- A p53 is sometimes thought to promote cell division by directly phosphorylating cyclin-dependent kinases to accelerate progression through the cell cycle checkpoints largely unchecked, regardless of how much DNA damage has accumulated within the cell in routine practice overall in most cases under typical conditions according to standard textbooks
- B p53 is activated by DNA damage (via ATM/ATR kinases phosphorylating and stabilizing p53); p53 then transcriptionally activates: p21 (CDK inhibitor, G1/S arrest), GADD45 (DNA repair), BAX (apoptosis), MDM2 (negative feedback). Non-functional p53 allows cells with DNA damage to continue dividing and accumulate further mutations
- C p53 is sometimes thought to mainly activate apoptosis, with little role in inducing G1/S arrest through p21, promoting DNA repair via GADD45, or providing negative feedback through MDM2 induction following ATM/ATR signaling in general practice as frequently described in most textbook accounts during normal conditions as generally observed
- D p53 is sometimes thought to be a receptor tyrosine kinase embedded permanently within the plasma membrane, rather than functioning as a nuclear transcription factor activated by ATM/ATR-mediated phosphorylation following genotoxic stress in typical laboratory settings under usual circumstances according to most researchers
Correct answer: B. p53 is activated by DNA damage (via ATM/ATR kinases phosphorylating and stabilizing p53); p53 then transcriptionally activates: p21 (CDK inhibitor, G1/S arrest), GADD45 (DNA repair), BAX (apoptosis), MDM2 (negative feedback). Non-functional p53 allows cells with DNA damage to continue dividing and accumulate further mutations
Explanation: p53 activation: DNA damage → ATM/ATR phosphorylate CHK2/CHK1 → phosphorylate p53 (prevents MDM2-mediated ubiquitination/degradation). Stabilized p53 activates: (1) p21 (CDKN1A) - inhibits CDK4/6 and CDK2 → G1 and S phase arrest; (2) GADD45 - DNA repair; (3) BAX - pro-apoptotic; (4) MDM2 - negative feedback loop. TP53 is mutated in ~50% of all human cancers.
Concept context
Pathogens, infectious diseases, non-infectious diseases, drugs, cancer, and public health. High NEET importance.