Consider the Ras signal-transduction pathway. Suppose a mutation occurred in the gene that encodes the transmembrane receptor to which a growth factor binds. The mutation no longer allows the growth factor to bind to the receptor. Which of the following methods could be used to overcome this mutation and allow the pathway to move forward? A. Inject extremely high levels of growth factor into the cell. B. Inject the activated form of Ras into the cell. C. Inject normal levels of nonmutated growth factor into the cell. D. Inject nonmutated tumor-suppressor genes into the cell. E. Inject only the growth factor binding domain of the transmembrane receptor into the cell.

E. Inject only the growth factor binding domain of the transmembrane receptor into the cell.

Explanation:

The reception of signals at the level of target cells requires binding of the signaling molecules to the receptors present on the surface of target cells. Some target cells have intracellular receptors for signaling molecules. Reception of signal is followed by signal transduction and production of response.

Mutation in the gene that encodes the transmembrane receptor for the growth factor would not allow the reception and production of response. Therefore, insertion of a growth factor binding domain of the receptor in the mutated cell would allow the cell to exhibit the normal Ras signal transduction pathway.