Question

Drosopholia eye development is an example of cell differentiation directed by signal binding to a receptor tyrosine kinase (RTK). In this pathway, R7 photoreceptor development requires a receptor (SEV, sevenless), which is activated by binding to a plasma membrane bound signal (BOSS, bride-of-sevenless) displayed on the adjacent R8 cell Receptor activation leads to activation of RAS via two proteins, Drk (down- stream of receptor kinases) and Sos (son-of-sevenless). Activated RAS leads to activation of a phosphorylation cascade that activates the specific transcription factors necessary for photoreceptor differentiation Question 15 (1 point) How does the membrane bound signal BOSS activate the RTK leading to the activation of the signaling pathway? O RTK binding to BOSS causes a conformational change in the receptor tyrosine kinase that activates Ras's GTPase activity, allowing for signal propagation O RTK binding to BOSS causes a conformational change in the receptor tyrosine kinase activating its kinase activity, which phosphorylates Ras and activates the signaling pathway ORTK binding to BOSS causes receptor dimerization and cross-phosphorylation and subsequent activation of the signaling pathway RTK binding to BOSS causes a conformational change in the receptor tyrosine kinase activating its kinase activity, which phosphorylates Drk and activates the signaling pathway Question 16 (1 point) The receptor to Ras activation pathway involves two proteins. Drk and Sos. What roles do these two proteins play in the activation of RAST Receptor activation of Sos leads to activation of Drk which can bind to Adenate Cycle and activate it leading to the production of CAMP Cyclic AMP can then bind to and activate Ras O Drk is an adaptor protein that can link sos to the activated receptor. Sosta GTPase Activating Protein GAP that activates RAS by stimulating its GTPase activity Activated Dik can phosphorylate Sos activating itsase activity. Sos is a Ras- kinase and can activate Ras via phosphorylation O Ork is an adaptor protein that can find sos to the activated receptor Sasha Guarine Nucleotide Exchange Factor (GEF) that activates RAS by cousing it to GDPGTP

Answer 1

15. RTK binding to BOSS cause receptor dimerization and cross phosphorylation and subsequent activation of signalling pathway.

16. Drk is an adaptor protein that can link Sos to the activated receptor. So is a Guanine Nucleotides exchange factor that activate RAS by causing it to release GDP and bind to GTP.

17. With a hyperactive GTPase domain, RAS would hydrolyze GTP to GDP very rapidly. This would block its ability to activate downstream effector proteins hence R7 cell would not develop.