Primary messengers

Fig. 2. Activation of an intracellular PLC by an extracellular signal (primary messenger) transduced across the membrane via a receptor and G-protein. The products DAG and IP3 that are produced by the PLC catalyzed hydrolysis of phospholipids are secondary messengers...

Incompletely spliced primary messenger, as well as unprocessed genomic material, may be present as impurities in a mRNA preparation and may obscure the alignment of autologous ESTs necessary for finding variants. 

The cyclic nucleotides adenosine 3, 5 -cyclic monophosphate (cyclic AMP (cAMP)) and guanosine 3, 5 -cyc.lic monophosphate (cyclic GMP (c.GMP)) are second messengers generated by adenylyl (adenylate) cyclase (AC) and guanylyl (guanylate) cyclase (GC), respectively, in response to receptor occupation by particular primary messengers , that is,... 

Protein phosphorylation alters protein ligand binding and/or catalytic functions and hence specific cellular processes, this representing the cellular response to the stimulus of the original primary messenger . The signalling system must be reversible and the protein phosphorylation step of the stimulus-response pathway is reversed through the action of phosphoprotein phosphatases (PPs), which are phosphohydrolases that catalyse the hydrolytic dephosphorylation of proteins ... 

Release of the Primary Messenger. A stimulus such as a wound or di gested meal triggers the release of the signal molecule, also called the primary messenger. 

Draw a generalized molecular circuit based on a signal transduction cascade. Outline the roles of membrane receptors, ligands, primary messengers, second messengers, and protein phosphorylation in the process. 

A number of criteria were defined to establish whether a hormonal effect is mediated through cAMP. First, the concentration of cAMP must rise before hormonal effects become apparent. Second, the response of the target tissue must be proportionate to the amount and the biological activity of the primary messenger. Third, antagonists to a hormone that raises cAMP should reduce the levels of cAMP. Fourth, inhibitors of those enzymes that interfere with cAMP breakdown should enhance the hormonal effect. 

This is the substance which is thought to act as the second messenger of hormone action. The primary messenger is the hormone itself, e.g. ACTH, LH etc, which combines with a specific receptor on the target cell membrane, and this in turn activates adenylate cyclase, the enzyme responsible for the synthesis of cyclic AMP. Cyclic AMP is synthesized in the cell where it modifies the cell s function. 

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