which of the following features of vancomycin distinguishes it from most other cellular peptides? choose one or more: a. a massive seven-module enzyme is required for glycosylation, chlorination, and side-chain linking of the precursor heptapeptide. b. the heptapeptide backbone is synthesized independently of a ribosome. c. it includes unusual amino acids not normally found in proteins. d. its synthesis requires a modified genetic code. e. some amino acids are present in the d-form rather than the l-form.