[Campbell Biology P.439] Which of the following statements best describes the relationship b... | Practice Question
Which of the following statements best describes the relationship between the cell cycle-stimulating pathway Figure 18.24 and the cell cycle-inhibiting pathway Figure 18.25 in the context of cancer development?
A: Both pathways promote cell division, but mutations in the stimulating pathway lead to less control, while mutations in the inhibiting pathway lead to more control.
B: The stimulating pathway involves proto-oncogenes whose activation promotes cell division, while the inhibiting pathway involves tumor-suppressor genes whose inactivation prevents cell division.
C: Cancer typically arises from loss-of-function mutations in the stimulating pathway and gain-of-function mutations in the inhibiting pathway.
D: Cancer can result from gain-of-function mutations in proto-oncogenes within the stimulating pathway or loss-of-function mutations in tumor-suppressor genes within the inhibiting pathway.
E: The stimulating pathway only controls normal growth, and the inhibiting pathway only responds to DNA damage, neither directly causing cancer.
Explanation
Cancer development often involves malfunctions in both cell cycle regulation pathways. The stimulating pathway, involving proto-oncogenes like Ras, can lead to cancer through gain-of-function mutations that cause excessive cell proliferation. Conversely, the inhibiting pathway, involving tumor-suppressor genes like p53, can lead to cancer through loss-of-function mutations that remove the brakes on cell division. Both types of mutations disrupt normal cell cycle control, leading to uncontrolled growth.