Amino Acid Properties: Threonine, Lysine, and Tyrosine

a. Here are the amino acids threonine, lysine, and tyrosine:

Threonine: H | H3N--C--COOH | CH3

Lysine: H | H3N--C--COOH | CH2CH2CH2CH2NH2

Tyrosine: H | H3N--C--COOH | CH2--C6H4--OH

b. The side chains are circled. For threonine, it is the CH3 group; for lysine, it is the CH2CH2CH2CH2NH2 group; and for tyrosine, it is the CH2--C6H4--OH group.

c. Threonine is polar, lysine is basic, and tyrosine is polar.

d. Threonine will exist as a zwitterion at a pH of around 2.8-9.8, lysine at a pH of around 9.6-10.8, and tyrosine at a pH of around 5.4-10.1.

e. Threonine will be positively charged at a pH below 2.8, lysine at a pH below 9.6, and tyrosine does not have a positively charged state.

f. Threonine will be negatively charged at a pH above 9.8, lysine does not have a negatively charged state, and tyrosine will be negatively charged at a pH above 10.1.