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: > -----BEGIN PGP SIGNED MESSAGE----- > Hash: SHA1 > > 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/ > > iD8DBQFPqpVlUxlJ7aRr7hoRAhZqAJ9M49u+cYsX+AhzRlYKOCTX8YCsbQCgzFBi > ZV+cZCyQgGLusrnufngyZ5A= > =cuQy > -----END PGP SIGNATURE----- > -- ******************************************* Jacob Pearson Keller Northwestern University Medical Scientist Training Program email: [email protected] *******************************************
