Question

Describe the general conditions that must be met at each of the three main cell-cycle checkpoints.

a) DNA replication; Mitotic spindle formation; Cytokinesis
b) Cell size; DNA damage repair; Chromosome attachment to spindle fibers
c) G1 phase entry; DNA synthesis completion; G2 phase entry
d) Chromosome duplication; DNA transcription; Centrosome duplication

Answer 1

The cell cycle includes the G1, G2, and M checkpoints, ensuring proper cell size, complete and undamaged DNA replication, and correct attachment of kinetochores to spindle fibers before cell division proceeds.

Step-by-step explanation:

Cell Cycle Checkpoints

The cell cycle is meticulously controlled by checkpoints to prevent errors during cell division. Three main checkpoints are critical: the G1 checkpoint, the G2 checkpoint, and the M checkpoint (mitotic checkpoint).

• G1 checkpoint: This occurs before the cell enters the S (synthesis) phase. It checks whether the cell is large enough, has enough nutrients, and has undamaged DNA. If conditions are not met, the cell may enter a resting stage called G0 or attempt to repair any issues.
• G2 checkpoint: Before entering mitosis, the cell must ensure all DNA is replicated and not damaged. This checkpoint assesses cell size, protein reserves, and chromosome replication integrity.
• M checkpoint: Occurring near the end of metaphase, the spindle checkpoint ensures each sister chromatid's kinetochore is appropriately attached to spindle fibers. Without proper attachment, anaphase will not proceed, preventing errors in chromosome separation.

These checkpoints are vital for maintaining genetic stability and preventing the propagation of cells with damaged or incomplete DNA.