Chapter 17, Problem 29P

Draw the predominant form of the following amino acids at physiological pH (7.4):

1. a. Lysine
2. b. Arginine
3. c. tyrosine

Interpretation Introduction

Interpretation:

The predominant form of lysine at physiological $\text{pH }\left(\text{7}\text{.4}\right)$ has to be drawn.

Concept introduction:

Acid-base properties of Amino acids:

Every amino acid has a carbonyl group and an amino group, and each group can exist in an acidic form or a basic form, depending on $\text{pH}$ of the solution in which the amino acid is dissolved.

The compound exists primarily in the acidic form in solutions that are more acidic than their ${\text{pK}}_{\text{a}}$ values, and primarily in the basic form (without their protons) in solutions that are more basic than their ${\text{pK}}_{\text{a}}$ values.

At $\text{pH=}\text{7}$, $\text{pH}$ of the solution is greater than the ${\text{pK}}_{\text{a}}$ of the carboxyl group then carboxyl group is in the basic form, but less than the ${\text{pK}}_{\text{a}}$ of the protonated amino group then amino acid is in the acidic form.

Answer to Problem 29P

The predominant form of lysine at physiological $\text{pH }\left(\text{7}\text{.4}\right)$

  

Explanation of Solution

The predominant form of glutamine at physiological $\text{pH }\left(\text{7}\text{.4}\right)$

  

${\text{pK}}_{\text{a}}\text{, α-COOH = 2}\text{.17}$ Value is lesser than the given $\text{pH = 7}\text{.4}$; carbonyl group has to be in the basic form so carbonyl group is deprotonated and exist in negative charges (carboxylate ion); ${\text{pK}}_{\text{a}}{\text{, α-NH}}_3\text{ = 9}\text{.04}$ value is greater than the given $\text{pH = 7}\text{.4}$ so amino group must in the acidic form so the amino group gets protonated. The two amine groups do not protonated as the lone pairs involves in the delocalization.

Interpretation Introduction

Interpretation:

The predominant form of arginine at physiological $\text{pH }\left(\text{7}\text{.4}\right)$ has to be drawn.

Concept introduction:

Acid-base properties of Amino acids:

Every amino acid has a carbonyl group and an amino group, and each group can exist in an acidic form or a basic form, depending on $\text{pH}$ of the solution in which the amino acid is dissolved.

The compound exists primarily in the acidic form in solutions that are more acidic than their ${\text{pK}}_{\text{a}}$ values, and primarily in the basic form (without their protons) in solutions that are more basic than their ${\text{pK}}_{\text{a}}$ values.

At $\text{pH=}\text{7}$, $\text{pH}$ of the solution is greater than the ${\text{pK}}_{\text{a}}$ of the carboxyl group then carboxyl group is in the basic form, but less than the ${\text{pK}}_{\text{a}}$ of the protonated amino group then amino acid is in the acidic form.

Answer to Problem 29P

The predominant form of lysine at physiological $\text{pH }\left(\text{7}\text{.4}\right)$

  

Explanation of Solution

The predominant form of lysine at physiological $\text{pH }\left(\text{7}\text{.4}\right)$

  

${\text{pK}}_{\text{a}}\text{, α-COOH = 2}\text{.17}$ Value is lesser than the given $\text{pH = 7}\text{.4}$; carbonyl group has to be in the basic form so carbonyl group is deprotonated and exist in negative charges (carboxylate ion); ${\text{pK}}_{\text{a}}{\text{, α-NH}}_3\text{ = 9}\text{.04}$ value is greater than the given $\text{pH = 7}\text{.4}$ so amino group must in the acidic form so the amino group gets protonated. The two amine groups do not protonated as the lone pairs involves in the delocalization.

Interpretation Introduction

Interpretation:

The predominant form of tyrosine at physiological $\text{pH }\left(\text{7}\text{.4}\right)$ has to be drawn.

Concept introduction:

Acid-base properties of Amino acids:

Every amino acid has a carbonyl group and an amino group, and each group can exist in an acidic form or a basic form, depending on $\text{pH}$ of the solution in which the amino acid is dissolved.

The compound exists primarily in the acidic form in solutions that are more acidic than their ${\text{pK}}_{\text{a}}$ values, and primarily in the basic form (without their protons) in solutions that are more basic than their ${\text{pK}}_{\text{a}}$ values.

At $\text{pH=}\text{7}$, $\text{pH}$ of the solution is greater than the ${\text{pK}}_{\text{a}}$ of the carboxyl group then carboxyl group is in the basic form, but less than the ${\text{pK}}_{\text{a}}$ of the protonated amino group then amino acid is in the acidic form.

Answer to Problem 29P

The predominant form of tyrosine at physiological $\text{pH }\left(\text{7}\text{.4}\right)$

  

Explanation of Solution

The predominant form of tyrosine at physiological $\text{pH }\left(\text{7}\text{.4}\right)$

  

${\text{pK}}_{\text{a}}\text{, α-COOH = 2}\text{.20}$ Value is lesser than the given $\text{pH = 7}\text{.4}$; carbonyl group has to be in the basic form so carbonyl group is deprotonated and exist in negative charges (carboxylate ion); ${\text{pK}}_{\text{a}}{\text{, α-NH}}_3\text{ = 9}\text{.11}$ value is greater than the given $\text{pH = 7}\text{.4}$ so amino group must in the acidic form so the amino group gets protonated.