Mechanism of Harmone Action
The hormones act in two ways –
On cell surface and within a cell.
(a) On cell surface : The molecules of hormones that are amino acid derivatives, peptides or proteins are large and insoluble in lipid, and can not enter the target cell. Therefore they act at the cell surface. They bind to specific receptor molecules located on the surface of cell membrane. The hormone receptor complex may acts in one of the two ways –
# (1) Formation of cAMP : Mechanism of formation of cAMP was discovered by E.W. Sutherland in 1950. The hormone receptor complex causes the release of an enzyme adenyl cyclase. From the receptor site. This enzyme hydrolise the ATP into c-AMP. The c-AMP activates the existing enzyme system of the cell. This accelerates the metabolic reactions in cell. The hormone is called first messenger and the c-AMP is termed the second messenger. e.g. Adrenaline causes the secretion of glucose from the liver cell from this mechanism.
# (2) Change in membrane permeability : The receptor proteins of some hormones are large transmembrane intrinsic protein acting as ion channels for facilitated diffusion of Na+, K+, Ca2+ etc. On binding with specific hormone these receptor proteins undergo conformational changes, so that the membrane permeability for ions is altered, resulting into important changes in metabolism.
- For example insulin promotes the entry of glucose from blood into the muscles cells by increasing the permeability of sarcolemma to glucose.
(b) Within a cell : The steroid hormones act within the cell. Their small, lipid soluble molecules pass through the cell membrane and bind to specific receptor molecules present in the cytoplasm. The receptor molecules carry them into the nucleus. Here, the receptor hormone complex binds to a specific receptor site on the chromosome and activates certain genes that were previously repressed. The activated gene transcribe m-RNA which directs the synthesis of enzyme (protein molecule) in the cytoplasm. The enzyme molecule promote the metabolic reactions in the cell.
On cell surface and within a cell.
(a) On cell surface : The molecules of hormones that are amino acid derivatives, peptides or proteins are large and insoluble in lipid, and can not enter the target cell. Therefore they act at the cell surface. They bind to specific receptor molecules located on the surface of cell membrane. The hormone receptor complex may acts in one of the two ways –
# (1) Formation of cAMP : Mechanism of formation of cAMP was discovered by E.W. Sutherland in 1950. The hormone receptor complex causes the release of an enzyme adenyl cyclase. From the receptor site. This enzyme hydrolise the ATP into c-AMP. The c-AMP activates the existing enzyme system of the cell. This accelerates the metabolic reactions in cell. The hormone is called first messenger and the c-AMP is termed the second messenger. e.g. Adrenaline causes the secretion of glucose from the liver cell from this mechanism.
# (2) Change in membrane permeability : The receptor proteins of some hormones are large transmembrane intrinsic protein acting as ion channels for facilitated diffusion of Na+, K+, Ca2+ etc. On binding with specific hormone these receptor proteins undergo conformational changes, so that the membrane permeability for ions is altered, resulting into important changes in metabolism.
- For example insulin promotes the entry of glucose from blood into the muscles cells by increasing the permeability of sarcolemma to glucose.
(b) Within a cell : The steroid hormones act within the cell. Their small, lipid soluble molecules pass through the cell membrane and bind to specific receptor molecules present in the cytoplasm. The receptor molecules carry them into the nucleus. Here, the receptor hormone complex binds to a specific receptor site on the chromosome and activates certain genes that were previously repressed. The activated gene transcribe m-RNA which directs the synthesis of enzyme (protein molecule) in the cytoplasm. The enzyme molecule promote the metabolic reactions in the cell.
