Second messengers guanosine 5 diphosphate

The most common second messenger activated by protein/peptide hormones and catecholamines is cyclic adenosine monophosphate (cAMP). The pathway by which cAMP is formed and alters cellular function is illustrated in Figure 10.1. The process begins when the hormone binds to its receptor. These receptors are quite large and span the plasma membrane. On the cytoplasmic surface of the membrane, the receptor is associated with a G protein that serves as the transducer molecule. In other words, the G protein acts as an intermediary between the receptor and the second messengers that will alter cellular activity. These proteins are referred to as G proteins because they bind with guanosine nucleotides. In an unstimulated cell, the inactive G protein binds guanosine diphosphate (GDP). When the hormone... 

There are several intracellular second messengers that are activated by metabotropic receptors, also referred to as G protein-coupled receptors (Duman and Nestler 1999). These receptors couple with G proteins that are heterotrimers made up of a-, (3- and y-subunits. Interaction of the G protein heterotrimer with activated receptor increases the exchange of guanosine triphosphate (GTP) for bound guanosine diphosphate (GDP), resulting in dissociation of the heterotrimer into free a and (3y subunits that in turn can regulate second messen-... 

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