Peptide Structures Are Easy to Draw

Prefixes like tri- or octa- denote peptides with three or eight residues, respectively, not those with three or eight peptide bonds. By convention, peptides are written with the residue that bears the free α-amino group at the left. To draw a peptide, use a zigzag to represent the main chain or backbone. Add the main chain atoms, which occur in the repeating order: α-nitrogen, α-carbon, carbonyl carbon. Now add a hydrogen atom to each α-carbon and to each peptide nitrogen, and an oxygen to the carbonyl carbon. Finally, add the appropriate R groups (shaded) to each α-carbon atom.
Three-letter abbreviations linked by straight lines represent an unambiguous primary structure. Lines are omitted for single-letter abbreviations. Where there is uncertainty about the order of a portion of a polypeptide, the questionable residues are enclosed in brackets and separated by commas.
                                            Glu- Ala - Lys - Gly - Tyr - Ala
                                              E      A      K       G     Y      A