The dynamic structure factor of semiflexible macromolecules in solution is briefly discussed. Particularly, the theoretical calculations are compared with experimental data of the extracellular, anionic polysaccharide gellan in dilute solution. Our theoretical calculations agree very well with the experimental data. Furthermore,:he interpretation of the initial decay rate of the dynamic structure factor as a characteristic frequency in the sense of dynamic scaling is discussed. As a result of our calculations, the influence of polydispersity on the shape of the dynamic structure factor at large scattering vectors is found to be small.