Chapter 3, Problem 4P

(a1)

Summary Introduction

To determine: Equilibrium equations for three ionizations of histidine and assign pK_a value for each ionization state.

Introduction: Amino acids are the monomer units of proteins. These are basically organic compounds consisting of a carboxylic group (-COOH) and an amino group (-NH₂). Along with these functional groups, a side chain (R group) is also present in all the amino acids.

(a2)

Summary Introduction

To draw: Histidine structure in each ionization state.

Introduction: Histidine is a basic amino acid with lysine and arginine. Histidine consists of three ionizable groups. These are α-amino group, α-carboxylic acid group, and side chain amino group.

(a3)

Summary Introduction

To determine: The net charge on histidine molecule in each ionization state.

Introduction:

Histidine is a basic amino acid along with lysine and arginine. Histidine consists of three ionizable groups. These are α-amino group, α-carboxylic acid group, and side chain amino group.

(b)

Summary Introduction

To draw: The structures of histidine at pH 1, 4, 8, and 12.

Introduction:

pH is defined as the negative of base 10 logarithm of hydrogen ion concentration. It is a scale to determine the nature of an aqueous solution; acidic or alkaline.

(c1)

Summary Introduction

To determine: The net charge of histidine at pH 1, 4, 8, and 12.

Introduction:

pH is defined as the negative of base 10 logarithm of hydrogen ion concentration. It is a scale to determine the nature of an aqueous solution; acidic or alkaline.

(c2)

Summary Introduction

To determine: Whether histidine would migrate towards anode or cathode in an electric field for each pH.

Introduction:

pH is defined as the negative of base 10 logarithm of hydrogen ion concentration. It is a scale to determine the nature of an aqueous solution; acidic or alkaline.