Simple DNA question

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amolvaidya06
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Simple DNA question

Post by amolvaidya06 » Thu Apr 12, 2007 8:46 am

Is the double-helix considered to be two molecules of DNA or one molecule? Basically, is each strand a separate polymer of DNA, or is it looked at as one polymer together.

If it's one polymer together, what happens in interphase when the double-helix is separated in order to replicate?

Darby
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Post by Darby » Thu Apr 12, 2007 3:29 pm

It's one molecule, and even during replication, it's never one lone strand, as the strands separate and get replicated like unzipping a zipper and building new zippers from/for each side as you unzip.

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Post by wbla3335 » Thu Apr 12, 2007 6:46 pm

Depends on if you ask a chemist or a biologist. There's no covalent bonding between strands, only hydrogen bonding, which chemically doesn't contribute to defining a molecule. Biologists, though, routinely call a double helix a molecule. No blood has yet been drawn over this issue, but there is no universal agreement.

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alcyon
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Post by alcyon » Sun Apr 15, 2007 12:32 pm

but since the 'shape' of an DNA molecule is described as a 'double helix', then i think when we talk about a DNA molecule we'd be talking about both strands.

The modle in which DNA separates into two single strands the replicate is only a rough model to show the relationship between the original DNA and the latter ones. As far as we know, thing don't happen like that in real life.

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kotoreru
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Post by kotoreru » Sun Apr 15, 2007 4:47 pm

Yes, presumably the double helix would never separate into the two discrete strands under any natural circumstances.

Am I right in saying that during the denaturing phase i.e. the heating part of the PCR (sorry about my ignorance of the terminology), the two strands of any given 'molecule' of DNA will separate completely?

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alcyon
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Post by alcyon » Sun Apr 15, 2007 5:10 pm

@kotoreru: yes i think you're right in saying that, becasue the molecules of DNA in the PCR process is usually only a cut-out (or restricted) part of the original much-longer DNA, and they do separate at some stage into separate strands (but not always, i think it can be done via similar process of the actual replication taking place inside a living organism?) during this process.

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