![]() ![]() Regulates cerebral neurotransmitter release.H 2: increases secretion of gastric acid.Production of aqueous humor fluid in ciliary body.Sphincter muscles of bladder and intestine.Receptor types and their connected G proteins G q proteins : stimulate phospholipase c.G s proteins : stimulate adenylyl cyclase.Function: synthesis of second messengers (see below) depending on which G protein is coupled to the receptor.Activation: by the α subunit of the G protein.GTPase: a small G protein composed of only an α subunit that functions independently to hydrolyze GTP to GDP and phosphate.Three subunits of the G protein dissociate in a complex composed of β and γ subunits and the α subunit.Activated G protein binds GTP instead of GDP.The receptor binds intracellularly to G protein.The binding of an extracellular ligand causes a conformational change in the receptor.γ subunit: complex with the β subunit with a lipid anchor in the cell membrane.β subunit: stable complex with the γ subunit.GTPase activity: hydrolyzes GTP to GDP and phosphate, thereby terminating α subunit activity.Binds GDP in the inactive state and GTP in the active state.A heterotrimeric protein composed of three subunits.Has an intracellular binding site for the G protein.Binding sites for ligands are found in extracellular regions or between helices.Receptor with seven transmembrane helices.Examples of ligands: catecholamines, anterior pituitary hormones ( ACTH, LH, FSH, TSH), glucagon.The action of GPCRs depends on three elements: the receptor, the G protein, and the effector molecule. G protein -coupled receptors ( GPCRs ) are the largest family of membrane receptors. There are three types of cell surface receptors:. ![]() Hydrophilic hormones transmit signals by binding to receptors present in the cell membrane (= cell surface receptors).Ligands of the intracellular receptors ( Progesterone, Estrogen, Testosterone, vitamin D, Cortisol, Aldosterone, Thyroid hormones): PET Da CAT Cell surface receptors Nucleus (e.g., thyroid hormone, vitamin D receptors).Cytosol (e.g., mineralocorticoid, glucocorticoid, estrogen, progesterone, testosterone receptors ).Hormone - receptor complex binds to hormone-responsive elements (specific DNA sequences that are able to bind complementary hormone - receptor complexes) in the nucleus and acts as a transcription factor.A lipophilic hormone diffuses through the cell membrane.Nuclear receptors: ligand-dependent transcription factors that act within the nucleus.IP3- receptor: in the endoplasmic reticulum.Definition : receptors that are located inside the cell.Histamine ( H 1 receptor), angiotensin II, gastrin.Pituitary hormones: oxytocin, ADH ( V 1 receptor).Other hormones: PTH, calcitonin, glucagon, histamine ( H 2 receptor), hCG.Pituitary hormones: TSH, ACTH, FSH, LH, MSH.Hypothalamic hormones: GHRH, CRH, vasopressin ( V 2 receptor).Immunomodulating cytokines: IL-2, IL-6, IFN.Hematopoietic cytokines: G-CSF, EPO, thrombopoietin ( TPO).Nonreceptor tyrosine kinases ( JAK/STAT pathway) Receptor protein serine kinase/ threonine kinases Growth hormones ( IGF-1, FGF, PDGF, EGF).Receptors tyrosine kinas es (MAPK pathway) Catecholamines, acetylcholine, serotonin.Steroid hormones: cortisol, aldosterone, progesterone, estrogen, testosterone.Overview of hormone signal transduction pathways ![]()
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