What is the molecular basis for the observation that the overall charge on a protein becomes increasingly positive as pH drops and more negative as pH increases?

Overall charge on protein becomes increasingly positive as pH decreases while overall charge on protein becomes negative as pH increases.

Explanation:

It is noticeable that protein are made up of amino acids which contain amine and Carboxyl functional groups.

Protein molecules in aqueous solution become positively charged (Protonated) as pH drops because of the fact that carboxylic acids become less negatively charged as the pH goes on to drop while amine become more positively charged.

Whereas overall charge on protein becomes more negative as pH increases because Acidic groups become more negatively charged while the basic group become less positively charged.