip-flop, proteins cannot'.