Practice question

Glycosylation adds monosaccharide residues with defined masses to proteins, altering function and stability. N-acetyl glucosamine, GlcNAc, exists as common modification in N-linked and O-linked glycans and O-GlcNAc signaling. Residue mass of HexNAc after dehydration during glycosidic bond formation is 203.079 Da, observed as +203 Da increment on peptide mass spectra. Detecting this shift indicates single GlcNAc attachment, distinct from 162 Da for hexose, 146 Da for fucose, or 291 Da for sialic acid. Recognition of +203 Da aids mapping of glycosylation sites in proteomics studies.