many human cells can be stimulated to divide by hormonelike growth factors that bind to receptor proteins (R) on the plasma membrane and trigger an internal signal-transduction cascade. In many cases, however, the process of contact inhibition prevents mitosis when cells are in direct contact with one another. Contact inhibition occurs when proteins called cell adhesion molecules (CAMs) interact, causing them to change shape so that the growth-factor signaling proteins that normally associate with CAMs are replaced by another protein, called M. Both pathways are depicted in the figures.
Which of the following statements accurately uses the information presented to support the hypothesis that interruption of M function in a single body cell can result in cancer?
A. Protein 3 will be prevented from interacting with CAMs, causing the cell cycle to stop permanently.
B. The ras protein will remain bound to DNA, blocking expression of genes required for mitosis.
C. Growth-factor signaling can trigger mitosis in cells that are in direct contact with other cells.
D. The receptor proteins of body cells will no longer bind to growth-factor proteins.