How does the p53 tumor-suppressor protein control cell-cycle checkpoints?

Verified step by step guidance

1. Understand that the p53 protein is a tumor suppressor that plays a critical role in maintaining genomic stability by regulating the cell cycle.
2. Recognize that p53 functions primarily by acting as a transcription factor that can activate or repress the expression of genes involved in cell cycle arrest, DNA repair, and apoptosis.
3. Identify that when DNA damage or cellular stress is detected, p53 becomes stabilized and accumulates in the nucleus, where it can induce the expression of the gene encoding p21, a cyclin-dependent kinase inhibitor.
4. Know that p21 inhibits cyclin-CDK complexes, which are essential for progression through the G1/S checkpoint, thereby causing cell cycle arrest and allowing time for DNA repair.
5. Realize that if the damage is irreparable, p53 can also initiate programmed cell death (apoptosis) to prevent the propagation of damaged cells, thus controlling cell-cycle checkpoints and preventing tumor development.

Key Concepts

p53 Tumor-Suppressor Protein

p53 is a crucial protein that acts as a tumor suppressor by regulating the cell cycle and preventing the proliferation of damaged cells. It functions mainly as a transcription factor that can activate genes involved in DNA repair, cell cycle arrest, or apoptosis in response to cellular stress or DNA damage.

Cell-Cycle Checkpoints

Cell-cycle checkpoints are control mechanisms that ensure the proper progression of the cell cycle by verifying whether processes like DNA replication and chromosome segregation have been accurately completed. These checkpoints prevent the division of cells with damaged DNA, maintaining genomic stability.

Mechanism of p53-Mediated Cell-Cycle Arrest

Upon DNA damage, p53 is stabilized and activates the transcription of genes such as p21, which inhibits cyclin-dependent kinases (CDKs). This inhibition halts the cell cycle at the G1/S checkpoint, allowing time for DNA repair or triggering apoptosis if the damage is irreparable.