Chapter 18, Problem 18.179P

(a)

Interpretation Introduction

Interpretation:

Variation in solubility of casein with pH has to be explained.

Concept Introduction:

Casein contains many carboxyl groups in the side chain. Carboxyl group $\left(\text{COOH}\right)$ contains an acidic proton which can be easily donated. Carboxylic acid in basic medium will remove this proton and exists as stable carboxylate anion $\left({\text{COO}}^{\text{-}}\right).$

Water is polar solvent. Hence polar compounds will dissolve easily in water.

(b)

Interpretation Introduction

Interpretation:

Variation in solubility of histone with pH has to be explained.

Concept Introduction:

Histone contain ${\text{-NH}}_{\text{2}}$ and $\text{=NH}$ in its side chain. Nitrogen in these groups can accept proton and become positively charged species. In acidic medium, proton concentration will be more so ${\text{-NH}}_{\text{2}}$ and $\text{=NH}$ takes proton and becomes positively charged species.

Water is polar solvent. Hence polar compounds will dissolve easily in water.