Question

The site of action of Insulin is:
A. Mitochondria
B. Nucleus
C. Plasma membrane
D. DNA

Answer 1

Hint: Insulin, a type of peptide hormone regulates the blood glucose level in the body. It helps to transport glucose from the blood to different parts of the body to be used for energy. The organelle which is responsible for transportation of material is the proper site of action for this hormone.

Step by step answer: Insulin, a peptide hormone is produced in the $\beta $ cells of the pancreas. It is a critical regulator at the transcriptional and translational levels which mediates transportation of glucose to different cell organelles via bloodstream in the body for the requirement of the energy. Insulin is synthesized as a preproinsulin and proinsulin which is then converted to insulin and stored in secretory granules and releases when required.

Insulin regulates the metabolism of carbohydrates, proteins, fats by promoting the absorption of glucose from the blood into the liver. The absorbed glucose is converted into glycogen and remains stored until being required for the use.

Plasma membrane is a phospholipid bilayer cell organelles embedded with different type of transporter proteins in it. The various proteins embedded in the phospholipid bilayer penetrate in and out of the layer responsible for the transportation of molecules in and out of the cells.

Insulin gets binded to a glycoprotein receptor on the surface of the carrier protein of the plasma membrane .These receptors have alpha-subunits which bind the hormone insulin and get stimulated with the help of tyrosine –protein kinase. This carrier protein triggers the movement of bounded molecules from the outside of the cell to its interior, depending upon the concentration gradient of the material. When any cell organelle calls out for the energy the insulin hormone transports the stored glycogen from the liver through the bilayer of the plasma membrane.

Therefore, the plasma membrane is the site of action of insulin.
Hence the correct option is option (C).

Note: Plasma membrane is responsible for the active and passive transportation across the cell. The transportation takes place through the diffusion process in which molecules move from the higher concentration to the lower concentration.