What is the primary function of tumor suppressor genes? a. stop all cells from dividing b. stop certain cells from dividing c. help oncogenes produce oncoproteins d. allow the cell to skip certain phases of the cell cycle
The Correct Answer and Explanation is:
Correct Answer: b. stop certain cells from dividing
Explanation:
Tumor suppressor genes are crucial components in the regulation of the cell cycle and play a significant role in preventing uncontrolled cell growth. Their primary function is to stop certain cells from dividing, especially when conditions are not favorable for cell division. This includes cells with DNA damage, cells that have reached the end of their useful life, or cells that are dividing too rapidly. By halting the cell cycle, tumor suppressor genes allow time for DNA repair or initiate programmed cell death (apoptosis) if the damage is irreparable.
One of the best-known tumor suppressor genes is TP53, which encodes the p53 protein. Often called the “guardian of the genome,” p53 responds to cellular stress by stopping the cell cycle at the G1/S checkpoint. If DNA damage is detected, p53 allows time for repair mechanisms to fix the errors. If the damage cannot be repaired, it promotes apoptosis to eliminate the defective cell, preventing it from becoming cancerous.
Another example is the RB1 gene, which produces the retinoblastoma protein (Rb). Rb controls progression through the cell cycle by inhibiting transcription factors needed for DNA replication. Only when a cell receives appropriate growth signals does Rb become inactivated, allowing the cell cycle to proceed.
If tumor suppressor genes are mutated or inactivated, the control mechanisms they provide are lost. This can lead to unregulated cell division, one of the hallmarks of cancer. Unlike oncogenes, which promote cell division when mutated, tumor suppressor genes must be inactivated (usually both alleles) to contribute to tumor formation. This is known as the “two-hit hypothesis.”
In summary, tumor suppressor genes do not stop all cells from dividing but selectively prevent certain cells from proliferating when division would be harmful, making them essential for maintaining normal cell growth and preventing cancer.
