Question

The p53 protein is a transcription factor that regulates a cell's progression through the cell cycle after DNA is damaged by ultraviolet ( UV ) radiation. The p53 pathway is shown in Figure 1.
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Please note: p53 regulating image is for the entire problem, whereas part C image is only for part C.

(a) A skin cell completes one round of the cell cycle. Describe the products.
(b) Based on Figure 1, explain how p53 regulates the cell cycle in the presence of damaged DNA .
(c) Draw an X on the template in the space provided for your response to indicate the phase during which the replication of damaged DNA would occur.
(d) Based on Figure 1, explain how a mutation to p53 may lead to an increased risk of cancer.

Answer 1

Answer:

(a) Since skin cells undergo the process of mitosis, the product of one cell cycle is 2 identical daughter cells.

(b) The levels of p53 protein in the cell will rise in response to DNA damage. This will stop the cycle at one point to give time to the repair machinery to regain stability. As can be seen in the figure, CDK inhibitors have been produced which are responsible for halting the cell cycle.

(c) The S phase (synthesis phase) is when replication of damaged DNA would occur.

(d) p53 responds in one of 3 ways to an event of DNA damage: arresting the cell-cycle, apoptosis (programmed cell death), or repairing the DNA. If there has been a mutation in p53, neither of the three way would take place to prevent more copies of damaged DNA being made. A mutated p53 protein would no longer be able to suppress tumors.

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