Question

A scientist isolated the plasma membrane from some animal cells and put them in a solution of chemicals that stabilised the membranes. When she added a small amount of a salt solution, she discovered that although the membranes seemed intact, the amount of protein in the stabilising solution had increased. These new proteins in the stabilising solution were probably

• A. Peripheral proteins
• B. Integral proteins
• C. Lipid-anchored proteins
• D. Trimetric G proteins

Answer 1

The correct option is A Peripheral proteins

The main lipid components of the plasma membrane are phospholipids, cholestrol and galactolipids; their proportion varies in different cell membranes. According to fluid-mosaic model, lipid molecules are present in viscous bilayer and protein molecules occur at place both inside and on outer side the lipid bilayer. Intrinsic or integral proteins represent more than 70% of the membrane proteins. They are insoluble in water solutions, and are associated with lipids. They attach to oligosaccharides to form glycoproteins. They pass into the lipid bilayer to different depths and establish hydrophobic bonds with lipid molecules. Some of the integral proteins run throughout the lipid bilayer. The extrinsic or peripheral proteins are superficially on the two surfaces of the membrane, more on the cytosolic face than on the external face. Peripheral proteins are separated by mild treatment with high ionic strength or with metal chelating agents, are soluble in aqueous solution and are usually free of lipids, for example, spectrin.

So, the correct answer is 'Peripheral proteins'.