DNA plasmid lab

[relamberth]

Hi everyone:
I’m new here so I’m hoping I’m doing this correctly! I am a sophmore at a small private university and am studying cell biology. We just completed a lab on plasmid DNA and ran an agarose gel producing two bands. My professor wants to know why there are two bands of undigested PBR322 (I assume the plasmid?) when the DNA is circular.

I know a few things already:
The smaller the particle the faster it moves through the gel.
Supercoiled DNA moves the fastest so chances are its the lower bar.
We did not cut the DNA so we can not assume size difference.

Could anyone help me figure out what the other piece of DNA could be?
Thanks so much.

[JackBean]

If the smaller band is supercoiled DNA, than the other one will probably be not-supercoiled,don’t you think?

[mith]

flaunting the private university are we?

[relamberth]

Right, I figured that much, but what type of DNA is it? Linear? CIrcular? Has it been nicked? Or do I have any way of knowing?

And I meant nothing with the private univeristy specification. I was pointing out my resources and our labs are terribly limited.

Thanks.

[JackBean]

It’s all circle, just the level of supercoiling differs 😉

[MrMistery]

DNA exists as a mix of topoisomers

[JackBean]

quote MrMistery:

DNA exists as a mix of topoisomers

OK, now you should explain, what are topoisomers 😆

[relamberth]

Well, a topoisomers are varying forms of closed circular dna molecules. So, are you saying (or should i say pointing me to the fact) that the other band of DNA is a topoisomers? Sorry if I sound slow at this…its kind of a first time for me having to explain what I’m doing in lab.

[JackBean]

exactly 😉

As you wrote, the supercoiled DNA will move faster than the relaxed one 😉

[Author]

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