Axl is a receptor tyrosine kinase that, when the appropriate ligand binds, stimu

Question

Axl is a receptor tyrosine kinase that, when the appropriate ligand binds, stimulates several pathways including the MAP kinase signaling pathway, leading to cell division. You take a cell line and treat it with a ligand that stimulates the Axl-MAP kinase pathway and measure the rate of cell division. You take a second sample of the same cell line, and in addition to adding the ligand, you treat it with a GTPase inhibitor. What do you expect to see with the addition of the GTPase inhibitor?

The rate of cell division will increase, because Ras will not be inactivated.

The rate of cell division will decrease, because Ras will not be activated.

The rate of cell division will decrease, because the ligand cannot bind to Axl.

The rate of cell division will decrease, because autophosphorylation of Axl cannot occur.

The rate of cell division will increase, because more GDP can be exchanged onto Ras.

Explanation / Answer

The correct answer is:

The rate of cell division will increase, because Ras will not be activated

(Without GTP hydrolysis, Ras is continually active and stimulates cellular growth. Mutations that inhibits GTP hydrolysis predispose to cancer, Ras transmits signals from growth factor receptor tyrosine kinase to transcription factor that controls genes required for cellular proliferation).

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