Steps of the action of most nonsteroid hormones:
- Nonsteroid hormones are secreted by endocrine glands.
- Blood carries hormone molecules through the body.
- Hormone combines with the receptor site on the membrane of its target cell, activating G protein.
- Adenylate cyclase molecules are activated in the target cell's membrane.
- Adenylate cyclase converts ATP into cyclic AMP ( cyclic AMP is used as a second messenger by many hormones).
- Cyclic AMP activates protein kinases.
- Protein kinases activate protein substrates in the cell that change metabolic processes.
- Cellular changes produce the hormone's effects.
Explanation:
Nonsteroids include amines, peptides, proteins, and glycoproteins. Nonsteroid hormones are primarily derived from proteins and are water soluble due to their polar nature. These hormones are transported freely through the blood. Non-steroid hormones interact with receptors on the target cell membrane. Each of these receptors has a binding site and an activity site; the binding site combines with a hormone and activity site interacts with other membrane proteins. This first step is triggered by a hormone called the first messenger. Non-steroid hormones interact with receptors on the cell membrane and activate secondary messenger systems that carry out their effects within the cell. Cyclic AMP is used as a second messenger by many hormones. In this mechanism, a hormone binds to its receptor; the resulting hormone-receptor complex activates a G protein- responsible for activation of adenylate cyclase, which removes two phosphates from ATP, reconnects the exposed oxygen and forms cyclic AMP. Cyclic AMP plays a role in the activation of protein kinases, which modify the function of other proteins by attaching phosphate groups to them. This process is called phosphorylation and activates protein substrates in the cell that change metabolic processes. Phosphorylation activates some proteins and renders others inactive. Certain nonsteroid hormones use second messenger other than cAMP. Diacylglycerol is the second messenger which activates protein kinase and leads to a cellular response. Inositol triphosphate is the second messenger which releases calcium ions from internal stores within the cell's endoplasmic reticulum; these calcium ions are required for activation of the protein calmodulin, which interacts with enzymes altering their activities. Another hormonal mechanism uses cyclic guanosine monophosphate s a second messenger.
