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DNA (structure:The DNA helix: (DNA can adopt different conformations (Z…
DNA
structure:The DNA helix:
DNA can adopt different conformations
Structure of B-DNA
1. major and minor grooves
right-handed
helixRise (distance between stacked bases)
Pitch (distance to complete one turn)
10 bps per turn
5.B-DNA Z-DNA play a role in the control of transcription
A-DNA
more tightly wound than B-DNA, and has minor grooves of similar width
right handed
Z-DNA
righted handed
Zigzagged form
forming Z-DNA frequently occur near the start of genes
DNA can be supercoiled
Topology:
Dealing with structural properties that are unchanged by continuous deformations
Topological property of a DNA molecules:
unaffected by deformations of DNA strands as long as no breaks
Linking number:
= the number of times that one DNA strand winds in the right-handed direction around the helix axis when the axis is constrained
Twist number:
A measure of the helical winding of the DNA strands around each other
Writhing number:
a measure of the coiling of the axis of the double helix
L = T + W
△W = - △T
Biological Functions of supercoiling
more compact shape
unwind and thereby affect the interactions between DNA and other molecules
hinder or favor
Continuous deformations of DNA
The sugar-phosphate backbone is conformationally constrained
RNA
