The relay protein Ras is part of the EGF pathway that promotes cell division (see Figure 9.10). The active form of Ras has GTP bound to it, whereas the inactive form has GDP. GTP is hydrolyzed to GDP and Pi to switch Ras from the active to the inactive form. Researchers have discovered that certain forms of cancer involve mutations in the gene that encodes the Ras protein. Which of the following types of mutations would you expect to promote cell division and thereby lead to cancer?
a) a mutation that prevents the synthesis of Ras
b) a mutation that causes Ras to bind GDP more tightly
c) a mutation that prevents the GTP bound to Ras from being hydrolyzed
d) a mutation that prevents Ras from binding to Raf
e) both b and c
Answer: C
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