Question

The following events occur when p53 regulates the cell cycle. Place these events in the correct sequence:

1) p53 is activated by posttranslational modifications;
2) The cell cycle is arrested, and apoptosis is initiated;
3) p53 regulates the transcription of multiple target genes;
4) DNA damage causes MDM2 to dissociate from p53.

A. ALL OF THESE
B. 4, 1, 3,2
C. 3, 4, 2, 1
D. 4, 3, 1, 2
E. 2, 1, 4,3

Answer 1

The proper sequence of p53 regulation in the cell cycle starts with CHK2 activating p53, which then leads to the production of p21 to enforce cell cycle arrest, and finally, cell cycle progression resumes if conditions permit.

Step-by-step explanation:

Sequence of p53 Regulation in Cell Cycle

The correct sequence of events when p53 regulates the cell cycle involves several key proteins. Once damaged DNA is detected, p53 acts to halt the cell cycle progression. This stop allows for recruitment of repair mechanisms or, if repair is not possible, triggers apoptosis (cell death).

The CHK2 protein phosphorylates (activates) p53, leading to the production of p21, which further enforces the cell cycle arrest by inhibiting cyclin-dependent kinases (Cdks). Therefore, p53 acts first to sense DNA damage and halt the cycle, then CHK2 activates p53, followed by the production of p21, and only once these events have successfully mitigated the damage does the cell cycle progression resume. Given these roles, the sequence of events is CHK2 (1), p53 (2), p21 (3), cell cycle progression (4).

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