Epidermal growth factor promotes cell division. In the absence of this growth factor, is a cell likely to continually go through all the cell cycle phases?

Question

a. yes

b. no

please explain a little bit!

Answer 1

A normal cell would is not permitted to pass to the next cycle if it is not "told" to do so by a growth factor. I don't know how much detail you need, but growth factor receptor transduction pathways, so-called MAPK (mitogen activating protein kinase) pathways culminate in hyperphosphorylation of retinoblastoma protein (Rb) which acts as the main gate keeper to cycle progression. Hyperphosphoyrlated Rb leads to an increase in the G1/S cyclin (Cyclin D) which --and I'm skipping some details -- leads to transition to S phase. Without growth factor signaling, a normal cell is unable to progress through those steps, and thus, remains in G1.