Chapter 21, Problem 56P

Decide if the side chains of the amino acid residues in the following peptides are nonpolar or polar, and label the hydrophobic and hydrophilic end of each peptide.

1. VLLFGEDEK
2. RKVSFLGAA

Interpretation Introduction

(a)

Interpretation:

The polarity of the side chains of the amino acid residue in the given peptide should be determined and also label the hydrophilic and hydrophobic ends of the given peptide.

VLLFGEDEK

Concept Introduction:

Amino acids are organic compounds containing two functional groups namely amino and carboxylic group. Amino group is attached to the alpha carbon, carbon adjacent to the carbonyl group making them alpha amino acids.

This table gives information about the polarity of the side chains:

Name of Amino Acid	One-letter abbreviation	Structure	Side chain Polarity	Side chain
Alanine	A		Nonpolar	Hydrophobic
Asparagine	N		Polar	Hydrophilic
Cysteine	C		Nonpolar	Hydrophobic
Glutamine	Q		Polar	Hydrophilic
Glycine	G		Nonpolar	Hydrophobic
Isoleucine	I		Nonpolar	Hydrophobic
Leucine	L		Nonpolar	Hydrophobic
Methionine	M		Nonpolar	Hydrophobic
Phenylalanine	F		Nonpolar	Hydrophobic
Proline	P		Nonpolar	Hydrophobic
Serine	S		Polar	Hydrophilic
Threonine	T		Polar	Hydrophilic
Tryptophan	W		Nonpolar	Hydrophobic
Tyrosine	Y		Polar	Hydrophilic
Valine	V		Nonpolar	Hydrophobic
Aspartic acid	D		Polar	Hydrophilic
Glutamic acid	E		Polar	Hydrophilic
Arginine	R		Polar	Hydrophilic
Histidine	H		Polar	Hydrophilic
Lysine	K		Polar	Hydrophilic

Answer to Problem 56P

The polarity of the side chains of amino acids are shown along with hydrophobic and hydrophilic end of the given peptide 'VLLFGEDEK' as follows:

Explanation of Solution

Side chains of amino acids are non-polar because only carbon and hydrogen atoms are present having very small dipole moment and tends to repel water. That's why non-polar amino acids are hydrophobic in nature.

Side chains of amino acids are polar because these proteins have those toms which are capable of forming hydrogen bonds have very high dipole moment and tends to attract water. That's why polar amino acids are hydrophilic in nature.

From the table, the sequence of peptide contains the following amino acids:

V = Valine is a non-polar amino acid.

L = Leucine is a non-polar amino acid.

F = Phenylalanine is a non-polar amino acid.

G = Glycine is a non-polar amino acid.

E = Glutamic acid is a polar amino acid.

D = Aspartic acid is a polar amino acid.

K = Lysine is a polar amino acid.

From the given peptide sequence 'VLLFGEDEK', Valine present at the right end and Lysine present at the left end of the sequence.

Valine is a non-polar amino acid and hydrophobic in nature.

Lysine is a non-polar amino acid and hydrophilic in nature.

Hydrophobic and hydrophilic ends along with polar and non-polar amino acids are indicated in the given sequence as follows:

Interpretation Introduction

(b)

Interpretation:

The polarity of the side chains of the amino acid residue in the given peptide should be determined and also label the hydrophilic and hydrophobic ends of the given peptide.

RKYSFLGAA

Concept Introduction:

Amino acids are organic compounds containing two functional groups namely amino and carboxylic group. Amino group is attached to the alpha carbon, carbon adjacent to the carbonyl group making them alpha amino acids.

Answer to Problem 56P

The polarity of the side chains of amino acids are shown along with hydrophobic and hydrophilic end of the given peptide 'RKYSFLGAA' as follows:

Explanation of Solution

Side chains of amino acids are non-polar because only carbon and hydrogen atoms are present having very small dipole moment and tends to repel water. That's why non-polar amino acids are hydrophobic in nature.

Side chains of amino acids are polar because these proteins have those toms which are capable of forming hydrogen bonds have very high dipole moment and tends to attract water. That's why polar amino acids are hydrophilic in nature.

From the table, the sequence of peptide 'RKYSFLGAA' contains the following amino acids:

R = Arginine is a polar amino acid.

K = Lysine is a polar amino acid.

Y = Tyrosine is a polar amino acid.

S = Serine acid is a polar amino acid.

F = Phenylalanine is a non-polar amino acid.

L = Leucine is a non-polar amino acid.

G = Glycine is a non-polar amino acid.

A = Alanine is a non-polar amino acid.

From the given peptide sequence 'RKYSFLGAA', Arginine present at the right end and Alanine present at the left end of the sequence.

Arginine is a polar amino acid and hydrophilic in nature.

Alanine is a non-polar amino acid and hydrophobic in nature.

Hydrophobic and hydrophilic ends along with polar and non-polar amino acids are indicated in the given sequence as follows: