Which is the first checkpoint in the cell cycle where a cell can exit if not passed?

Which is the first checkpoint in the cell cycle where a cell can exit if not passed?

• A. G1
• B. G2
• C. M phase
• D. S phase

Answer: (A)

The G1 checkpoint, also known as the restriction point, is the first checkpoint in the cell cycle where a cell decides whether to continue with division or exit into a quiescent state (G0 phase). At this stage, the cell assesses several critical factors such as its size, nutrient availability, DNA integrity, and the presence of growth factors. If these conditions are unfavorable for division, the cell can enter the G0 phase, thus stopping its progression in the cell cycle. This regulation is vital because it ensures that the cell does not proceed with division when conditions are not optimal, which could lead to inadequate growth or the propagation of damaged DNA. In contrast, the other checkpoints occur later in the cell cycle. The G2 checkpoint checks for DNA damage after replication, the M phase checkpoint ensures proper chromosome alignment and spindle attachment during mitosis, and the S phase simply involves DNA synthesis without a specific checkpoint for exiting the cycle. Therefore, the G1 checkpoint serves a crucial role as the first decision point for the cell regarding its division process, making it the correct answer.

The G1 checkpoint, also known as the restriction point, is the first checkpoint in the cell cycle where a cell decides whether to continue with division or exit into a quiescent state (G0 phase). At this stage, the cell assesses several critical factors such as its size, nutrient availability, DNA integrity, and the presence of growth factors. If these conditions are unfavorable for division, the cell can enter the G0 phase, thus stopping its progression in the cell cycle. This regulation is vital because it ensures that the cell does not proceed with division when conditions are not optimal, which could lead to inadequate growth or the propagation of damaged DNA.

In contrast, the other checkpoints occur later in the cell cycle. The G2 checkpoint checks for DNA damage after replication, the M phase checkpoint ensures proper chromosome alignment and spindle attachment during mitosis, and the S phase simply involves DNA synthesis without a specific checkpoint for exiting the cycle. Therefore, the G1 checkpoint serves a crucial role as the first decision point for the cell regarding its division process, making it the correct answer.