Question

Student Name: ID#: Section: 01 2) Lysine is a basic amino acid and has the following structure at low pH: (25 points) 0 HN-CH-C OH рка, рКа рКак 2.18 8.95 10.79 (CH2)4 ΝΗ, If this amino acid is titrated with a strong base answer the following questions: 1. Write the dissociation equation for Lysine and show the pH at each dissociation step. [10 pts] 2. Find the charge for the amino acid structure at each dissociation step. [6 pts] 3. Identify the structure of the Zwitterion. [4 pts] 4. Calculate the pl value for Lysine, [5 pts)

Answer 1

1. 2. The net charge before pka 1 = +2

pka3 14 13 12 It 10 pla2 PH 8 7 pkal 0.5 105 2.0 2.5 3.0 3.5 [OH] + CH₂ - CH₂ - CH₂ -CH ₂ ~NH₂ CHA-CH2-CH2-CH2- HNAC-Coon a H₂N- & coopka 2 PRI H CH₂ - CH₂ - CH₂ - CH₂ -NH2 eka 3 H₂N-C-cool ANC - CH₂ CH₂ - CH₂ Ch 14 H coon NH3 -# 쓰

The net charge between pKa1 and pKa2 = +1

The net charge between pKa2 and pKa3 = 0

The net charge after pKa3 = -1

3. The structure of the zwitterion is the structure exists between pKa 2 and pKa3

4. The pI value is the pH value at which the net charge of the protein is zero.

The pI value must lie in between pKa 2 and pKa 3.

pI = (8.95+10.97)/2 = 9.96