1. a. (i) Explain the term isoelectric point (pl) in relation to amino acids. [2 marks] (ii) Calculate the isoelectric point of lysine and glutamic acid, Figure 1. pk = 10.79 pka = 4.25 O pkg = 2.19 o pka = 2.18 H3N HO OH OH NH3 NH3 pk = 9.67 pk = 8.95 lysine glutamic acid Figure 1 [4 marks] (iii) Phenylalanine C can be synthesised from 3-phenylpropanoic acid A through intermediate B using the well-known Hell-Vollhard-Zelinsky reaction shown in Figure 2. PBr3, Br2 NH3 OH CH,Bro2 OH NH2 B A Figure 2 Identify the structure of intermediate B in Figure 2. [2 marks] (iv) Draw the mechanism for the formation of intermediate B from 3- phenylpropanoic acid A, Figure 2. [6 marks]