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According to the 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 can also undergo flip-flop movements in the lipid bilayer
B
Many proteins remain completely embedded within the lipid bilayer
C
Proteins in cell membranes can travel within the lipid bilayer
D
Proteins can remain confined within certain domains of the membranes
Detailed Solution
In the fluid mosaic model, the quasi-fluid lipid bilayer allows the lateral movement of proteins within the membrane; so proteins can travel within the bilayer.
Integral proteins may remain partly or completely embedded within the lipid bilayer, and some proteins are confined to particular domains of the membrane by attachment to the cytoskeleton.
Flip-flop is the transverse movement of a molecule from one monolayer to the other. Proteins are large and have extensive hydrophilic regions, which cannot pass through the hydrophobic core of the bilayer.
So proteins cannot undergo flip-flop movement; even lipids do so only rarely.
This is why the two faces of a membrane remain different (membrane asymmetry).
So the incorrect statement is that proteins can also undergo flip-flop movements in the lipid bilayer.
Integral proteins may remain partly or completely embedded within the lipid bilayer, and some proteins are confined to particular domains of the membrane by attachment to the cytoskeleton.
Flip-flop is the transverse movement of a molecule from one monolayer to the other. Proteins are large and have extensive hydrophilic regions, which cannot pass through the hydrophobic core of the bilayer.
So proteins cannot undergo flip-flop movement; even lipids do so only rarely.
This is why the two faces of a membrane remain different (membrane asymmetry).
So the incorrect statement is that proteins can also undergo flip-flop movements in the lipid bilayer.