Hi Laura,
Thanks for your interest in 3DNA and for posting on the forum.
I understand what you mean, but I do not think 3DNA (or other tools I know of) can provide you with a straight answer. It all depends -- what specifically is your definition of "an extended conformation", i.e., "single strands without helical configurations"? If you have a starting model,
mutate_bases and
analyze/rebuild/frame_mol in 3DNA may help.
As always, I am willing to extend 3DNA in ways that make sense to me and are useful to the community. Currently, 3-dimensional nucleic acid structure modeling is one aspect I am interested in.
Xiang-Jun