The OH group on the side chain of serine is not deprotonated at a pH of 12. However, the OH group on the side chain of tyrosine is deprotonated at a pH of 12. This can be verified by inspecting the pK_avalues in the following table. Suggest an explanation for the difference in acid-base properties between these two OH groups.

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THE PK,VALUES FOR TWENTY NATURALLY OCCURRING AMINO ACIDS a-NH3* a-COOH SIDE CHAIN AMINO ACID Alanine 2.34 9.69 Arginine 2.17 9.04 12.48 Asparagine 2.02 8.80 Aspartic acid 1.88 9.60 3.65 Cysteine 1.96 10.28 8.18 Glutamic acid 9.67 2.19 4.25 Glutamine 9.13 2.17 Glycine 2.34 9.60 Histidine 9.17 1.82 6.00 Isoleucine 2.36 9.60 2.36 9.60 Leucine 8.95 Lysine 2.18 10.53 Methionine 9.21 2.28 Phenylalanine 1.83 9.13 Proline 10.60 1.99 Serine 2.21 9.15 Threonine 2.09 9.10 Tryptophan 2.83 9.39 Tyrosine 2.20 9.11 10.07 Valine 2.32 9.62 T|||||||