I have looked through my notes and book and can't find the answer so any help would be great. "In x-ray crystallography it is imperative that 3D crystals of highly pure protein be grown in the lab. Why is this necessary? In other words, why can't an x-ray source generate a diffration pattern from a single molecule or even 2D crystals?

You cannot use a single protein to generate a diffraction pattern because how will you know how the protein is orientated? It could be facing forward, or upside down, or on its side, etc. and you will get a different diffraction pattern each time.

 

2D crystals, I don't know what that means. How can you even make a 2D crystal?

 

It has to be 3D crystal so that the protein is all orientated in a highly organized manner so that you can generate a diffraction pattern that you know is right for the protein.

Thanks for the quick reply!