Single molecules of beta-1 --> 6-linked d-glucose polysaccharides, when stretched in an atomic force microscope, display a hookean-like elasticity unusual for polymers. High-level ab initio calculations and microsecond-scale molecular dynamics simulations reveal that this elasticity is governed by force-induced rotations of the exocyclic group on the glucopyranose rings from their short and less energetic gt and gg conformations to the extended and high-energy tg state. These observations indicate that a simple stretching of 1 --> 6-linked glucose polysaccharides provide a unique means to control glucopyranose rotamer populations.