how we could know practically if the dna is single stranded or double stranded?

Question

anonymous · Answer

Francis Crick and James Watson put forward the model of DNA's structure, according to Rosalind Franklion's evperiment, which is the DNA's X-ray diffraction .The result of the diffraction showed that there are two kinds of structure that would show up repeatedly. One show up every 0.34 nm, which is the distance between the nearby base pair.And another show up every 3.4 nm, which is the distance of every turn. Based on the result, Francis Crick and James Watson inferred  the  structure of DNA.(which is double stranded and spiral )