If RB mutants cannot bind to E2F, what is the likely outcome for cell division?

• A. Cell division will be arrested
• B. Cell division will occur normally
• C. Cell division will be accelerated
• D. Cell division will be delayed

Answer: (B)

The outcome of RB mutants that cannot bind to E2F is that cell division will likely be accelerated. In normal cell cycle regulation, the RB protein plays a critical role in controlling the transition from the G1 phase to the S phase of the cell cycle. RB functions by binding to E2F transcription factors, thereby inhibiting their activity and preventing the expression of genes required for S phase entry and cell division.

When RB cannot bind to E2F due to mutations, E2F is free to promote the transcription of these genes, which leads to the progression of the cell cycle without the usual regulatory checks that prevent uncontrolled division. This loss of control can result in unregulated cell proliferation, which is often observed in cancerous cells. Thus, the inability of RB to bind E2F leads to an increased likelihood of cell division occurring at a faster rate than normal, contributing to accelerated cell division in the context of RB mutants.