Chapter 15 Signal Transduction
1) Endocrine, paracrine , autocrine signaling, and cell-cell contact (Fig. 15-2).
Endocrine signaling is long distance signaling. An example would be pancreatic cells secreting insulin. Paracrine signaling is for close proximity. An example would be a nerve cell releasing neurotransmitters. In autocrine signaling the cell that produces the ligand also contains the receptor for that ligand. This is how cancer cells work. In signaling by plasma membrane attached proteins, the target cell does something in response to direct contact from the signaling cell.
2) List examples of 1) steroid hormones and 2) amino acid derivatives that act as ligands.
What are the catecholamines, and which amino acid are they derived from?
Steroid hormones bind cytosolic receptors. They include cortisol, progesterone, estradiol, testosterone, thyroxine and retinoic acid. Steroid receptor complexes increase or decrease the transcription rates of certain genes. Dopamine, norepinephrine, epinephrine, serotonin and histamine are ligands that are derived from amino acids. Catecholamines are ligands derived from the amino acid tyrosine.
3) What's an agonist? What's an antagonist? A doctor prescribes isoproterenol to his patient - why? Why not epinephrine? Another patient receives alprenolol - why? (See page 629 and Fig. 15-5). Agonist= structural analog, antagonist=inhibitor. Isoproterenol has lower Kd (higher affinity) than epinephrine, and will inc. smooth heart muscle contraction. Alprenol is an antagonist (“beta blocker”) and slows heart contractions
4) What are the five kinds of second messengers we described in lecture. (Fig. 15-9 shows only four): cAMP, cGMP, DAG, IP3 and Ca2+
5) What are GTP-binding (switch) proteins? When are they on? When are they off? (Fig 15-8). GEFs help turn them on. GAPs help turn them off. Are “on” when bind GTP, and “off” when bind GDP. Ex: Ras, Ran, trimeric G proteins
6) What are kinases versus phosphatases? Kinases phosphorylate, Phosphatases dephosphorylate
7) What are the main features of a G-protein coupled receptor (GPCR, Figs. 15-10, 15-12, and 15-13)? What is epinephrine and what kinds of receptors does it bind on what cells to induce what responses?
GPCRs= “seven-pass” receptors with amino terminus outside cell and carboxy terminus inside cell. Epinephrine released when glucose needed quickly (inc. glycogenolysis and lipolysis); binds to GPCR receptor , which activates a G protein (switch protein), which activates an effector protein (adenylyl cyclase) producing cAMP NOTE: cAMP does not involve RTK (tyrosine), but uses Ser/Thr kinases! PDE degrades cAMP
8) Describe the three G proteins , , and . Which one binds GTP/GDP (hint for question 6 above).
Gα—binds GDP, is tethered to inner leaflet of plasma membrane, but dissociates from β and γ to activate effector protein (adenylyl cyclase). Gβ and Gγ never separated! Are tethered to inner leaflet and work as a unit.
9) Describe FRET (Fig. 15-14).
10) What is adenylyl cyclase? Figs 15-21 and 15-22. What does it do? How is adenylyl cyclase positively and negatively controlled? Positive: epinephrine binds β adrenergic receptors to activate Gs, actvating adenylyl cyclase; Negative: PGE binds to α adrenergic receptors to activate Gi which then inhibits adenylyl cyclase.
11) The complete "Fight or Flight" road map. YIKES!! What happens when cAMP rises? What happens when cAMP drops?
12) T/F: Second messengers are long-lived in their signaling effectiveness? How is cAMP degraded? PDE
13) What is cAMP-dependent protein kinase and how does it work? (Figs. 15-23 and 16-31)
Do not involve tyrosine kinases (RTK), but use Ser/Thr kinases (binding of cAMP releases catalytic sites…)
14) What do we mean by amplification in signal transduction? Fig. 15-26.
So many steps involved in signal transduction b/c you’re amplifying signal at every step fast...
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