1. Histidine will show good buffering action around its pKa of 6.
  2. Predominant form of the peptide at pH 10:

    Peptide.

  3. The peptide bond has appreciable double-bond character, because of π interactions between the carbonyl bond and the lone pairs on the nitrogen atoms. For steric reasons, the trans form is energetically favoured, since it keeps the side groups?
  4. Primary, secondary, tertiary and quaternary protein structures:
    • Amino acid sequence - defined as the primary structure
    • A haem prosthetic group - quaternary (interaction between different molecules)
    • The multi-subunit nature of phosphofructokinase - quaternary
    • An antiparallel β sheet - secondary (interaction between peptide backbones)
    • An ATP binding domain - tertiary (interaction between side chains to form a coherent structure from α helices and β sheets.