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Supercoiling

supercoiling

(Science: molecular biology) In circular DNA or closed loops of dNA, twisting of the DNA about its own axis changes the number of turns of the double helix.

If twisting is in the opposite direction to the turns of the double helix, i.e. Anticlockwise, the dNA strands will either have to unwind or the whole structure will twist or supercoil termed negative supercoiling.

If twisting is in the same direction as the helix, clockwise, which winds the dNA up more tightly, positive supercoiling is generated. DNA that shows no supercoiling is said to be relaxed

Supercoiling in circular DNA can be detected by electrophoresis because supercoiled dNA migrates faster than relaxed DNA. Circular DNA is commonly negatively supercoiled and the DNA of eukaryotes largely exists as supercoils associated with protein in the nucleosome. The degree of supercoiling can be altered by topoisomerases.


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Need help!!!

... topoisomerase? :? It is an enzyme indeed, but what's the specific function? DNA topisomerase... You may also know it as DNA gyrase... It prevents supercoiling of DNA... http://en.wikipedia.org/wiki/DNA_gyrase

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by Revenged
Fri Mar 30, 2007 10:12 am
 
Forum: Genetics
Topic: Need help!!!
Replies: 6
Views: 947

The Fiber Disease

... fiberglass (some people have compared these threads to fiberglass) in appearance and texture. Struggling to measure the forces of twisting and supercoiling, Mendelson has dragged filaments through gooey fluids, studied time-lapse videos, and measured the folding, bending, and "snap-opening" ...

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by Livvie
Wed Nov 08, 2006 3:01 pm
 
Forum: Human Biology
Topic: The Fiber Disease
Replies: 7403
Views: 748693

DNA replication

... will appear on the wrong strand? In fact, wouldn't there be a lot of them? I realize that it might not be expressed because of histones and supercoiling, but if there are a lot of them, wouldn't some of them, simply by random chance, be expressed? Maybe I'm confused. Pete

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by pdavis68
Tue Aug 22, 2006 7:19 pm
 
Forum: Genetics
Topic: DNA replication
Replies: 1
Views: 601

hyper supercoid band

... is cutting a fragment out of this. Do you purify the plasmid using a gel after extracing it from the cells? You do get different levels of supercoiling of plasmids within bacteria so it may be that the most supercoiled ones can't be cut. Or as you say it may be due to bound proteins.

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by herb386
Fri Jul 14, 2006 10:16 am
 
Forum: Molecular Biology
Topic: hyper supercoid band
Replies: 2
Views: 742

DNA size calibration?

... my hands on some restriction enzyme. Nevertheless your measure maybe accurate, it's simply impossible to be sure. I remember that some plasmids supercoiling were changing with the salinity of the medium, and comparing cultures at different concentration of salt where you could see the different ...

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by canalon
Wed Mar 29, 2006 4:22 am
 
Forum: Molecular Biology
Topic: DNA size calibration?
Replies: 8
Views: 1443
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