Thankyou... but what am i asking is different. My question is how do we get to know the standard torsional angles for loops to know the possible torsional angle rotations for alpha, beta and other 5 torsional angles of a nucleic acid structure loop.
For e.g. Check this "http://www.fli-leibniz.de/ImgLibDoc/nana/IMAGE_NANA.html" where average torsional angle of a nucleic acid structure helices is given