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Home Q & A Board Biology-Related Homework Help Cell Biology
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nurse2be14 nurse2be14
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11 years ago
correct, detailed answers are much appreciated:)
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irinairina
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11 years ago
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11 years ago
It is regulated by checkpoints. So if a cell does not pass a checkpoint it is sent into G0.. In g1 you have the synthesis of macromolecules in S phase that is DNA replication and G2 is additional growth.
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11 years ago
It has a variety of checkpoints.

One checks DNA in G1 to check for any damage. This is mediated by ATM, which phosphorylates Chk2. This phosphorylates cdc25, which is exported out of the nucleus so it cannot remove the phosphate from the Tyr15, so the cell doesn't replicate its DNA in S phase until the DNA is free of errors.

Another one checks the DNA after it has been copied in S-phase for errors. If it has one ATR phosphorylates p51. This acts a transcription factor for the P21 gene which makes p21 (a protein) , that prevents cdk activation so the cell doesn't go into mitosis until the DNA is repaired.

Finally mad2 checks to make sure all the chromosomes are properly attached to microtubules. If it doesn't it prevents APC from separating them at the metaphase plate and moving into opposite poles.
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