Select the correct order of events (1-10) for the signal transducon pathway inia

Question

Select the correct order of events (1-10) for the signal transducon pathway iniated by the EGF receptor. (place the number 11 for those which are not applicable).

_____ MEK is phosphorylated by RAF.
____ The receptor undergoes a conformaonal change.
_____ The second messengers IP3 and DAG are produced.

_____ The cytoplasmic tail of the receptor is phosphorylated.

_____ An adaptor protein binds to the phosphotyrosine residues, recruing SOS and Ras.

_____ MEK is phosphorylated by ERK.

_____ RasGAP stimulates GTPase activity of Ras which returns to the GDP bound state.

_____ ERK is phosphorylated by MEK.

_____ The Galpha subunit dissociates from Gbeta/Ggamma.

_____ ERK enters the nucleus and smulates cell proliferaon.

_____ The receptor dimerizes acvang its tyrosine kinase acvity.

_____ The Galpha subunit binds to Phospholipase C.

____ Epidermal growth factor binds to the receptor.

_____ Ras is phosphorylated by RAF.
____ The Galpha protein releases GDP and binds GTP.

____Glucagon binds to the receptor.

Explanation / Answer

1.   Epidermal Growth Factor (EGF) binds to the EGF recptor.

2.   The receptor undergoes a conformational change

3.   The cytoplasmic tail of receptor is phosphorylated

4. (2 and 3 together) The EGF receptor dimerizes (dimerizing arm stretches and binds together) and activates the tyrosine kinase activity.

5.   An Adapter protein (Grb-2) binds to the phophotyrosine residues, further recruiting SOS. SOS then binds to the Ras (a small G protein)

6.   The G alpha protein releases GDP and bind GTP.

7.   Ras GTP stimulates GTPase activity of Ras which returns to the GDP bound stage.

8. MEK is phosphorylated by RAF.

9. ERK is phosphorylated by MEK

10. ERK enters the nucleus and stimulates cell proliferation.

[11. MEK is phosphorylated by ERK

11. The second messengers IP3 and DAG are produced

11. The G alpha subunit dissociates from Gbeta and Ggamma

11. the G alpha subunit binds to phospholipase C.]

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