of circular DNA
A simple model of a circularly closed double-stranded DNA in a poor solvent is considered as an
example of a semi-flexible polymer with self-attraction. To find the ground states, the conformational
energy is computed as a sum of the bending and torsional elastic components and the effective self-attraction energy. The model includes a relative orientation or sequence dependence of the effective
attraction forces between different pieces of the polymer chain. Two series of conformations are analysed: a multicovered circle (a toroid) and a multifold two-headed racquet. The results are presented as
a diagram of state. It is suggested that the stability of particular conformations may be controlled by
proper adjustment of the primary structure. Application of the model to other semi-flexible polymers
The diagram of state. The domains where the conformations shown are ground states are painted in different colours.
The bisector (dashed line) marks the case of invariant attraction forces
independent of the monomer sequence. The upper triangle corresponds
to stronger attraction for the toroidal parallel arrangement of a polymer chain.
The lower triangle contains domains where racquets are ground states
because their special geometry provides enhanced attraction. The relative torsional stiffness is fixed c = 1.5.