-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 Hello Jacob,
I do not know the data, but the word 'fibre' sounds close to 'one-dimensional crystal', especially considering the screw axis you have in DNA, at least within the resolution limits that the pictures suggest. Cheers, Tim On 05/09/12 18:35, Jacob Keller wrote: > Well, what about the original DNA fiber diffraction images--no > microcrystals there, as far as I know, but one can clearly see the > stacking distances and the phosphate backbone. > > JPK > > On Wed, May 9, 2012 at 11:03 AM, Tim Gruene > <[email protected]> wrote: > > Dear Jacob, > > A protein would only scatter but not diffract, the latter - in my > understanding - being the result of constructive interference from > a regular array of unit cells . > > A powder pattern is the superposition of many small crystals > amongst which you don't observe interference. > > Tim > > On 05/09/12 16:16, Jacob Keller wrote: >>>> Dear Crystallographers, >>>> >>>> the "saxs on crystals" thread reminded me of a question I >>>> have had for a while, and never having collected data better >>>> than ~1.6 Ang or so, cannot answer myself from experience: I >>>> would think that there might be powder-like diffraction rings >>>> at distances corresponding to the various covalent bond >>>> lengths in proteins (1.2-1.5 Ang), but have never heard of >>>> such. My thinking is that the protein itself is essentially a >>>> powder sample within the unit cell consisting of many small, >>>> randomly-oriented molecules (amino acids) with their covalent >>>> bonds. Do the rings in fact exist, and if not, why not? Maybe >>>> the electron density is not as "atomic," or discrete, as the >>>> nuclei are? I wonder whether generally data collected to >>>> beyond ~1 Ang have an intensity "bump" at those covalent bond >>>> lengths, as I believe is seen in nucleic acid-containing >>>> structures at the base-stacking distance (at the right >>>> orientation)? >>>> >>>> Jacob >>>> > >> > > > - -- - -- Dr Tim Gruene Institut fuer anorganische Chemie Tammannstr. 4 D-37077 Goettingen GPG Key ID = A46BEE1A -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.12 (GNU/Linux) Comment: Using GnuPG with Mozilla - http://enigmail.mozdev.org/ iD8DBQFPqp7RUxlJ7aRr7hoRAtTyAKD92CJ7+MEWyfrhov9De2AoZsDiwwCeJwg3 FiAas+UvQaXpoRCsQ8cNGdI= =bguN -----END PGP SIGNATURE-----
