GTPases serve in many signal transduction pathways and the presence of GTP or GDP dictates where the pathway is on or off, respectively. Which of the following statements is true regarding guanine nucleotide exchange factors (GEF) and the role in these signaling pathways?

a. They hydrolyze GTP into GDP and Pi.

b. They decrease the GTPase activity of the G-protein.

c. They catalyze the dissociation of GDP on the G-protein and promote the replacement of GTP.

d. none of the above

None of the above.

Explanation:

GTPases are the regulatory proteins that are involved in the signal transduction pathway involving the activation of the G protein. The mutation in these proteins cal lead to cancer cells.

The guanine nucleotide exchange factors (GEF) allows the replacement of GDP by GTP. They activates the GTPase activity of the cell and can also activate the multiple GTPase activity of the cell. The Ras superfamily is activated by the GEF.

Thus, the correct answer is option (d).