An amphoteric molecule can be negatively or positively charged. Changing the pH using buffers will alter the charge and magnitude of the charge.
A molecule with this amphoteric ability is sometimes referred to as an ampholyte or, by the older term, zwitterion.
Proteins with their ionizable amino and carboxyl groups are amphoteric. Nucleic acids (deoxyribonucleic acid or DNA and ribonucleic acid or RNA) are charged and thus are amphoteric.
