[Campbell Biology P.297] The "MAKE CONNECTIONS" box states that PDGF signals cells by bindin... | Practice Question

The "MAKE CONNECTIONS" box states that PDGF signals cells by binding to a cell-surface receptor tyrosine kinase, and asks how the results would differ if a chemical blocked phosphorylation. Considering the information from Figure 12.18 about the effect of PDGF, what would be the most likely outcome if phosphorylation were blocked in the experimental setup?

  • A: Both cells with and without PDGF would proliferate, as phosphorylation is not critical for cell division.
  • B: Cells with PDGF would fail to proliferate, similar to the "Without PDGF" control, because the signal transduction pathway would be interrupted.
  • C: Cells without PDGF would begin to proliferate due to an alternative signaling pathway being activated.
  • D: Cell division would be unaffected, as PDGF acts directly on the nucleus.

Explanation

The "MAKE CONNECTIONS" box states that PDGF signals through a receptor tyrosine kinase, which typically involves phosphorylation as a key step in activating downstream signaling pathways. Figure 12.18 shows that without PDGF, cells fail to divide. If phosphorylation were blocked, the signal from PDGF binding to its receptor would not be effectively transduced inside the cell, mimicking the absence of PDGF. Therefore, cells with PDGF would fail to proliferate, just like the control group without PDGF.