Chapter 16.2, Problem 16.12QAP

Interpretation Introduction

Interpretation: The overall charge of a polar neutral amino acid at a pH above its pI.

Concept introduction:

➢ Amino acid: Any molecule contains both amino and acid group

Ex:

➢ The $\text{R }-$ group is polar $\left(-{\text{ CH}}_2-\text{OH,}-{\text{CH}}_2-\text{S}-{\text{CH}}_3\text{ etc}\right)$ then called polar amino acid.

➢ The amino acid has two groups

One acts base and other acts as acid. So net charge or form of amino acid depends upon$\text{pH value}$

➢ Amino acid is any molecule that contains both amino and acid group. If $\text{pH = pI}$ net charge on amino acid is zero called zwitterion form contains equal no of $\text{+ ve and }-\text{ ve}$ charge.

➢ If $\text{pH > pI}$, then at this ${\text{pH H}}_3{\text{N}}^{+}-$

➢ acts as acid and donates one proton $\left({\text{H}}^{+}\right)$

➢ to form $-{\text{NH}}_2$

And it has total charge $=1-$

➢ If$\text{pH < pI}$, then

Acts as base and accept one proton form solution and convert to

. So at such $\text{pH }$

it has total charge $=1+$