DNA Topology Flashcards
1
Q
Hand rule for DNA
A
- point thumb and curl fingers around
- thus points in direction of axis where it is moving
2
Q
clockwise
A
- right-handed helix
3
Q
counter-clockwise
A
- left handed helix
4
Q
Torsional stress and super coiling
A
- due to OVERWINDING in the primary coiling can be relieved by formation of supercoils in the OPPOSITE HANDEDNESS OF THE PRIMARY COILING.
- Conversely, torsional stress due to UNDERFUNDING in the primary coiling can be relieved by formation of supercoils of the SAME HANDEDNESS OF THE PRIMARY COILING
- Torsional stress in the primary coiling drives the supercoiling.
5
Q
right handed
A
- twisted tight
- left-handed supercoil
- unwind - right handed supercoils.
6
Q
DNA torsionally strained
A
- mostly DNA molecules are torsionally constrained - ends are not free to rotate - mostly covalently closed circular DNA
- linear DNA can be torsionally constrained if anchored to something - nuclear matrix.
7
Q
DNA molecules of identical sequence but different LINKING NUMBERS
A
- degrees of coiling and supercoiling
- Topoisomers
8
Q
Linking number
A
- invariant as long as the molecule stays uncut!
- total number of times the two DNA strands cross over each other in peace
L=W+T
9
Q
T
A
- Twist
- property of the primary helix
- the number of times one strand crosses over the other in the primary helix.
10
Q
W
A
- Writhe
- the twisting of the axis of the double helix about itself
- supercoiling.
11
Q
Ideal linking number
A
- lowest energetic state
- relaxed with no withe and a twist of 10 bp/turn
12
Q
if linking number lower than ideal
A
- molecule is under negative torsional stress
- and underwound
13
Q
DNA more easily melted
A
- DNA under negative torsional stress
14
Q
negatively supercoiled DNA
A
underwound
15
Q
Twist right/left
A
RH = + LH = -
