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2006-11-19 02:45:20 · 3 answers · asked by georgia_gurl345 2 in Science & Mathematics ➔ Biology
Types of DNA
The DNA molecule that Watson and Crick described was in the B form. It is now known that DNA can exist in several other forms. The primary difference between the forms is the direction that the helix spirals.
A, B, C = right-handed helix
Z = left-handed helix (found in vitro under high salt)
B is the major form that is found in the cell. Z-DNA was initially found only under high salt conditions, but the cellular environment is actually a low-salt environment. The question then is whether type Z exist under cellular conditions. Several features have been discovered that can stablize Z-DNA under in a low salt environment.
* Alternating purine/pyrimidine tracts
o poly GC or poly AT stretches
* 5-methyl-cytosine
Because both of these conditions can exists in the cell, it is suggested that stretches of Z-DNA may actually exists in the cell along with other stretches of B-DNA.
In addition to the direction the molecule turns, several other differences exists between the various forms of DNA. The following table summarizes the features of the different forms of DNA.
Form Direction Bases/
360o Turn Helix
Diameter
A Right 11.0 23A
B Right 10.0 19A
C Right 9.3 19A
Z Left 12.0 18A
Copyright © 1998. Phillip McClean
2006-11-19 02:56:36 · answer #1 · answered by Anonymous · 1⤊ 0⤋
There are 3 forms of DNA A B and Z
The most common is the B-form .the well known double helix discovered by Crick and Watson
You find all details in the link
2006-11-19 10:56:05 · answer #2 · answered by maussy 7 · 1⤊ 0⤋
They could be single stranded and double stranded.
Double stranded can be left handed helix or rigt handed helix.
2006-11-19 11:05:17 · answer #3 · answered by chiman 3 · 0⤊ 0⤋