Question

can someone explain how they calculated twist T=-60 for 940 turns?

U L LUIC llave superhelix densities of about 0.06. To get an idea of what this means, consider a hypothetical DNA mol- ecule of 10,500 bp, which is in the solution B form, with 10.5 bp/turn. Then L, is 10,500 bp/(10.5 bp/turn), or 1000 turns. Each DNA strand crosses the other 1000 times in the relaxed circle. If the topoisomerase DNA gyrase (see page 1055) twisted the molecule to a superhelical density of -0.06, then L = -0.06 Lo, or L = -60. This change could be accommodated, for example, by the helix axis writhing about itself 60 times in a left-handed sense, which would correspond to AW = -60, T = 0; the molecule would have 60 left-handed superhelical turns. Alternatively, the twist of the molecule could change so that it had 940 turns in 10,000 bp (T = 940) or ange so that .cd superhelicspond to Am

Answer 1

Answer:

( Linking number (4K): an integer representing the number of times one estrand of DNA would have to be passed through the other strand in order to separate the two stands entirely. The linking number (24) describe the & lopology of the ANA molemle. Linking number is sum of twist numbe (Twl & arithing number (wr) ul. Lx=Twtwr one strand The Number of helical turn of of DNA about the other. Tw=y To go for right-handed helix +5 SS Right handed helix. Left handed helix. Wo Torsional stress of a DNA molecule in which DNA douce holix crosses over itself in three dimensional space.

Wr=4 At fully relaxed condition the number of linking number of circular clored ONA is represented as eko arreper colled on the actual link ich number would not be Lk The difference, betwear actual linking number (2k) & Lko in designated der Alk. 1. . ALK & LK- LKs Super helikal density is defined as the change of linking number (Au) aith. to eto it is expressed as 6 = – 0.01 in dicates than 1% of helical turns Present in DNA have been removed. ghe change of linking norber (Alk) ( will be sum of the change of twent number (AW) & cwrith number (wer) ALK - ATA AWr)

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