The tumor suppressor gene p 53 induces cell cycle arrest at –
**Core Concept**
The p53 tumor suppressor gene plays a crucial role in maintaining genomic stability by regulating cell cycle progression, DNA repair, and apoptosis. It acts as a "guardian of the genome" by preventing the propagation of cells with damaged DNA.
**Why the Correct Answer is Right**
p53 induces cell cycle arrest at the G1 phase, allowing cells to repair DNA damage or undergo apoptosis if the damage is irreparable. This is mediated by the activation of p21, a cyclin-dependent kinase inhibitor that inhibits the activity of cyclin-dependent kinases (CDKs) and prevents the transition from G1 to S phase. The p53-p21 pathway is a critical mechanism for preventing the propagation of cells with damaged DNA.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because p53 does not induce cell cycle arrest at the G2 phase, where cells are preparing for mitosis.
**Option B:** This option is incorrect because p53 does not induce cell cycle arrest at the S phase, where DNA synthesis occurs.
**Option C:** This option is incorrect because p53 does not induce cell cycle arrest at the M phase, where cells undergo mitosis.
**Clinical Pearl / High-Yield Fact**
It's essential to remember that p53 mutations are associated with a high risk of developing various types of cancer, including breast, lung, colon, and brain tumors. The p53 gene is often referred to as the "cancer gene" due to its critical role in preventing tumor formation.
**Correct Answer:** G1. p53 induces cell cycle arrest at the G1 phase.