When will DNA adopt an A-form helix?

[whamola411]

Can DNA adopt an A-form helix, and can RNA adopt a B-form helix. If so, under what conditions, and if not, why not?



The only idea I have so far is that low humidity will help form the A form, and high humidity forms the B form. However, can humidity change in our bodies? I'm lost here.

 

[Ygggdrasil]

As you mentioned, DNA can adopt either an A-form helix or B-form helix, although in aqueous solution, the B-form is most prevalent. As you noted, DNA can be artificially made to adopt an A-form helix under conditions where it is dehydrated. Naked DNA in the body would not adopt an A-form helix because there will always be water around. However, researchers have seen that DNA can adopt an A-form like geometry when bound by certain proteins, such as some DNA polymerases. Furthermore, certain bacteria that form spores will dehydrate themselves and with the help of specific DNA binding proteins, convert their DNA to adopt an A-form geometry.

RNA is capable of existing only in an A-form helix. The 2' hydroxyl in RNA prevents the sugar from adopting the C2'-endo conformation required for a B-form helix.

 

[whamola411]

Thank you so much, I couldn't find information on this anywhere!