Chapter 20, Problem 20.104EP

(a)

Interpretation Introduction

Interpretation: The hydrophobic interaction is whether a covalent bond or noncovalent interaction has to be stated.

Concept introduction: The hydrophobic interaction exists between the nonpolar R groups of the amino acids.  In aqueous solvent, the nonpolar side chains of the amino acids point inwards, that is away from the polar water molecules.

(b)

Interpretation Introduction

Interpretation: The hydrogen bond is whether a covalent bond or noncovalent interaction has to be stated.

Concept introduction: The hydrogen bond exists between the polar R groups of the amino acids.  Different polar side chains, mostly that have a functional group can involve in hydrogen bonding.

(c)

Interpretation Introduction

Interpretation: The disulphide bond is whether a covalent bond or noncovalent interaction has to be stated.

Concept introduction: The disulphide bond exists between the $\text{SH}$ groups of two cysteine amino acids.  It is the strongest interaction out of the other four interactions.

(d)

Interpretation Introduction

Interpretation: The electrostatic interaction is whether a covalent bond or noncovalent interaction has to be stated.

Concept introduction: The electrostatic interaction exists between the acidic R group of an amino acid and the basic R group of the other amino acid.  The acidic side chain becomes negatively charged and the basic side chain becomes positively charge at an apt pH.