$$\begin{array}{l}
\text { Exhibit } \mathbf { 3 A } \text { (for this chapter) }\
\begin{array} { l l l l }
\text { Amino acid } & \boldsymbol { \alpha } \text {-carboxyl group pK a } & \boldsymbol { \alpha } \text {-amino group pK a } & \text { R-group pK } \
\hline \text { Ala } & 2.3 & 9.7 & \
\text { Arg } & 2.2 & 9.0 & 12.5 \
\text { Asn or Gln } & 2.1 & 9.0 & 4.0 \
\text { Asp or Glu } & 2.2 & 9.8 & 8.3 \
\text { Cys } & 1.7 & 10.8 & 6.0 \
\text { His } & 1.8 & 9.2 & \
\text { Ser } & 2.2 & 9.2 & 10.1
\end{array}
\end{array}$$
-Refer to Exhibit 3A. What is the order of the pIs in increasing order (from acid to base)?

Question

$$\begin{array}{l}
\text { Exhibit } \mathbf { 3 A } \text { (for this chapter) }\
\begin{array} { l l l l } 
\text { Amino acid } & \boldsymbol { \alpha } \text {-carboxyl group pK a } & \boldsymbol { \alpha } \text {-amino group pK a } & \text { R-group pK } \
\hline \text { Ala } & 2.3 & 9.7 & \
\text { Arg } & 2.2 & 9.0 & 12.5 \
\text { Asn or Gln } & 2.1 & 9.0 & 4.0 \
\text { Asp or Glu } & 2.2 & 9.8 & 8.3 \
\text { Cys } & 1.7 & 10.8 & 6.0 \
\text { His } & 1.8 & 9.2 & \
\text { Ser } & 2.2 & 9.2 & 10.1
\end{array}
\end{array}$$
-Refer to Exhibit 3A. What is the order of the pIs in increasing order (from acid to base)?

Quizplus · Accepted Answer

The pI of an amino acid is the pH at which the amino acid has no net charge. The pI is determined by the pKa values of the amino acid's ionizable groups. The pKa of an ionizable group is the pH at which the group is half-protonated. The higher the pKa, the more basic the group.The pI of an amino acid is typically between the pKa values of its ionizable groups. For example, the pI of alanine is 6.0, which is between the pKa values of its α-carboxyl group (2.3) and its α-amino group (9.7).The order of the pIs in increasing order (from acid to base) is:Aspartic Acid (2.8) < Cysteine (5.0) < Arginine (10.8) < Alanine (6.0) < Asparagine (8.8)