Originally, a portion of a polypeptide looked like this: ala…

Originally, a portion of a polypeptide looked like this: alanine, glutamic acid, glycine, serine, isoleucine   After a base-pair substitution mutation occurred, the same portion of the polypeptide looks like this: alanine, glutamic acid, glycine, cysteine, isoleucine   What type of mutation occurred, based on the change to the polypeptide?