Comment by dekhn
3 days ago
I beleive fibre diffraction also works on parallel fibres (non-helical). For example, long chains of beta-sheet (look at beta keratin, which is one of the early non-helical structures analyzed by Astbury).
3 days ago
I beleive fibre diffraction also works on parallel fibres (non-helical). For example, long chains of beta-sheet (look at beta keratin, which is one of the early non-helical structures analyzed by Astbury).
Technically beta keratin is helical. That said you are correct, there is no requirement to be helical for fiber diffraction. It just turns out it's very difficult to have non helical uniaxial symmetry in nature.
When I was studying spindle shaped viruses by electron microscopy we'd get beautiful fiber diffraction patterns in the fourier transform of the micrographs. I always wanted to try and solve the helical parameters but never got around to it.
Beta keratin fibers are helical. (The pitch is much longer, but still helical, not alpha helices obvs).