In a circular DNA molecule of 126 bp with 10.5 bp/turn, which of the following represents an unstrained circle? (L = linking number, T = twist and W = writhe)
A)L = 12, T = 12, W = 0
B)L = 11, T = 11, W = 0
C)L = 11, T = 12, W = -1
D)L = 12, T = 11, W = +1
E)L = 11, T = 10, W = 0

Question

Quizplus · Accepted Answer

BIn a circular DNA molecule, the linking number (L) is the sum of the twist (T) and writhe (W). For an unstrained circle, W = 0, so L = T. Given 126 bp and 10.5 bp/turn, the DNA makes 126 / 10.5 = 12 turns. Thus, options where L = T = 12 or L = T = 11 without writhe (W = 0) represent unstrained circles.

In a Circular DNA Molecule of 126 Bp with 10