Chapter 29, Problem 29.38P

What is the predominant form of each of the following amino acids at $\text{pH}=11$? What is the overall charge on the amino acid? (a) valine; (b) proline; (c) glutamic acid; (d) lysine

Interpretation Introduction

(a)

Interpretation: The predominant form of valine at $\text{pH}=11$ and the overall charge on it is to be predicted.

Concept introduction: At isoelectric point, the amino acids exist in their neutral form. The amine groups exists as $-\stackrel{+}{\text{N}}{\text{H}}_3$ and carboxyl groups as $-{\text{COO}}^{-}$. The overall charge on an amino acid at isoelectric point is $0$.

Answer to Problem 29.38P

The predominant form of valine at $\text{pH}=11$ is,

The overall charge on it is $-1$.

Explanation of Solution

At isoelectric point, the amino acids exist in their neutral form. The amine groups exists as $-\stackrel{+}{\text{N}}{\text{H}}_3$ and carboxyl groups as $-{\text{COO}}^{-}$. However, when the $\text{pH}$ of solution goes above isoelectric point, the amine group and carboxyl group exists as $-{\text{NH}}_{\text{2}}$ and $-{\text{COO}}^{-}$, respectively.

The isoelectric point of valine is $6.00$. Therefore, the predominant form of valine at $\text{pH}=11$ is,

Figure 1

The overall charge on valine at $\text{pH}=11$ is $-1$.

Conclusion

The predominant form of valine at $\text{pH}=11$ is,

The overall charge on it is $-1$.

Interpretation Introduction

(b)

Interpretation: The predominant form of proline at $\text{pH}=11$ and the overall charge on it is to be predicted.

Concept introduction: At isoelectric point, the amino acids exist in their neutral form. The amine groups exists as $-\stackrel{+}{\text{N}}{\text{H}}_3$ and carboxyl groups as $-{\text{COO}}^{-}$. The overall charge on an amino acid at isoelectric point is $0$.

Answer to Problem 29.38P

The predominant form of proline at $\text{pH}=11$ is shown in Figure 2 and the overall charge on it is $-1$.

Explanation of Solution

At isoelectric point, the amino acids exist in their neutral form. The amine groups exists as $-\stackrel{+}{\text{N}}{\text{H}}_3$ and carboxyl groups as $-{\text{COO}}^{-}$. However, when the $\text{pH}$ of solution goes above isoelectric point, the amine group and carboxyl group exists as $-{\text{NH}}_{\text{2}}$ and $-{\text{COO}}^{-}$, respectively.

The isoelectric point of proline is $6.30$. Therefore, the predominant form of proline at $\text{pH}=11$ is,

Figure 2

The overall charge on proline at $\text{pH}=11$ is $-1$.

Conclusion

The predominant form of proline at $\text{pH}=11$ is and the overall charge on it is $-1$.

Interpretation Introduction

(c)

Interpretation: The predominant form of glutamic acid at $\text{pH}=11$ and the overall charge on it is to be predicted.

Concept introduction: At isoelectric point, the amino acids exist in their neutral form. The amine groups exists as $-\stackrel{+}{\text{N}}{\text{H}}_3$ and carboxyl groups as $-{\text{COO}}^{-}$. The overall charge on an amino acid at isoelectric point is $0$.

Answer to Problem 29.38P

The predominant form of glutamic acid at $\text{pH}=11$ is,

The overall charge on it is $-2$.

Explanation of Solution

At isoelectric point, the amino acids exist in their neutral form. The amine groups exists as $-\stackrel{+}{\text{N}}{\text{H}}_3$ and carboxyl groups as $-{\text{COO}}^{-}$. However, when the $\text{pH}$ of solution goes above isoelectric point, the amine group and carboxyl group exists as $-{\text{NH}}_{\text{2}}$ and $-{\text{COO}}^{-}$, respectively.

The isoelectric point of glutamic acid is $3.08$. Therefore, the predominant form of glutamic acid at $\text{pH}=11$ is,

Figure 3

The overall charge on glutamic acid at $\text{pH}=11$ is $-2$.

Conclusion

The predominant form of glutamic acid at $\text{pH}=11$ is,

The overall charge on it is $-2$.

Interpretation Introduction

(d)

Interpretation: The predominant form of lysine at $\text{pH}=11$ and the overall charge on it is to be predicted.

Concept introduction: At isoelectric point, the amino acids exist in their neutral form. The amine groups exists as $-\stackrel{+}{\text{N}}{\text{H}}_3$ and carboxyl groups as $-{\text{COO}}^{-}$. The overall charge on an amino acid at isoelectric point is $0$.

Answer to Problem 29.38P

The predominant form of lysine at $\text{pH}=11$ is,

The overall charge on it is $-1$.

Explanation of Solution

At isoelectric point, the amino acids exist in their neutral form. The amine groups exists as $-\stackrel{+}{\text{N}}{\text{H}}_3$ and carboxyl groups as $-{\text{COO}}^{-}$. However, when the $\text{pH}$ of solution goes above isoelectric point, the amine group and carboxyl group exists as $-{\text{NH}}_{\text{2}}$ and $-{\text{COO}}^{-}$, respectively.

The isoelectric point of lysine is $9.74$. Therefore, the predominant form of lysine at $\text{pH}=11$ is,

Figure 4

The overall charge on lysine at $\text{pH}=11$ is $-1$.

Conclusion

The predominant form of lysine at $\text{pH}=11$ is shown in Figure 4 and the overall charge on it is $-1$.