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TLS Online TPP Program

#Question id: 1260

Which of the following statement regarding RTK/Ras pathway is incorrect?

#Unit 4. Cell Communication and Cell Signaling

  1. Receptor activation leads to re-localization of Sos from the cytosol to the membrane, which brings Sos close to its substrate, Ras∙GDP, which is already bound to the plasma membrane by means of a covalently attached lipid.

  2. Binding of Sos to Ras∙GDP leads to conformational changes in the switch I and switch II segments of Ras, thereby opening the binding pocket for GDP so it can diffuse out.

  3. The SH2 domains in GRB2 selectively bind to proline-rich sequences in Sos; different SH3 domains in other proteins bind to proline-rich sequences distinct from those in Sos.

  4. Ras is activated by the exchange of GDP for GTP. Active Ras∙GTP binds to the N-terminal regulatory domain of Raf, a serine/threonine kinase, thereby activating its kinase activity.

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TLS Online TPP Program

#Question id: 1237

#Unit 4. Cell Communication and Cell Signaling

Arrange the following events in the proper order in which they occur during transduction of the Notch/Delta signaling pathway:

a. cleavage of Notch by TACE                                  

b. binding of Delta to Notch

c. translocation of Notch segment to the nucleus      

d. interaction of Notch with transcription factors     

e. cleavage of Notch by Presenilin 1  
TLS Online TPP Program

#Question id: 1238

#Unit 4. Cell Communication and Cell Signaling

Which of the following can lead to loss-of-heterozygosity in a tumor-suppressor gene?

a. deletion of the normal copy                       

b. non dysjunction during mitosis

c. somatic mutation of the normal copy

d. mitotic recombination between a wild-type and mutant allele
TLS Online TPP Program

#Question id: 1239

#Unit 4. Cell Communication and Cell Signaling

GTPases serve in many signal transduction pathways and the presence of GTP or GDP dictates whether the pathway is on or off, respectively. Which of the following statements is TRUE regarding guanine nucleotide exchange factors (GEF) and the role in these signaling pathways?
TLS Online TPP Program

#Question id: 1240

#Unit 4. Cell Communication and Cell Signaling

Pull-down assays using proteins that ONLY bind to the GTP-bound version of the small G-protein can be used to detect when small G proteins like Rac1 have been activated by various growth factors.  You were given two lysates, one having been treated with platelet-derived growth factor (PDGF) and the other not treated with PDGF. This method is similar to performing co-IPs, so based on that knowledge, which of the following steps is erroneous?
TLS Online TPP Program

#Question id: 1241

#Unit 4. Cell Communication and Cell Signaling

Which of the following is a common step in the opening/closing of ion channels by acetylcholine and rhodopsin binding to their receptors?
TLS Online TPP Program

#Question id: 1242

#Unit 4. Cell Communication and Cell Signaling

Rhodopsin, a light-sensitive GPCR whose role in vision is dependent on its phosphorylation status, is influenced in part by the protein arrestin.  Which of the following is TRUE with regard to rhodopsin and vision?