Biology 12th Edition

Published by McGraw-Hill Education
ISBN 10: 0-07802-426-9
ISBN 13: 978-0-07802-426-9

Chapter 9 - The Cell Cycle and Cellular Reproduction - Engage - Thinking Scientifically - Page 165: 4


Checkpoints within the cell cycle are advantageous because they help to prevent replication of damaged DNA or cells. In the first checkpoint, the G1 Checkpoint, the cell cycle is stopped if DNA is damaged. If the DNA cannot be repaired, the cell undergoes apoptosis (cell death). In the second checkpoint, the G2 checkpoint, the cell cycle stops if the DNA has not completed replication. Again, if repairs cannot be made, the cell undergoes apoptosis. The final checkpoint occurs during the mitotic stage, arresting the cell cycle if the chromosomes are improperly attached to the mitotic spindle. These checkpoints help to ensure that the cell cycle results in successful production of daughter cells identical to the parent cell.

Work Step by Step

The primary checkpoint is G1 when protein p53, a signaling protein, halts the cycle when DNA damage is detected. If p53 can not repair the DNA, levels increase and lead to apoptosis (cell death). If DNA has not finished replicating by the G2 checkpoint, the start of the M stage is paused until the S stage can be finished. The G2 checkpoint will also halt the cell cycle if the DNA is damaged so that it can repaired. The last checkpoint occurs during the mitotic stage if the chromosomes do not attach properly to the mitotic spindle.
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