  The conformational behavior of a giant DNA mediated by condensing agents in
the bulk solution has been investigated through experimental and theoretical
approaches. Experimentally, a pronounced conformational hysteresis is observed
for folding and unfolding processes, by increasing and decreasing the
concentration of condensing agent PEG (Polyethylene glycol), respectively. To
elucidate the observed hysteresis, a semiflexible chain model is studied by
using Monte Carlo simulations for the coil-globule transition. In the
simulations, the hysteresis loop emerges for stiff enough chains, indicating
distinct pathways for folding and unfolding processes. Also, our results show
that globular state is thermodynamically more stable than coiled state in the
hysteresis loop. Our findings suggest that increasing chain stiffness may
reduce the chain conformations relevant to the folding pathway, which impedes
the folding process.
