Topic overview

Start with the big picture

The lesson surveys complementary approaches to determining macromolecular size and shape. It distinguishes radius of gyration, which reflects mass distribution, from hydrodynamic radius, which describes how a molecule behaves as it diffuses in solvent, and from contour length. Dynamic and static light scattering provide different information, while SAXS and SANS characterize dimensions and low-resolution shape. Analytical ultracentrifugation, size-exclusion chromatography, and viscometry offer additional routes to infer mass, hydrodynamic behavior, or conformation. Imaging methods such as electron microscopy and atomic force microscopy can reveal morphology and topography, while fiber diffraction, NMR diffusion, and fluorescence correlation spectroscopy provide other structural or diffusion-based measurements. The methods are interpreted using appropriate models and awareness of what each measurement represents.