multiple initiation sites.

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NewtoBiology
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multiple initiation sites.

Post by NewtoBiology » Tue Aug 18, 2009 9:17 pm

Hello Biologists,

I have a question inwhich I am stuck on. I am still researching it but I am wondering if you could offer some assistance or information on a web site.

Q: What are the two major reasons fo the multiple initiation sites for eukaryotic replication?

A: REASON #1: I think that there are multiple initiation sites so that synthesis can take place rapidly and at multiple sites. Therefore rather than simply synthesizing one protein, it can synthesis many at one time?

REASON #2: I have no idea.

Thank you for any help or assistance.

Newtobiology

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biohazard
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Post by biohazard » Wed Aug 19, 2009 6:05 am

Hmmh, now I'm not sure if I'm getting this correct, but if the second initiation site is in a different reading frame, you get a whole new protein product from within the same nucleotide sequence. This indeed happens in many prokaryotes, but I cannot recall if eukoaryotes had the same possibility. Anyway, that is the only other reason for multiple initiation sites I managed to come up with at this time.

When you figure out the correct answer, let me know what it was! ;)

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Post by kolean » Thu Aug 20, 2009 2:42 am

You are correct in the reason #1, in that it is a timing issue of getting the whole genome replicated within a reasonable amount of time. And your reason #2 could accurately describe most biological processes :wink: !

But my guess for reason #2 would be for accuracy reasons in replicating the DNA in multiple short strands with the DNA repair and DNA accuracy proofreading complexes could do a proficient job.

I am also coming up with a reason of chromatin modeling lately. As the DNA is being replicated, chromatin modeling proteins, and perhaps several ncRNAs also, are being attached and preparing the chromatin for the rest of the cell cycle. The chromatin modeling proteins prepare the cell to keep its differentiation and thus epigenetic expression, upon replication.

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biohazard
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Post by biohazard » Thu Aug 20, 2009 7:11 am

If the original question was a biology text book question or othrwise related to teaching, I believe the correct answer is probably something fairly straightforward. Of course, the nature usually has dozens of "reasons" for everything, but maybe the two most profound ones are being asked here. Not sure if chromatin modeling or epigenetics fall into this category yet :)

And could you please specify as to how multiple initiation sites actually enhance the accuracy of replication? As far as I know, intitiation sites are realted to gene expression (i.e. the starting point of transcription where data is being copied onto mRNA), whereas replication is started from the origin of replication (i.e. ori) site(s), which is where the proofreading activity is crucial. I must admit I'm bit confused about the original question, as I'm not sure if it means gene expression or DNA replication; the question talks about initiation and replication, and the first answer is about protein synthesis (=gene expression, not replication...)

The question should either be "why there are several origins of replication?" or "why there are several initiation sites of transcription?" OR else I'm completely missing something here :P

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Post by MrMistery » Thu Aug 20, 2009 9:22 pm

i think the question was referring to origins of replication, because in EK cells there are multiple vs only one in bacteria
"As a biologist, I firmly believe that when you're dead, you're dead. Except for what you live behind in history. That's the only afterlife" - J. Craig Venter

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Post by kolean » Fri Aug 21, 2009 3:00 am

I speculated accuracy of replicating the DNA genome in a certain amount of time as another reason, because there is wear and tear on a protein. If you can have multiple replicating enzyme complexes (replisomes) doing just a part of the genome instead of doing the whole genome, then it can get done efficiently and with less errors.

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