Unlocking the Secrets of Cell Cycle: Checkpoints and Their Purpose
What are the checkpoints in the cell cycle and what is their purpose?
A) G1 checkpoint - ensures DNA replication;
B) G2 checkpoint - monitors chromosome attachment;
C) S checkpoint - evaluates DNA synthesis;
D) M checkpoint - examines spindle fiber attachment.
Answer:
The purpose of checkpoints in the cell cycle is to ensure proper sequence and safety in cell division, which includes the G1 checkpoint for size and DNA integrity, the S checkpoint for DNA replication accuracy, the G2 checkpoint for chromosome duplication and energy reserves, and the M checkpoint for proper spindle attachment.
Explanation:
The cell cycle is monitored by critical regulatory points known as checkpoints. These checkpoints help to maintain the proper sequence of events and ensure cell division is carried out correctly and safely. The purpose of these checkpoints is to verify whether the conditions are right for the cell to proceed to the next phase of the cell cycle.
G1 checkpoint: Occurs just before entry into S phase, ensuring the cell is large enough and has the necessary resources for DNA replication. It also checks the integrity of the DNA to ensure there is no damage.
S checkpoint: Determines if the DNA has been replicated properly. This checkpoint prevents the progression to the next phase of the cell cycle if the DNA replication is incomplete or if errors are detected.
G2 checkpoint: Bars entry into mitosis. It assesses if all chromosomes have been fully and accurately duplicated and if the cell has sufficient energy reserves and proteins. It also checks for any DNA damage and attempts to repair it if detected.
M checkpoint: Also known as the spindle checkpoint, it occurs near the end of the metaphase stage and ensures that every kinetochore on the chromosomes is attached to spindle fibers from opposite poles. This is crucial for the accurate segregation of sister chromatids during anaphase.