2. The following is a description of a signaling pathway initiated by receptor tyrosine kinases. Ligand → RTK → Sos → Ras → Raf → MEK → ERK → Transcription factor → Cell growth A. (3pts) Which of these steps indicates the protein is activated after a GTP exchange step? B. (3pts) Which of these proteins can be deactivated by phosphatases? C. (4pts) Describe a mutation that would cause Ras to be permanently "on"? Would this mutation lead to high or low levels of cell growth? D. (4pts) Describe a second mutation in a different protein (i.e. not Ras) that can reverse the effect of the mutation in Part B on the level of cell growth E. (4pts) Why are mutations in pathways like this commonly found in cancers? 2. The following is a description of a signaling pathway initiated by receptor tyrosine kinases. Ligand → RTK → Sos → Ras → Raf → MEK → ERK → Transcription factor → Cell growth A. (3pts) Which of these steps indicates the protein is activated after a GTP exchange step? B. (3pts) Which of these proteins can be deactivated by phosphatases? C. (4pts) Describe a mutation that would cause Ras to be permanently "on"? Would this mutation lead to high or low levels of cell growth? D. (4pts) Describe a second mutation in a different protein (i.e. not Ras) that can reverse the effect of the mutation in Part B on the level of cell growth E. (4pts) Why are mutations in pathways like this commonly found in cancers?
GDP/GTP exchange is where A. Ras-GDP proteins are activated after the activation of TRK. They are able to bind and regulate many effectors proteins in such an active form. After a GTP exchange step B, GDP to GTP is activated, which leads to the next step, which is to relay the signal downstream. The phosphatases can be turned on or off by the protein Ras. Since it is inactivated by phosphatases and GAPS, it is only activated for a short time. H or K or N Ras are caused by a single base substitution. This causes the GTP to always get activated to relay the signal downstream, which causes the Rasprotein to be permenantly on by attaching to it. It will increase the cell growth so much that it will lead to cancer. transduction of signals in this pathway is required for a cell to decide whether to grow or produce new cells. Cells can be produced in an orderly manner through the controlled pathway. The unruly type of cell division which leads to cancer is caused if there is a change in the proteins involved.
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