P-adrenergic signal transduction pathway

Figure 15.4. The p -Adrenergic Receptor Signal-Transduction Pathway. On binding of ligand, the receptor activates a G protein that in turn activates the enzyme adenylate cyclase. Adenylate cyclase generates the second messenger cAMP. The increase in cAMP results in a biochemical response to the initial signal.

Figure 14.8 Epinephrine signaling pathway. The binding of epinephrine to the p-adrenergic receptor initiates the signal-transduction pathway. The process in each step is indicated in black) to the left of each arrow. Steps that have the potential for signal amplification are indicated to the right in green.

After a brief overview of signal transduction, the text describes the structure of the seven-helix transmembrane P-adrenergic receptor and indicates how it transmits to the intracellular side of the plasma membrane a signal arising from binding the hormone epinephrine on the extracellular surface of the cell. The common features of the G proteins are presented next. The description of the information-transmission pathway from hormone stimulus to G proteins to adenylate cyclase is completed by a discussion of how cAMP activates specific protein kinases to modulate the activities of the phosphorylated target proteins. A small number of hormone molecules outside the cell results in an amplified response because each activated enzyme in the triggered cascade forms numerous products. There are many distinct seven-helix transmembrane hormone receptors. 

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