This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Structure & Function of Protein, Subject name: Biochemistry
Tertiary structure of protein is best determined by: 
Select and explain. 
A. Chromatography, B. X- Ray diffraction crystallography, C. Electrophoresis, D. Mass spectrometry
B: X- Ray diffraction crystallography
Answer: B: X- Ray diffraction crystallography 
Explanation: Ans. B. X- Ray diffraction crystallographyTertiary structure is best visualized by X-ray crystallography and NMR (Nuclear magnetic Resonance) spectroscopy. X-rayCrystallography was the first method used to determine the structure of proteins. X-ray crystallography is one of the best methods because the wavelength of an x-ray is similar to that of covalent bonds found throughout proteins, creating a clearer visualization of a molecule's structure. The scattering of x-rays by electrons is analyzed to determine the structure of proteins. In order to use x-ray crystallography, the protein in question must be in crystal form. Some proteins crystallize readily, while others do not. For those proteins that do not crystallize readily, nuclear magnetic resonance (NMR) spectroscopy must be used to determine its structure.