You are studying the responses of cultured intestinal epithelial cells to various types of ionizing radiation. The cells you are using contain a functional p53 gene. Following exposure to ultraviolet light, which of the following events is most likely to occur?

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Quizplus · Accepted Answer

Ultraviolet light can cause DNA damage, leading to activation of the p53 pathway. A functional p53 gene will result in cell cycle arrest, preventing cells from entering S phase to allow for DNA repair.  The protein encoded by p53 is a nuclear localized phosphoprotein. The p53 protein is a transcription factor that regulates the expression of numerous genes involved in suppression of cell growth. Phosphorylation regulates the activity of p53. The level of p53 is low after mitosis but increases during G1. During S phase the protein becomes phosphorylated by the M-phase cyclin-CDK complex of the cell cycle and also by casein kinase II (CKII). One major cell cycle-regulating gene that is a target for p53 is the CDK inhibitory protein (CIP), p21CIP. Activation of p53 results in increased expression of p21CIP with a resultant arrest in the G1 phase of the cell cycle so they cannot begin DNA synthesis in S phase.

You Are Studying the Responses of Cultured Intestinal Epithelial Cells