Diagram (just use arrows in the same way you diagrammed in a former test a stimulus leading to the activation of PKC, for example) in as much detail as possible what happens to a mammalian cell when it is irradiated, leading to when the cycle stops due to DNA damage. Include and name the famous mammalian checkpoint protein known by its molecular weight, as well as name another protein it activates. This other protein's function can be described by a 3 letter acronym that contains the letter K. Mention the acronym.
Comprehensive question
When a mammalian cell is irradiated, DNA damage occurs and the tumor protein 53 (p53) and MDM2 get phosphorylated and MDM2 does not bind with p53. Normally, in a cell lacking DNA damage, p53 is highly unstable and its concentration does not increase. This is because the protein MDM2 binds with p53 and marks it for ubiquitin-mediated degradation.
Because p53 is not degraded, its concentration builds up and this leads to cell cycle arrest and halts progression at the G1 phase. p53 binds with DNA and stimulates a gene to produce the protein p21, which then interacts with the cell division stimulating proteins (cdk2, cdk3, cdk4, and cdk6).
In the cell with DNA damage, cdk4 and cdk6 phosphorylate the retinoblastoma tumor-suppressing protein Rb which is an important protein to get into the S-phase in the cell cycle. The protein p53 also stops the cell cycle from going into the S-phase by decreasing the expression of cyclin a (cdk2).
Once the cell cycle is halted, the cell tries to repair itself. In the case of extensive DNA damage and the repair of the DNA is not possible, the p53 either permanently arrests the cell cycle or triggers apoptosis by directly activating the transcription of the apoptosis genes.
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