Tyrosine and lysine, shown in Fig. 9.1, are naturally occurring amino acids found in proteins. H₂N OH NH₂ HO tyrosine OH NH₂ lysine Fig. 9.1

1. (a)The isoelectric point of lysine is 9.47. Draw the structure of lysine at the stated pH in the boxes below. lysine at pH 7.00 lysine at pH 9.47 lysine at pH 12.00 [2][2]
2. (b)When ethanoic acid is treated with PCl₅ product D is formed. When D is added to tyrosine two different isomeric products, E and F, are formed. E has an ester linkage, F does not. Draw the structures of D, E and F in the boxes below. D E F [3][3]
3. (c)Complete Table 9.1 by drawing the structure of the organic product formed when tyrosine reacts with each named reagent. Ignore the directing effect of the –CH₂CHNH₂COOH substituent. Table 9.1 reagent | structure an excess of Br₂(aq) | an excess of NaOH(aq) | an excess of HNO₃(aq) | [3][3]
4. (d)A mixture of tyrosine and lysine can be separated by thin-layer chromatography. Under certain conditions the Rᶠ value of lysine is 0.14 and the Rᶠ value of tyrosine is 0.45.
5. (d)(i)Explain what is meant by Rᶠ value. [1][1]
6. (d)(ii)Suggest an explanation for the difference in Rᶠ values. [1][1]

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