Question

The X-ray crystallographic analysis of a protein often fails to reveal the positions of the first few and/or the last few residues of a polypeptide chain. Explain.

Short answer

X-ray crystallography fails to reveal the residues at the beginning of peptide chain as well as the end of peptide chain.

The string of missing residues are termed as N-terminal when they occur at the beginning of polypeptide chain. While they are termed C-terminal when they are present at the end of polypeptide chain.

Step-by-step solution

Explanation of x-ray crystallography

X-ray crystallography is a technique which is aimed at revealing the structure of matter at the atomic level. It reveals three dimensional position precisely of most of the atoms in protein molecule. This is because x-rays and covalent bonds have almost similar wavelength.

Missing residues in x-ray cystallography

X-ray crystallography fails to reveal the residues at the beginning of peptide chain i.e. at N-terminal as well as the end of peptide chain i.e. at C-terminal.