Unsustainable DNA molecule when unfolded to be in a line

Numbers that get thrown around for DNA run on the order of magnitude of billions of base pairs. Dimension of a single unit at one nm isn't too bad (ten atoms). That works out to an unraveled length of the order of one to couple meters.
Base units (including the ribose chains) run 25-30 atoms each. 3 x10¹⁰ times three degrees of freedom per atom is a heat capacity of 10¹¹k_B. Bond energies for organic compounds are of the order of four to five hundred kJ/mol. That works out to a maximum chain length of a few hundred atoms before there is sufficient energy stored in two sections of the chain to pull bonds apart if the situation is such that bond strength is the only thing holding the chain together.

 

Not the weight, but the thermal energy in some length of the chain is sufficient to break bonds. Or, the bond is of insufficient strength to play "crack the whip" with the lengths of the chain to either side.

 

And King Kong trying to use it for a jump rope. Perfect analogy.