Hairpin formation and elongation of biomolecules.

We introduce a model of thermalized conformations in space of RNA-or single stranded DNA-molecules, which includes the possibility of hairpin formation. This model contains the usual secondary structure information, but extends it to the study of one element of the ternary structure, namely the end-to-end distance. The computed force-elongation characteristics are in good agreement with some recent measurements on single stranded DNA molecules.