Up regulation and down regulation with examples

Down regulation

o   Is the process by which a cell decreases the quantity of a cellular component, such as RNA or protein in response to an external variable.

o   There are several ways in which a cell down regulates its cellular components.

1.      Receptor mediated endocytosis.

Occurs when the material to be transported into the cell binds to certain specific molecules in the membrane. Common cause for down regulation in membrane receptor. 

2.      Internalization.

Ligands bind to their receptors and ligand-receptor complex move laterally in the membrane to coated pits where they are taken into the cell by endocytosis. Some receptors are recycled and some replaced by de nova synthesis. 

3.      Desensitization.

Receptors are chemically modified in ways that make them less responsive.

Ex-:      Increase in plasma insulin in NIDDM(type11) .

Down regulation of PTH receptors in the parathyroid gland when PTH increases.

Up regulation

o   Is the process by which a cell increases its cellular components in response to an external variable.

Ex:-      Number of the cyt P₄₅₀ enzyme in liver cells are increased when xenobiotics molecules such as dioxin are administered resulting in greater degradation of xenobiotics.