Untitled

   H      H      H
   |      |      |
H-C-C=O  H-C-C=O  H-C-C=O
   | |    | |    | |
H-N-C-H  H-N-C-H  H-N-C-H
   |      |      |
   A      G      S

   ↓      ↓      ↓

  H-C-C=O  H-C-C=O
   | |    | |
  H-N-C-H  H-N-C-H
     |      |
     A      G      S