Pictures of the double helix of deoxyribonucleic acid
(DNA) have become so common that everyone is familiar
with its overall shape and structure (Figure 1a).This
structure is known as B-DNA, and represents an average
conformation of DNA, based on fibre diffraction studies.
However, this average shape of DNA is very unlikely to
exist within the cells of living organisms, for several
reasons. First, there is simply not enough room for the
DNA to be stretched out in a perfect, linear B-DNA
conformation