Cytology

1. Mir Abrar

2. Introduction
• cell cycle checkpoints are control mechanisms in the eukaryotic cell cycle which
ensure its proper progression. Each checkpoint serves as a potential termination
point along the cell cycle, during which the conditions of the cell are assessed,
with progression through the various phases of the cell cycle occurring only when
favorable conditions are met. There are many checkpoints in the cell cycle, but
the three major ones are:
 G1 checkpoint allows repair of the damage to take place before the cell enters S phase, where the
damaged DNA would be replicated.
 The S-phase checkpoint provides continual monitoring
of the integrity of DNA to ensure that damaged DNA is
repaired before it is replicated.
 S-phase checkpoint ensures the repair of any errors that
occur during DNA replication, such as the incorporation
of incorrect bases or incomplete replication of segments of DNA.
 G2 prevents the initiation of mitosis until DNA replication is completed.
 This G2 checkpoint senses unreplicated DNA, which generates a signal that leads to cell cycle
arrest.

3. G 1 Checkpoint

4. G 2 Checkpoint

5. Metaphase Checkpoints