The tumor suppressor gene p53 induces cell cycle arrest at:
**Core Concept**
The tumor suppressor gene p53 plays a crucial role in maintaining genomic stability by regulating the cell cycle in response to DNA damage. p53 induces cell cycle arrest to allow for DNA repair or apoptosis in damaged cells, thereby preventing the propagation of mutations that can lead to cancer.
**Why the Correct Answer is Right**
When DNA damage is detected, p53 is activated and binds to specific DNA sequences, leading to the transcription of target genes involved in cell cycle arrest. The most critical target gene induced by p53 is p21 (cyclin-dependent kinase inhibitor 1), which inhibits the activity of cyclin-dependent kinases (CDKs), thereby blocking the progression of cells through the G1 phase of the cell cycle. This allows for DNA repair or apoptosis to occur, preventing the propagation of mutations.
**Why Each Wrong Option is Incorrect**
* **Option A:** This option is incorrect because p53 does not induce cell cycle arrest at the G2-M phase checkpoint.
* **Option B:** This option is incorrect because p53 is not primarily involved in inducing cell cycle arrest at the S phase checkpoint.
* **Option D:** This option is incorrect because p53 does not induce cell cycle arrest at the G0 phase checkpoint, which is typically associated with quiescent cells.
**Clinical Pearl / High-Yield Fact**
p53 mutations are found in approximately 50% of human cancers, highlighting the critical role of this tumor suppressor gene in preventing carcinogenesis.
**Correct Answer:** G1. Cell cycle arrest at the G1 phase is induced by p53 through the transcription of target genes involved in cell cycle regulation.