Li-Fraumeni syndrome (LFS1) is a rare hereditary disorder that leads to a predisposition to cancer. This hereditary disorder is linked to mutations in the tumor suppressor gene encoding the transcription factor p53. p53 acts at the G1 checkpoint. If damaged DNA is detected, p53 halts the cell cycle. As p53 levels rise, the production of p21 is triggered. p21 enforces the halt in the cell cycle. A variant of Li-Fraumeni, called LFS2, is thought to occur due to a mutation of the CHK2 gene, which is also a tumor suppressor gene. CHK2 regulates the action of p53. Which of the following cascades is most likely to occur in a normal cell that does not contain the LFS mutation?

CHK2, p53, p21, cell cycle progression.

Explanation:

In a normal cell with no LFS mutation, during the G1 stage of cell cycle progression, the CHK2 activates if there is damage in the DNA. CHK2 activates p53, which is a tumor suppressor protein that will hold the cell cycle in G1/S until the DNA is repaired. The p53 protein activates p21, a protein that binds to CDK2 and stops the cell cycle. The cell cycle will continue once the damage is repaired.      

when a reversible reaction is occurring in both directions at the same rate; the products and reactants do not change in concentration. a chemical reaction where the compound is broken into its constituent parts.

explanation:

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organ system-an organ system is a group of organs that work together to perform one or more functions. each does a particular job in the body, and is made up of certain tissues.