Question

The plasma membrane is very important to the cell.

a. Draw and describe the structure and function of the plasma membrane.

b. What is the chemical explanation for the structure of the plasma membrane?

c. Diagram and four different transport mechanisms across the membrane, and then compare and contrast the benefits and drawbacks of each mechanism to the cell:

Answer 1

The plasma membrane is made up of 2 layers of phospholipids. Therefore it is also called as phospholipid bilayer. Each molecule of phospholipid is amphipathic in nature because it contains both hydrophilic and hydrophobic molecules. It has a hydrophilic or water soluble phosphate head. It also have two hydrophobic fatty acid tails which are water in soluble. These fatty acid tails can be saturated or unsaturated in nature. The saturation level of fatty acid tails determine the level of compaction of phospholipid bilayer.

There are two types of protein in the phospholipid bilayer. Intrinsic proteins or integral or transmembrane proteins which are embedded inside the membrane. They span both extracellular and intracellular region of the plasma membrane. They are mainly receptors. Another type of protein is extrinsic protein or peripheral proteins which are located only on the surface of the plasma membrane, either on the extracellular surface or on the intracellular surface.

Apart from these proteins cholesterol molecules are present in the lipid bilayers. Cholesterol molecules are large sized molecules and therefore responsible for loosening of the plasma membrane.

The surface of the plasma membrane contains various signalling molecules like glycolipids and glycoproteins which are involved in cell-to-cell interaction.

In the lipid bilayer there are areas which are rich in lipids only. These areas are called as lipids rafts.

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