11
$\begingroup$

Is the following correct?

Positive supercoiling = the coiling of DNA helix (B-DNA) on itself during intesified coiling of the two DNA stands in right handed direction

negative supercoiling = the coiling of DNA helix(B-DNA) upon itself during uncoiling of the two DNA strands performed in left handed direction?

I'm a little confused.

Improve this question
$\endgroup$
3
  • $\begingroup$ Think of positive supercoiling as twisting the loop clockwise from the top, while think of negative supercoiling as twisting the loop counterclockwise from the top. $\endgroup$
    – notorious
    Mar 31, 2017 at 21:44
  • $\begingroup$ Positive means left handed or clockwise supercoiling. It results due to overwinding of dsDNA and thus relieve the torsional stress. Whereas the negative supercoil is just the opposite of the earlier. $\endgroup$
    – Ananta
    Jun 9, 2018 at 7:52
  • $\begingroup$ The image from the web book seems to be contradictory with the text and the video. (a) is a left handed helix, so is negative supercoil, (b) is a right handed helix, so is positive supercoil. Cheers $\endgroup$
    – Tuk' Sil'noac
    Oct 9, 2018 at 12:09

1 Answer 1

Reset to default
11
$\begingroup$

According to this powerpoint from the SIU School of Medicine:

Right handed supercoiling = negative supercoiling (underwinding)

Left handed supercoiling = positive supercoiling

And from this Boston University webpage:

If DNA is in the form of a circular molecule, or if the ends are rigidly held so that it forms a loop, then overtwisting or undertwisting leads to the supercoiled state. Supercoiling occurs when the molecule relieves the helical stress by twisting around itself. Overtwisting leads to postive supercoiling, while undertwisting leads to negative supercoiling.

And finally from wikibooks:

Positive and Negative Supercoilings

  1. Positive supercoiling is the right-handed, double helical form of DNA. It is twisted tightly in a right handed direction until the helix creates knot.

  2. Negative supercoiling is the left-handed, double helical form of DNA.

Although the helix is underwound and has low twisting stress, negative supercoil's knot has high twisting stress. Prokaryotes and Eukaryotes usually have negative supercoiled DNA. Negative supercoiling is naturally prevalent because negative supercoiling prepares the molecule for processes that require separation of the DNA strands. For example, negative supercoiling would be advantageous in replication because it is easier to unwind whereas positive supercoiling is more condensed and would make separation difficult.

Topoisomerases unwind helix to do DNA transcription and DNA replication. After the proteins have been made,the DNA template supercoils by the force to make chromatin. RNA polymerase also influence DNA strand to have two different supercoiled directions. The region RNA polymerase has passed forms negative supercoil while the region RNA polymerase that have not passed forms positive supercoil. By these processes, supercoils are generated.

In the following image from web-books:

enter image description here

(a) Positive supercoils (the front segment of a DNA molecule cross over the back segment from left to right). (b) Negative supercoils.

This video, titled "super coil (positive and negative) formation of DNA" should help you visualize this.

Improve this answer
$\endgroup$
2
  • $\begingroup$ @SanjuktaGhosh Does this help clarify it for you at all? $\endgroup$
    – theforestecologist ♦
    Feb 27, 2016 at 16:28
  • 1
    $\begingroup$ I read this topic from a book which cleared my doubts and your answer reassured it.Thank you. $\endgroup$
    – Tyto alba
    Feb 27, 2016 at 20:13

You must log in to answer this question.

Not the answer you're looking for? Browse other questions tagged .