(a) Use the Data Booklet to draw the structure of the dipeptide val-lys. The peptide bond should be shown displayed.

1. (a)Use the Data Booklet to draw the structure of the dipeptide val-lys. The peptide bond should be shown displayed. [2][2]
2. (b)The isoelectric point is the pH at which an amino acid exists as a zwitterion. The isoelectric point of valine is 6.0 and of lysine is 9.8. A mixture of the dipeptide, val-lys, and its two constituent amino acids, valine and lysine, was analysed by electrophoresis using a buffer at pH 6.0. Draw and label three spots on the diagram of the electrophoresis paper to indicate the likely position of each of these three species after electrophoresis. Explain your answer. [Figure: Electrophoresis paper with a central line marked 'X' for mixture applied here, and '+' and '-' poles at either end.] explanation ................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................. [5][5]