DNA Types A, B & Z

[neo007]

Can anyone tell me where the A-form and Z-form of DNA is found? I understand that the B form is found in normal human cells, but where do the other two come from and do/can they exist in human cells?

[chadn]

The A-form of DNA exists under conditions of dehydration or high-salt concentrations.

 

The Z-form I believe exists only in the lab. In addition to these three there are also C, D, E, and P forms. All of these....if I am correct are found under laboratory conditions, only. I could be wrong about this, however.

[neo007]

so, the B form could potentially "denature" into the A form under high salt concentrations or with dehydration?

[chadn]

B-DNA doesnt need to denature to form A-DNA.

[Yggdrasil]

The A form of DNA is biologically relevant because it is the conformation taken by double stranded RNAs and DNA-RNA hybrids. Furthermore, some bacteria can convert their DNA from B-DNA to A-DNA when they form spores (Mohr, SC. et al. (1991) PNAS 88, 77-81). Supposedly, the DNA is more resistant to degradation in the A conformation than in the B conformation.

 

Z-DNA is primarily though to be an artifact of the laboratory and there is no evidence that it is biologically relevant.

[neo007]

Are there any sites with info about A and Z form DNA in detail? I've tried searching on google, but can't seem to find anything

[Yggdrasil]

Wikipedia has some basic information on A and Z DNA (http://en.wikipedia.org/wiki/DNA#A_and_Z_helices_formation), while you can find the crystal structures of A & Z DNA on the PDB (http://www.rcsb.org/pdb/static.do?p=education_discussion/molecule_of_the_month/pdb23_3.html)

[neo007]

i've come across the wikipedia one before, and yeah is rather basic, but the second link seems more useful and more to what i'm looking for

thanks!