a) The following sequence represents part of the primary structure of collagen: ?-Pro-Pro-?-Ala-Pro-?-Pro-Gln-? What amino acid is represented in the sequence by a question mark? Enter your answer as the three-letter amino acid abbreviation. b) Proline and hydroxyproline make up about 30% of the remaining residues. The structure of proline is shown at right. Modify the structure so that it represents hydroxyproline. Modify the structure as needed by removing and/or adding atoms or bonds. c) Which of the following bonds stabilize the collagen triple helix? H H N- HH H O || H -R hydrogen bonds between charged amino acids hydrogen bonds between hydroxyproline residues ionic bonds between amino acid side chains hydrogen bonds between N-H and C=O