Consider the Ras signal-transduction pathway. Suppose a mutation occurred in the
ID: 100655 • Letter: C
Question
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?
Inject extremely high levels of growth factor into the cell.
Inject the activated form of Ras into the cell.
Inject normal levels of nonmutated growth factor into the cell.
Inject nonmutated tumor-suppressor genes into the cell.
Inject only the growth factor binding domain of the transmembrane receptor into the cell.
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.
Explanation / Answer
Answer:- Option E
Explanation:-RAS is a guanine nucleotide-binding protein. RAS is activated in response to the binding of extracellular signals, such as growth factors. The extracellular ligands such as growth factors bind to the transmembrane receptor. This in turn activates RAS. The inactive form of RAS guanosine diphosphate (RAS-GDP) is converted to active RAS guanosine triphosphate (RAS-GTP).
In mentioned question, mutation of gene for the receptor doesn’t allow growth factor to bind to the receptor. Here the availability of growth factor is there in the system, but receptor is mutated and hence binding is not possible. Therefore injecting growth factor will not cause the binding to the receptor.
Therefore, option (A) and (C) are not correct answers.
The inability of binding of growth factor to receptor stops the RAS signal transduction pathway, thus stopping the growth. This is the action desired when tumor suppression (excess growth suppression is needed) Thus, tumor suppressor genes will not overcome the block by the mentioned mutation.
Therefore, option D is not correct answer.
The activated RAS ie RAS GTP is needed for the pathway to continue. However injecting activated RAS will trigger the further pathway only for some time. It will not allow the cell to produce activated RAS on its own.
Therefore option (B) is not correct.
The transmembrane receptor because of mutation cannot bind to the growth factor. The mutation therefore has caused changes in the growth factor bindng domain of the receptor.
Injecting growth factor binding domain will allow the binding of growth factor and thus the pathway can function normally.
Thus correct answer is option E.
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