Gene expression in G2 ? Upregulated because 4n?

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Julie5
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Gene expression in G2 ? Upregulated because 4n?

Post by Julie5 » Mon Nov 29, 2010 6:07 pm

I hope the experts here will forgive me, but are genes expressed in G2? I am sure I have read somewhere in passing that cells can be functional in G2 (ie, as well as G1/G0) so I would think that must mean genes are expressed, and, since S has doubled the number of chromosomes (ie, 4n - briefly tetraploid), does that mean all gene expression in G2 (assuming it happens!) is also upregulated????

Really sorry (and v. embarrased!) if this is a daft question!

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JackBean
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Post by JackBean » Tue Nov 30, 2010 9:20 am

Sure some genes are expressed. The G(ap) phases are so called because when using the very first microscopes, one was able to distinguish only the synthesis of new chromosomes and cell division, so these two phases between seemed like empty, being asleep, but nowadays we know, there is a lot going on.

However, I'm not sure about the level of transcription, but I think it's pretty similar, because the cell regulates level of enzymes and other proteins it needs. However, some proteins needed to equip the DNA may be upregulated ;)
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magicsiew
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Post by magicsiew » Tue Nov 30, 2010 3:35 pm

Genes are expressed in G1,S and G2, throughout the cell cycle. In G1, the genes expressed are used for RNA and protein synthesis, which as a preparation for further process. While in S phase, genes the expressed are required for DNA replication. In G2,again the genes expressed are for RNA and protein synthesis.

In S phase, the chromosome number is mixture of 2n-4n, in G2 only is 4n. This is because replication occur in S phase, and many regulation checkpoint have to pass to ensure the chromosome are replicated completely, therefore, it is a mixture, rather than just 4n.

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Post by magicsiew » Tue Nov 30, 2010 3:41 pm

I dont really understand why you say the genes are upregulated for 4n? If the chromosome number do not reach 4n, it wont pass through the S phase checkpoint (under normal condition) and the cell cycle will arrested at S phase only.

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JackBean
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Post by JackBean » Wed Dec 01, 2010 11:05 am

because usually you have 2 copies of gene to be transcribed, while in G2 you have 4 copies of that gene, so you could have two-times higher speed of transcription ;)
http://www.biolib.cz/en/main/

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Julie5
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Post by Julie5 » Wed Dec 01, 2010 5:36 pm

Thank you both so much! I get a bit nervous asking questions here in case they are the really dumb ones!!!

It's a lot clearer in my head now, so many thanks.

magicsiew, yes, I didn't mean to imply that each gene was upregulated, but that, as Jack says, overall expression was upregulated simply because there are now four copies, thanks to S phase replication, of each gene.

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