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Scott_Handout3-key - MCB 104 Handout#3 1 The Ras pathway is...

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2/15/2010 MCB 104; Handout #3 1. The Ras pathway is the canonical Receptor Tyrosine Kinase (RTK) signaling pathway. Put the following steps of Ras signaling in order (note: we’ll very likely be talking about the Ras pathway again in the genetics section of the course): [5] GRB2 recruits Sos, a protein with GEF activity [3] EGFR proteins autophosphorylate tyrosine residues on their intracellular domains [2] EGFR proteins dimerize [4] GRB2, an adapter protein is recruited to the activated intracellular domain of EGFR [6] Sos mediates the exchange of Ras-GDP Ras-GTP [1] Ligand binds to extraceullar domain of EGFR (a.k.a. HER2), an RTK [9] MEK phosphorylates MAPK, MAPK phosphorylates downstream targets [8] Phosphorylated Raf phosphorylates MEK, which activates MEK. [7] Ras mediates the phosphorylation of Raf, activating Raf 2. How can one molecule of ligand binding to one receptor molecule be amplified to result in a robust downstream response? Think of specific examples of amplification in GPCR and RTK signaling. Multiple targets can be activated at each step in the pathway. e.g. one activated GPCR can activate multiple adenylyl cyclases, each of which produces multiple cAMPs, each of which activates a kinase that activates multiple downstream targets. e.g. one activated EGFR dimer activates multiple Ras molecules, each of which activates multiple MAPKs, each of which activates multiple downstream targets. 3. Actin is polar. Which end (barbed or pointed) grows faster? Which end depolymerizes faster? Which end is ADP-bound? Describe an experiment that demonstrates that actin filament nucleation is the rate-limiting step in the actin cycle (-) = pointed = ADP-bound = depolymerizes faster (+) = barbed = ATP-bound = polymerizes more efficiently ATP-bound G-actin is incorporated into the filament, generally at the (+) end. Gradually, the ATP gets hydrolyzed. So expect more ATP-actin at the (+) end, and more ADP-actin at the (-) end.
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