The lab you work in has discovered a previously unidentified extracellular signal molecule called QGF, a 75,000 -dalton protein.You add purified QGF to different types of cells to determine its effect on these cells.When you add QGF to heart muscle cells, you observe an increase in cell contraction.When you add it to fibroblasts, they undergo cell division.When you add it to nerve cells, they die.When you add it to glial cells, you do not see any effect on cell division or survival.Given these observations, which of the following statements is most likely to be TRUE?

Question

Quizplus · Accepted Answer

The different responses observed in heart muscle cells, fibroblasts, and nerve cells suggest that QGF activates different intracellular signaling pathways in these cells. This implies that the cells have different receptors for QGF or different downstream effectors that are activated by the same receptor. Option A is not necessarily true and there could be other mechanisms by which QGF acts on cells. Option B is unlikely because glial cells were not affected and it is possible that they have a different receptor or downstream effectors for QGF. Option D is unlikely because the different responses in different cell types suggest that they have different receptors or downstream effectors for QGF.

The Lab You Work in Has Discovered a Previously Unidentified