Chapter 27, Problem 27.61AP

Interpretation Introduction

(a)

Interpretation:

The explanation for alanine which has different optical rotation in water, $1\text{ M}$ $\text{HCl}$, and $1\text{ M}$$\text{NaOH}$ is to be stated.

Concept introduction:

The amino acid is made of two functional groups an amine group, $-{\text{NH}}_{\text{2}}$ and a carboxyl group, $-\text{COOH}$. Along with a side chain is also attached to the center carbon atom due to which each amino acid is distinguished. The amino acid alanine contains a $-{\text{CH}}_{\text{3}}$ side chain.

Answer to Problem 27.61AP

Each solvent rotates the alanine molecule to a different angle due to the formation of different complex formation and so it gives rise to different optical rotation in different solvents.

Explanation of Solution

The structure of alanine is shown below.

Figure 1

Alanine is an optically active compound. It rotates the plane of polarized light. The reaction of alanine with water, $1\text{ M}$ $\text{HCl}$, and $1\text{ M}$$\text{NaOH}$ forms a complex which is shown below.

Figure 2

The optical rotation of alanine is measure by Circular Dichroism (CD). It involves circularly polarized light absorption. It measures the angle at which the plane-polarized light is rotated by the molecule. Each solvent rotates the alanine molecule to a different angle, due to this it gives rise to different optical rotation in different solvents.

Conclusion

The alanine has different optical rotation in water, $1\text{ M}$ $\text{HCl}$, and $1\text{ M}$$\text{NaOH}$. This is because of different solvent molecule rotates the alanine molecule to a different angle.

Interpretation Introduction

(b)

Interpretation:

The explanation for two known mono $-N-$ acetyl derivatives of lysine is to be stated.

Concept introduction:

The amino acid is made of two functional groups an amine group, $-{\text{NH}}_{\text{2}}$ and a carboxyl group, $-\text{COOH}$. Along with a side chain is also attached to the center carbon atom due to which each amino acid is distinguished. The amino acid lysine contains a $-{\left({\text{CH}}_{\text{2}}\right)}_{\text{4}}{\text{NH}}_{\text{2}}$ side chain.

Answer to Problem 27.61AP

Due to the presence of two amine groups in lysine molecule. It may undergo acetylation reaction from either side and form mono $-N-$ acetyl derivatives of lysine.

Explanation of Solution

The structure of amino acid lysine is shown below.

Figure 3

The structure of the lysine molecule contains two amine group one at the $\text{α}$ carbon and other at the side chain. Therefore, it has the potential to undergo acetylation reaction from two sides which results in the formation of two mono $-N-$ acetyl derivatives of lysine. The product obtained after the acetylation reaction of lysine is shown below.

Figure 4

Conclusion

The two mono $-N-$ acetyl derivatives of lysine are possible. This is because of the presence of two amine groups which undergo acetylation reaction from either side and form mono $-N-$ acetyl derivatives of lysine.

Interpretation Introduction

(c)

Interpretation:

The explanation for fact that the peptide $\text{Gly}-\text{Ala}-\text{Arg}-\text{Ala}-\text{Glu}$ which is hydrolyzed by trypsin in water at $\text{pH}=8$ but remains inert to trypsin in $8\text{ M}$ urea $\text{pH}=8$ is to be stated.

Concept introduction:

The amino acid is made of two functional groups an amine group $-{\text{NH}}_{\text{2}}$ and a carboxyl group $-\text{COOH}$. Along with a side chain is also attached to the center carbon atom due to which each amino acid is distinguished. Urea at basic conditions is known to be a denaturation agent of protein.

Answer to Problem 27.61AP

The compound urea under basic conditions acts as a denaturation agent which breakdown the protein molecule bonding. Due to this, the peptide, $\text{Gly}-\text{Ala}-\text{Arg}-\text{Ala}-\text{Glu}$ which is hydrolyzed by trypsin in the water at $\text{pH}=8$ but remains inert to trypsin in $8\text{ M}$ urea $\text{pH}=8$.

Explanation of Solution

The protein molecule is composed of four types of structure primary, secondary, tertiary and quarternary. The enzyme trypsin hydrolyzes the peptide, $\text{Gly}-\text{Ala}-\text{Arg}-\text{Ala}-\text{Glu}$ in the water at $\text{pH}=8$ which results in the dissociation of an amide linkage. When the same peptide is treated with urea at same $\text{pH}$, it breaks the tertiary and quarternary structure of the protein and does not hydrolyze the peptide. It causes denaturation of protein by breaking the internal hydrogen bonding of the protein molecule.

Conclusion

The peptide $\text{Gly}-\text{Ala}-\text{Arg}-\text{Ala}-\text{Glu}$ which is hydrolyzed by trypsin in the water at $\text{pH}=8$ but remains inert to trypsin in $8\text{ M}$ urea $\text{pH}=8$. This is because of urea under basic conditions acts as a denaturation agent which breakdown the protein molecule bonding.

Interpretation Introduction

(d)

Interpretation:

The explanation for the peptide containing cysteine on reaction with ${\text{HSCH}}_{\text{2}}{\text{CH}}_{\text{2}}\text{OH}$ and aziridine may cleaved by trypsin at the modified cysteine residue is to be stated.

Concept introduction:

The amino acid is made of two functional groups an amine group, $-{\text{NH}}_{\text{2}}$ and a carboxyl group, $-\text{COOH}$. Along with a side chain is also attached to the center carbon atom due to which each amino acid is distinguished. The amino acid cysteine contains a $-{\text{CH}}_{\text{2}}\text{SH}$ side chain.

Answer to Problem 27.61AP

The generation of lysine type molecule at the end of the reaction which is cleaved by trypsin enzyme. Due to this, the peptide containing cysteine on reaction with ${\text{HSCH}}_{\text{2}}{\text{CH}}_{\text{2}}\text{OH}$ and aziridine may cleaved by trypsin at the modified cysteine residue.

Explanation of Solution

The structure of the cysteine molecule is shown below.

Figure 5

The same molecule in peptides exists as a disulfide bond. The disulfide bond of cysteine in the protein molecule is shown below.

Figure 6

When this protein molecule with a disulfide bond is treated with ${\text{HSCH}}_{\text{2}}{\text{CH}}_{\text{2}}\text{OH}$ which dissociates the disulfide bond. It results in the formation of a thiol group and $2,2\text{'}-\text{disulfanediyldiethanol}$. The reaction of a disulfide bond with ${\text{HSCH}}_{\text{2}}{\text{CH}}_{\text{2}}\text{OH}$ is shown below.

Figure 7

The thiol group is then reacted with the aziridine molecule which results in the formation of a lysine type molecule. This reaction is shown below.

Figure 8

This lysine type molecule then reacts with trypsin enzyme which cleaves arginine and lysine molecule. Due to this, the trypsin enzyme reacts with the modified cysteine residues.

Conclusion

The peptide containing cysteine on reaction with ${\text{HSCH}}_{\text{2}}{\text{CH}}_{\text{2}}\text{OH}$ and aziridine may cleaved by trypsin at the modified cysteine residue. This is because of the generation of lysine type molecule at the end of the reaction which is cleaved by trypsin enzyme.

Interpretation Introduction

(e)

Interpretation:

The explanation for the formation of two separable methionine sulfoxides from the oxidation of $\text{L}-\text{methionine}$ with ${\text{H}}_{\text{2}}{\text{O}}_{\text{2}}$ is to be stated.

Concept introduction:

The amino acid is made of two functional groups an amine group, $-{\text{NH}}_{\text{2}}$ and a carboxyl group, $-\text{COOH}$. Along with a side chain is also attached to the center carbon atom due to which each amino acid is distinguished. The amino acid methionine contains $-{\text{CH}}_{\text{2}}{\text{CH}}_{\text{2}}{\text{SCH}}_{\text{3}}$ side chain.

Answer to Problem 27.61AP

The application of a certain amount of energy which converts one form to another form of structure. Due to this, the formation of two separable methionine sulfoxides from the oxidation of $\text{L}-\text{methionine}$ with ${\text{H}}_{\text{2}}{\text{O}}_{\text{2}}$ is possible.

Explanation of Solution

The structure of methionine is shown below.

Figure 9

The resonance structure of sulfoxides with two different groups is shown below.

Figure 10

The conversion of one structure to another structure at room temperature requires a certain amount of energy. Therefore, on the application of that amount of energy, the two forms of $\text{L}-\text{methionine}$ which are separable at room temperature are formed. The structure of two different forms of $\text{L}-\text{methionine}$ is shown below.

Figure 11

Conclusion

The formation of two separable methionine sulfoxides from the oxidation of $\text{L}-\text{methionine}$ with ${\text{H}}_{\text{2}}{\text{O}}_{\text{2}}$ is possible. This is because of the application of a certain amount of energy which converts one form to another form of structure. They are separable at room temperature.