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Examples of second messenger molecules include cyclic AMP, cyclic GMP, inositol triphosphate, diacylglycerol, and calcium. [2] First messengers are extracellular factors, often hormones or neurotransmitters, such as epinephrine, growth hormone, and serotonin.
Lipophilic second messenger molecules are derived from lipids residing in cellular membranes; enzymes stimulated by activated receptors activate the lipids by modifying them. Examples include diacylglycerol and ceramide , the former required for the activation of protein kinase C .
Calcium is a ubiquitous second messenger with wide-ranging physiological roles. [2] These include muscle contraction , neuronal transmission (as in an excitatory synapse ), cellular motility (including the movement of flagella and cilia ), fertilization , cell growth (proliferation), neurogenesis , learning and memory as with synaptic ...
Typically the final effect consists in the activation of an ion channel (ligand-gated ion channel) or the initiation of a second messenger system cascade that propagates the signal through the cell. Second messenger systems can amplify or modulate a signal, in which activation of a few receptors results in multiple secondary messengers being ...
For example, binding of G proteins to receptors affects the receptor's affinity for ligands. Activated G proteins are bound to GTP. Further signal transduction depends on the type of G protein. The enzyme adenylate cyclase is an example of a cellular protein that can be regulated by a G protein, in this case the G protein G s. Adenylate cyclase ...
Signal transduction is realized by activation of specific receptors and consequent production/delivery of second messengers, such as Ca 2+ or cAMP.These molecules operate as signal transducers, triggering intracellular cascades and in turn amplifying the initial signal. [4]
Examples are the class of nuclear receptors located in the cell nucleus and cytoplasm and the IP 3 receptor located on the endoplasmic reticulum.The ligands that bind to them are usually intracellular second messengers like inositol trisphosphate (IP 3) and extracellular lipophilic hormones like steroid hormones.
A general second messenger system mechanism can be broken down into four steps. First, the agonist activates a membrane-bound receptor. Second, the activated G-protein produces a primary effector. Third, the primary effect stimulates the second messenger synthesis. Fourth, the second messenger activates a certain cellular process.