50 Checkpoints in the Cell Cycle

Key Idea: Regulatory checkpoints are built into the cell cycle to ensure that the cell is ready to proceed from one phase to the next. The failure of these systems can lead to cancer.

There are three regulatory points in the cell cycle called checkpoints. At each checkpoint, a set of conditions determines whether or not the cell will continue into the next phase. For example, cell size is important in regulating whether or not the cell can pass through the G1 checkpoint. G2 Checkpoint: Pass this checkpoint if: `Cell is large enough. `Chromosomes have been successfully duplicated.

Checkpoints during the cell cycle

G1 checkpoint

Pass this checkpoint if: `Cell is large enough. `Cell has enough nutrients. `Signals from other cells have been received.

National Cancer Institute

Cancer cell

The cell cycle checkpoints are controlled by enzymes and regulatory proteins. Mutations to genes that encode these enzymes and proteins can lead to cancer. However, many genes are involved so many mutations are needed to develop cancer. p53

One of the most important proteins in the regulation of the cell cycle is the protein produced by the gene p53. Mutations to the p53 gene are found in about 50% of cancers.

1. Explain the importance of cell cycle checkpoints:

Metaphase checkpoint

Pass this checkpoint if: ` All chromosomes are attached to the mitotic spindle.

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The product of the gene BRCA1 has been linked to DNA repair and may be involved in the metaphase checkpoint. Mutations to this gene and another gene called BRCA2 are found in about 10% of all breast cancers and 15% of ovarian cancers.

2. How could the failure of a cell cycle checkpoint lead to cancer?