chromosome 2 replication.

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bgyuk
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chromosome 2 replication.

Post by bgyuk » Sat Aug 01, 2009 6:23 pm

Hi i have a query and i cant seem to find the answer anywhere.

As i am sure you all know, chromosome 2 is the the result of a fusion of two chromosomes and it therefore contains 2 centromeres and 4 telomeres. My question is this, durning the chromosome duplication at the start of mitosis how does the area in between the two centromeres get copied, as i was under the impression the cromosome was copied from the telomeres to the centromere.

Thanks for any help.......

Eous
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Post by Eous » Mon Aug 03, 2009 2:23 am

the chromosome duplication is considered the replecation phase of the cell cycle, specifically distinct from the mitosis phase when the cell splits the replicated chromosomes. There is a whole phase inbetween the two (G2). But that's beside the point.

i don't know much specifially about chromosome 2 (for any eukaryote, though it seems you're refering to humans) but...

eukaryotic chromosomes have many origins of replication within the strands. the strands seperate at the origins and so many places along the strand are copied at the same time, which greatly speeds up the process of replicaiton (otherwise it would take relatively forever for a eukaryotic cell, what with there giant repetetive genomes). so a cell would have no problem replicating the area between the centromeres as it should be full of the replication orgins just like the rest of the DNA. And, centromere sections must loosen for replication anyway, so it shouldn't have a problem repicating the whole way throught them onto the other side. Though repication of centromeres has probably been an iffy process, considering that centromeres contain many repeated elements, suggestive of it looping up on itself due to its constrictive centromereic nature (of the code iself or the proteins that associate with it).

but, yeah. that's how i was taught it at least.

bgyuk
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Re: chromosome 2 replication.

Post by bgyuk » Mon Aug 03, 2009 2:42 pm

Thanks for the reply, yeah i was talking about human chromosome two. Yeah after looking into it i had the wrong impression of how the chromosomes are duplicated, so it seems your answer is pretty accurate.

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MrMistery
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Post by MrMistery » Wed Aug 05, 2009 1:26 am

you are actually correct that there would be a problem with having two centromeres though: in metaphase a microtubule from one pole could attach to one centromere and a microtubule from the other pole would attach to the other centromere, so during anaphase in this scenario the chromosome would break. Fortunately for us one of the centromeres is no longer functional, and this doesn't happen.
The telomeres are still there and you can detect the sequence, but that's no problem - it's just repetitive DNA, like we have much of.
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stephenmorphey
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Re: chromosome 2 replication.

Post by stephenmorphey » Fri Aug 21, 2009 6:54 am

Ya you are right, there could definetely be a problem in chromosome2 due to presence of 2 centromeres.
However the inactivity of one of the centromeres in the anaphase acts fortunate for us.
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