What are the different forms of DNA

There are four types of DNA basing on the differences in the arrangement of base pairs.

1. B form of DNA :  Most of the cellular DNA shows the structure of B-form of DNA. This type bas 10 base pairs per turn and a wide major groove and narrow minor groove. The diametar of the molecule is 20%A.

2. A form of DNA : This form has 11 pairs per turn and major groove is narrower and much deeper than that of pairs per turn This form DNA exhibits a large tilt of the base
with respect to the helix axis. It has a central hole. This is also right handed helix This form is adapted by RNA-DNA and RNA-RNA helices. The diameter of the molecule in 23 0A.
3. Z form of DNA : Another conformation of DNA is Z-form which contains 12 base pairs per turn and has a zig-zag appearance.
This is left handed helix and this type of structure is formed under high salt concentrations or presence of alternating purine and pyrimidine bases in long DNA molecules. The diameter of the molecule is 18 0A. The significance of Z-form of DNA is not known

4. C form of DNA : This is also right handed form of DNA. But it is having 9.3 bases for each turn or twist. The diameter of the two strands is 19 A.
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