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Nilanjan Bhowmick AIR 3, CSIR NET (Earth Science)
Suryaprakash posted an Question
August 06, 2020 • 22:39 pm
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30 points
30 points
- IIT JAM
- Biotechnology (BT)
Please answer the below question with proper explanation ?
please answer the below question with proper explanation ?
2 Answer(s)
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Anup Padwal
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Answer A G1-S phase. It is also known as DNA damage check point. Single stranded a d double stranded breaks as damage are detected by damage sensory protein(ATR and ATM) which activate CHK 1 and 2. this CHK2 phosphorylate p53 which activate p21. P21 inhibit CDK 2 and cell cycle arrested.
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But I found different answer in book...so what is correct answer?
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But G2M checkpoint is spindle checkpoint.
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No G2M check point is DNA damaged check point
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G1S, S and G2M all are checkpoint of DNA damage.
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Abhijeet Gaurav Best Answer
Answer is C G2 - M The G2-M DNA damage checkpoint is an important cell cycle checkpoint in eukaryotic organisms that ensures that cells don't initiate mitosis until damaged or incompletely replicated DNA is sufficiently repaired. Cells which have a defective G2-M checkpoint, if they enter M phase before repairing their DNA, it leads to apoptosis or death after cell division. The defining biochemical feature of this checkpoint is the activation of M-phase cyclin-CDK complexes, which phosphorylate proteins that promote spindle assembly and bring the cell to metaphase. CyclinB-CDK1 activity is specific to the G2/M checkpoint. Accumulation of cyclin B increases the activity of the cyclin dependent kinase Cdk1 human homolog Cdc2 as cells prepare to enter mitosis. Cdc2 activity is further regulated by phosphorylation/dephosphorylation of its corresponding activators and inhibitors. Through a positive feedback loop, CyclinB-Cdc2 activates the phosphatase Cdc25 which in turn deactivates the CyclinB-Cdc2 inhibitors, Wee1 and Myt1. Cdc25 activates the complex through the removal of phosphates from the active site while Wee1 inactivates the complex through the phosphorylation of tyrosine residues, specifically tyrosine-15.
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Anup Padwal
Answer G1-S is correct when you have to choose only one answer. because all G1-S, S and G2-M checkpoints check for DNA damage. we starts always from G1 phase. If DNA is damaged it is repaired at G1-S checkpoint. Damaged DNA is not replicated i.e. it do not replicate with damage so there is no possibility that DNA enter in G2 phase.