BIOL 151 Review Session 9 18 25 7pm Mahar Auditorium This diagram shows an oscillating pathway at 4 successive time points The signal is constantly present but gene expression caused by TFa oscillates between on and o In this pathway TFa activates a gene encoding a phosphatase that targets TK2 Problem 1 5 Which of the following are true of this pathway 1 At time point 1 the TFa gene is on but at time point 4 the TFa gene is off 2 At time point 3 the phosphatase gene is being expressed but at time point 4 the phosphatase gene is off 3 At time point 2 the TK2 kinase is inactive but the TK1 protein is active 4 At time point 3 ubiquitin dependent proteolysis of the phosphatase protein is occurring but the expression of the phosphatase gene has stopped 5 At time point 4 the TK1 gene is on but the TK2 and TFa genes are off Problem 6 9 You analyze a different cell and nd the following about the signaling pathway Signal is binding to the receptor and has been for some time TK1 is phosphorylated TK2 and TFa are not phosphorylated What else would be true of this cell 6 The receptor would be phosphorylated 7 TFa would be in the cytoplasm 8 TK1 would be undergoing protein turnover but TK2 and TFa would not 9 This could be an oscillating pathway if expression of phosphatase gene targeting TK2 is caused by TFa Problem 10 14 For each of the following determine whether the signaling pathway would be A Functional and TFa causes changes in gene expression when signal binds the receptor B Permanent and TFa continues to affect gene expression even if the signal is washed away C Temporary and TFa driven gene expression to go on and off when the signal was constantly present D Nonfunctional where gene expression would not change when the signal is binding to the receptor Always assume Protein Turnover is happening 10 If TK1 activated TK2 a phosphatase that targets TFa 11 If TFa activated a gene that encodes a Phosphatase that targets TK1 12 If TK2 activated TFa and a Kinase that targets TK1 13 If the receptor activated both TK1 and TK2 Problem 15 24 Which of the following are true about the EGF pathway 15 When EGF binds to the EGF receptor the receptor subunits dimerize and phosphorylate each other 16 Phosphorylation of the cytoplasmic domain of the receptor blocks signaling activity 17 GRB2 and SOS the Ras GEF only bind to the receptor when the receptor is phosphorylated 18 When the Ras GEF is active Ras is bound to GTP 19 Blocking the function of the Ras GEF could lead to over activation of the pathway 20 Blocking the function of the Ras GAP could lead to over activation of the pathway 21 For Raf to be activated it must touch Ras that is bound to GTP 22 If you block the GTPase activity of Ras it would block the EGF pathway 23 If MEK is phosphorylated Ras is most likely binding to GTP 24 If you block the RBD Ras Binding Domains of Raf it would cause Raf to be phosphorylated and activated Bonus Question 1 Which of the following could cause the EGF pathway to continue to signal with ERK in the nucleus even of the EGF signal was washed away and lost Don t forget protein turnover is happening in cells 1 If EGFR activated a kinase that targeted Raf 2 If ERK targeted and activated NF1 the Ras GAP 3 If MEK targeted and activated SOS the Ras GEF 4 If ERK activated a gene that encoded a kinase that targets Ras 5 If ERK activated a gene that blocked the Ubiquitination of SOS the Ras GEF Bonus Question 2 The G12C mutation in Ras blocks the Ras GTPase funciton Which of the follow is true about the EGF pathway in cells with the G12C Ras mutation 1 The full EGF pathway would be activated even if no EGF signal was ever present 2 The EGF pathway could be blocked by increasing the activity of NF1 the Ras GAP in the cell 3 After the EGF signal bound to the receptor the EGF pathway would continue to signal even if the EGF receptor was later removed by receptor mediated endocytosis in degradation mode 4 Raf would continue to actively phosphorylate MEK even if the initial EGF signal was washed away 5 MEK and ERK would never get phosphorylated because Raf would not be able to make contact with Ras