Multiple choice

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?

  1. Proteins can also undergo flip–flop movements in the lipid bilayer.

  2. Many proteins remain completely embedded within the lipid bilayer.

  3. Proteins in cell membranes can travel within the lipid bilayer.

  4. Proteins can remain confined within certain domains of the membrane.
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A Correct answer
Explanation

 Most large proteins do not flip-flop due to their extensive polar regions, which are unfavorable in the hydrophobic core of a membrane bilayer. This allows the asymmetry of membranes to be retained for long periods, which is an important aspect of cell regulation.

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