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. Author manuscript; available in PMC: 2009 Apr 9.
Published in final edited form as: Nat Rev Microbiol. 2008 Feb;6(2):111–120. doi: 10.1038/nrmicro1836

Figure 2. Mammalian signalling through membrane Receptors.

Figure 2

a | Membrane receptor kinases dimerize and autophosphorylate a tyrosine or threonine residue upon binding to a hormone. They then initiate a phosphorelay signalling cascade in the cell. These cascades can include the mitogen-activated protein kinase (MAPK), Akt and Jun amino-terminal-kinase (JNK) pathways, and often lead to DNA synthesis and cell proliferation. b | G-protein-coupled receptors (GPCRs) are receptors that are coupled to guanine-binding proteins (G proteins) when they are inactive. G proteins consist of an α-, a β- and a γ-subunit. If a GPCR binds its signal (such as adrenaline or noradrenaline (NA)), the α-subunit of the G protein is uncoupled and exerts its effect. Different families of the α-subunit associate with different effectors and exert different effects. The αi inhibits adenylate cyclase and diminishes the levels of intracellular cyclic AMP (cAMP), the αs activates adenylate cyclase to increase the levels of cAMP and the αqactivates phospholipase C (PLC).