When Ras is activated, cells will divide. A dominant-negative form of Ras clings too tightly to GDP. You introduce a dominant-negative form of Ras into cells that also have a normal version of Ras. Which of the following statements is true?

Question

(a) The cells you create will divide less frequently than normal cells in response to the extracellular signals that typically activate Ras.
(b) The cells you create will run out of the GTP necessary to activate Ras.
(c) The cells you create will divide more frequently compared to normal cells in response to the extracellular signals that typically activate Ras.
(d) The normal Ras in the cells you create will not be able to bind GDP because the dominant-negative Ras binds to GDP too tightly.

Answer 1

(a) Dominant-negative Ras is considered "dominant" because it prevents normal Ras from doing itsjob. This mutant protein, when overexpressed in a cell, binds to—and essentially monopolizes—other signaling partners in the pathway, but it cannot activate the target proteins that lie downstream. In this way, dominant-negative Ras mutants block Ras signaling and inhibit cell proliferation. The creation of GTP in the cell is independent of Ras and its associated signaling pathways [choice (b)]. An activated Ras mutant will cause cells to divide more frequently. In this situation, the Ras pathway does not work and cells should not divide more frequently [choice (c)]. The binding of GDP to dominant-negative Ras should not affect the ability of normal Ras to bind GDP, as the concentration of GTP in the cell is quite high, and the normal Ras is inactive and bound to the GDP it created from GTP the last time it was active.