{[ promptMessage ]}

Bookmark it

{[ promptMessage ]}

MCB9b - Topological Linking Number(Lk Tw ist(Tw Writhe Wr...

Info icon This preview shows pages 1–8. Sign up to view the full content.

View Full Document Right Arrow Icon
Topological Linking Number (Lk): Twist (Tw) + Writhe (Wr) Tw = “the number of times Watson strand crosses Crick” helical repeats in B-form DNA are rig ht-handed, considered + direction Wr = “the number of times WC duplex crosses WC duplex” compaction of B-form DNA against itself, also termed supercoiling + supercoils = right handed like B-form DNA; - supercoils = opposite direction Lk = 6 Tw = 6 Wr = 0 Lk o = most favorable Lk = B-form DNA with no supercoils
Image of page 1

Info icon This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document Right Arrow Icon
Twist and writhe can interconvert, but Lk CANNOT change without cleavage of a phosphodiester bond. DNA in cells is has an Lk less than Lk o like the picture above.
Image of page 2
negative supercoil positive supercoil Tw = 6 Wr = 0 Tw = 6 Wr = -1 +1 Lk = 6 no enzyme is required Tw = 6 Wr = -1 Lk = 5 enzyme is required! Lk = 6 must remove + supercoils nucleosome DNA packaging and DNA replication require changes in DNA topology “topoisomers” differ in Lk; Lk is altered by “topoisomerase” enzymes
Image of page 3

Info icon This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document Right Arrow Icon
Changes Lk in steps of 2. Enzyme breaks one duplex and passes another duplex through the break.
Image of page 4
Image of page 5

Info icon This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document Right Arrow Icon
Image of page 6
Image of page 7

Info icon This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document Right Arrow Icon
Image of page 8
This is the end of the preview. Sign up to access the rest of the document.

{[ snackBarMessage ]}

What students are saying

  • Left Quote Icon

    As a current student on this bumpy collegiate pathway, I stumbled upon Course Hero, where I can find study resources for nearly all my courses, get online help from tutors 24/7, and even share my old projects, papers, and lecture notes with other students.

    Student Picture

    Kiran Temple University Fox School of Business ‘17, Course Hero Intern

  • Left Quote Icon

    I cannot even describe how much Course Hero helped me this summer. It’s truly become something I can always rely on and help me. In the end, I was not only able to survive summer classes, but I was able to thrive thanks to Course Hero.

    Student Picture

    Dana University of Pennsylvania ‘17, Course Hero Intern

  • Left Quote Icon

    The ability to access any university’s resources through Course Hero proved invaluable in my case. I was behind on Tulane coursework and actually used UCLA’s materials to help me move forward and get everything together on time.

    Student Picture

    Jill Tulane University ‘16, Course Hero Intern