non-covalent complexes...
Non-covalent bonds between biomolecules (such as proteins or nucleic acids) are critical in maintaining the three-dimensional structure of large molecular complexes - the little machines that perform most of the cruicial functions in a cell. Many regulating mechanisms function via non-covalent interactions between these biomolecules or with specific ligands. Understanding these interactions is a vital part of understanding the biomolecular complexes as a functional unit.
