The pivotal theory of molecular biology states that the structure of biomolecules is directly related to their function in living systems. In this way, the structural investigation of biological molecules allows understanding and intervening in the fundamental biological processes. Furthermore, the structural characterization of isolated biomolecules in the gas phase offers the advantage of determining their intrinsic structural properties free from environment perturbations. A particularly sensitive gas-phase technique to the finest structural details of biomolecules is cryogenic infrared spectroscopy. The scope of this thesis is to determine the gas-phase structure of a range of biologically relevant molecules in the gas phase. In the first part of this thesis we study the clustering of the amino acid serine into a protonated octamer. As a âmagic numberâ cluster it exhibits an unusually high abundance in the gas phase and an outstanding homochiral preference. We report the structure of the protonated serine octamer determined by a combination of experimental and computational techniques: gas-phase infrared spectroscopy of the helium-tagged protonated serine octamer cluster and ab initio molecular dynamics simulations. The found structure is surprisingly asymmetric and explains the homochiral preference of the cluster. In the second part, we introduce an isotopic labeling method for analyzing the conformational heterogeneity of glycans. Infrared-infrared double resonance spectroscopy performed on a helium-tagged protonated monosaccharide provides vibrational fingerprints of individual conformers and, together with quantum mechanical computations, is used to interpret the results from isotopic labeling. In the last part, cryogenic infrared spectroscopy gives insight into the migration of the electronic excitation between two aromatic chromophores of a model peptide. This is possible because the absorption bands in the highly-resolved infrared spectra of the excited states are sensitive to the localization of the electronic energy in each chromophore.