Question

What external stimulation is required by mammalian cells to progress through the cell cycle prior to reaching the restriction point?

A: presence of Na+ ions in their culture medium
B: presence of steroid hormones in their culture medium
C: presence of vitamins in their culture medium
D: presence of growth factors in their culture medium

Answer 1

Mammalian cells require the presence of growth factors in their culture medium to pass the restriction point and progress through the cell cycle.

Step-by-step explanation:

The external stimulation required by mammalian cells to progress through the cell cycle, particularly to pass the restriction point, is the presence of growth factors in their culture medium. Cells in the G1 phase of the cell cycle reach a checkpoint where external signals, such as growth factors, are necessary for the cell to proceed with DNA replication in the S phase. These growth factors bind to receptors on the cell's plasma membrane, initiating a cascade of events that lead to the transition into interphase, allowing the cell to progress through the stages of the cell cycle. This is crucial as without these factors, the cells would not receive the required signal to divide and move past the restriction point.