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20 Cards in this Set
- Front
- Back
Receptors
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are proteins that bind to induce biological effects:
-hormones -drugs -paracrine messengers -neurotransmitters |
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Binding properties
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-stereospecific
-saturable -selectivly inhibited -trigger intracellular cascades |
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Cascade targets
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-enzymes
-membrane transporters -ion channels -transcription factors |
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Transcription factors
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retinoic acid,steroids,thyroid hor,vit D:
-diffuse across cell memb. -bind to receptor in cytoplasm or nucleus -complex moves to nucleus -binds to promoters/enchancers -inhibits/stimulates synthesis of proteins |
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Neurotransmitters
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-in PM of cell (excitable)
-fast -channels close until NT binds Na or Ca=channels open=depolerization -K and Cl bind=hyperpolerization i.e. nicotinic AcH=excititory GABA-A=inhibitory |
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G proteins
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-do most hor binding
-stimulate 2nd messengers -integral proteins -7 transmemb glycoprotein family -have 3 subunits: alpha-binds GTP & GDP beta gamma-stays bound to beta |
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cAMP
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-2nd messenger
-Gi receptor - hormone binds to alpha s.u. activates adenylate cyclase=cAMP from ATP |
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Function of cAMP
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prokaryotes-lac operon regulator of transcription
eukaryotes-cAMP binds to regulatory proteins=frees protein kinase A =phosphorylates proteins or goes into nucleus to activate KREB proteins -is degraded by phosphodiesterases (caffeine)=turn cAMP into AMP |
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Adenylate cyclase is stimulated by
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-glucagon
-epinepherine(beta receptors=Gs) -dopamine -PTH -ACTH -MSH -vasopressin -LH,FSH,TSH |
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Adenylate cyclase is inhibited by
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-epinepherine (alpha receptor=Gi)
-dopamine -somatostatin |
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Clinical conditions invloving cAMP
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Pseudohypothyroidism:
abn Gs PTH can't activate adenylate cyclase= -hypocalcemia -mental/neuro probs -PTH levels are norm or inc -toxic nodule Cholera: toxin activates Gs GTP can't be hydrolyzed to turn off cAMP= -inc cAMP prod. -inc H2O/electrolytes -diarrhea Whooping cough: pertusis inactivates Gi= overproduction of cAMP |
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FUnction of phospholipase C
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-Gq
-Phos C cleaves lipids=PIP formed=IP3= binds to Ca ch. & causes release of stored Ca in ER =Ca then binds to:trop C,calmodulin,PKC=exocyt of prods in sec vesicles,muscle cont. -PLC=PIP=IP3=DAG=activtes PKC that in presence of Ca phosphorylates protein side chains |
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Overall effect if cAMP is decreased
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dec in PKA=dec in:
- HR -symp outflow -insulin release |
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Overall effect if IP3 is made
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Ca levels inc:inc in
-vasc sm. musc. cont -exo gland secretion -nasal/bronchial mucus prod,cont of bronchioles -pain |
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Overall effect if cAMP is made
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PKA is made=inc in:
-HR,contractility -vasodilation,bronchdil -H2O permeability in kidney -gastric acid secretion -relaxation of renal sm. musc. |
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How Cyclic GMP is made
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-ANF receptors on cell surface made of guanylate cyclase
-ANF binds=conf change that activates intracellular guan cycl.=changes GTP->cGMP |
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Function of cGMP in retinal rods
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retinal rods:cGMP bound to Na ch.& keeps open till lite present
-lite dec cGMP levels =transducin (Gi) activates phosphodiesterase that cleaves cGMP -ch. close |
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NO & effect on cGMP
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NO activates cytoplasmic guanylate cyclase:
-inc levels of cGMP -PKG is acted on =vasc.sm. musc. relaxation |
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Desensitation and Regulation of Hormone Receptors
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-cAMP ativates PKA=phosphorylation of HR's=they can't bind to Gs=downregulation of receptors
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Downregulation of receptors
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-ligands go to cell
-are endocytosed -vesicles take them up w/ lysosome -ligand is degraded -some go back to cell surface degredation=cause for type II diabetes: -overeating=overexposure of insulin receps to insulin |