AP BIOLOGY

Detailed explanation-1: -Checkpoints are mechanisms that regulate progression through the cell cycle insuring that each step takes place only once and in the right sequence. Mutations of checkpoint proteins are frequent in all types of cancer as defects in cell cycle control can lead to genetic instability.

Detailed explanation-2: -When one or more components of a cell cycle checkpoint are mutated, the chances of genetic instability during one round of the cell cycle increase accordingly with consequent acceleration of cellular evolution from the normal to the cancerous state.

Detailed explanation-3: -If the cell cycle checkpoints fail, cells that are not replicating correctly will be allowed to continue to grow and multiply. This is dangerous because the cell cycle mutations that are causing the failure can be passed on through the cell lineage.

Detailed explanation-4: -Checkpoint proteins, such as PD-L1 on tumor cells and PD-1 on T cells, help keep immune responses in check. The binding of PD-L1 to PD-1 keeps T cells from killing tumor cells in the body (left panel).

Detailed explanation-5: -Mutations in genes can cause cancer by accelerating cell division rates or inhibiting normal controls on the system, such as cell cycle arrest or programmed cell death. As a mass of cancerous cells grows, it can develop into a tumor.