Glycine-the primary structure of collagen peptides consists of repeating tripeptides with a gly-x-y motif, where gly is glycine and x and y are any amino acid. the small ch2 group connecting the amino and carboxyl groups of glycine contrasts with the larger connecting groups and side chains of other amino acids. the small volume of glycine molecules is crucial for the helix secondary structure of collagen peptides. this in turn is necessary for their tertiary helical structure and their assembly into quaternary tripeptide, triple-helix structures. the most severe clinical phenotypes caused by amino acid substitutions in collagen peptides are those affecting glycine that prevent alpha helix formation. the child has a disorder called stickler syndrome (108300) that exhibits autosomal dominant inheritance.
