Question

According to widely accepted 'fluid mosaic model' cell membranes are semi-fluid, where lipids and integral proteins can diffuse randomly. In recent years, this model has been modified in several respects. In this regard, which of the following statements is incorrect?

• A. proteins in cell membranes can travel within the lipid bilayer.
• B. proteins can also undergo flip-flop movements in the lipid bilayer.
• C. proteins can remain confined within certain domains of the membrane.
• D. many proteins remain completely embedded within the lipid bilayer.

Answer 1

Answer: (B)

proteins can also undergo flip-flop movements in the lipid bilayer.

Answer 2

According to fluid mosaic model there is rapid internal motion involving flexing within each lipid molecule a rapid lateral diffusion of the lipids is possible and a slow 'flip-flop' motion, i.e., a transfer of lipid molecules from one side of the bilayer to the other, is also possible. The lipid molecules might also rotate about their axes. The proteins of the membrane are concerned with the enzymatic activity of the membrane, with transport of molecules, and with a receptor function whereas, the lipid bilayer provides the permeability barrier.