  Non-coding RNA sequences play a great role in controlling a number of
cellular functions, thus raising the need to understand their complex
conformational dynamics in quantitative detail. In this perspective, we first
show that single molecule pulling experiments when combined with with theory
and simulations can be used to quantitatively explore the folding landscape of
nucleic acid hairpins, and riboswitches with tertiary interactions.
Applications to riboswitches, which are non-coding RNA elements that control
gene expression by undergoing dynamical conformational changes in response to
binding of metabolites, lead to an organization principle that assembly of RNA
is determined by the stability of isolated helices. We also point out the
limitations of single molecule pulling experiments, with molecular extension as
the only accessible parameter, in extracting key parameters of the folding
landscapes of RNA molecules.
