Question

Cancer biologists have focused on proteins/genes associated with the "restriction point" of the cell cycle to develop the next generation of chemotherapeutics. What is the "restriction point"? Name at least 3 conditions that need to be met for a cell to move beyond the restriction point.

Answer 1

The point at G1 at which commitment occurs and the cell no longer requires growth factors to complete the cell cycle has been termed the restriction (R) point. The R point has been temporally mapped at 2–3 hours prior to the onset of DNA synthesis. The restriction point is defined as a particular time during the cell-division cycle when a particular controlling function or event occurs.

3 conditions that need to be met for a cell to move beyond the restriction point are -

• External influences, such as growth factors, play a large role in carrying the cell past the G₁ checkpoint.
• The cell will only pass the checkpoint if it is an appropriate size and has adequate energy reserves.
• At this point, the cell also checks for DNA damage. A cell that does not meet all the requirements will not progress to the S phase.