生物學-II-2.ppt

Second messengers C-amp (IP3) Switch proteins The proteins that bind to second messengers function as switch proteins switch proteins go on to regulate the activity of numerous other proteins in the cell Receptors act as transcription factors Type I ligands: Steroids (testosterone, estrogen, cortisol, etc.) 111 2222 bind to their receptors in the cytosol the receptor dissociates from its heat shock proteins and becomes activated. Type II ligands vitamin D, thyroid hormones, and retinoids. bind to their receptors in the nucleus. Brassinosteroids (plants lacked steroid hormones) plant steroid receptor is a cell surface receptor (transmembrane protein called a leucine-rich repeat receptor). Steroid receptors act as transcription factors Hormone response element (HRE) steroid signal Cell surface receptors can interact with G proteins All water-soluble mammalian hormones bind to cell surface receptors. signal-transducing, GTP-binding regulatory proteins called heterotrimeric G proteins. The receptor proteins consist of seven-transmembrane a helices Schematic drawing of two types of seven-spanning receptors. G-protein-1 G-protein-2 G-protein-Ca Heterotrimeric G proteins cycle between active and inactive forms α subunit has a GTPase activity Activation of adenylyl cyclase increases the level of cyclic AMP Nearly all the effects of cAMP in animal cells are mediated by the enzyme protein kinase A (PKA). PKA phosphorylates a transcription factor called CREB (cyclic AMP response element–binding protein). CREB binds to the cAMP response element (CRE), which is located in the promoter regions of genes that are regulated by cAMP. The Arabidopsis genome encodes 20 putative members of a cyclic nucleotide-gated channel family. Pollen tube growth in lily has been shown to be stimulated by concentrations of cAMP as low as 10 nM (Tezukaet al. 1993). cAMP activates K+ channels in the plasma membrane of fava bean (V. faba) mesophyll cells. 再看一次 Signal Transduction in Prokaryote