This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Pathology
What is the half-life of p53 protein in normal cells? 
Select and explain. 
A. 20 minutes, B. 60 minutes, C. 12 hours, D. 1 day
A: 20 minutes
Answer: A: 20 minutes 
Explanation: In non stressed, healthy cells, p53 has a sho half-life (20 minutes), because of its association with MDM2, a protein that targets it for destruction. When the cell is stressed, for example by an assault on its DNA, p53 undergoes post-transcriptional modifications that release it from MDM2 and increase its half-life. Unshackled from MDM2, p53 also becomes activated as a transcription factor. Ref: Robbins 8th edition Chapter 7.