What is a zwitterion in biochemistry?

A zwitterion is defined as a molecule that possesses both positive and negative charges but remains overall electrically neutral. This unique characteristic is often observed in amino acids at a certain pH level, typically around the isoelectric point, where the molecule has a protonated amino group (-NH3+) carrying a positive charge and a deprotonated carboxyl group (-COO−) carrying a negative charge.

This duality of charge enables zwitterions to play crucial roles in biochemical processes, such as protein structure and function, where the balance of charges influences solubility, reactivity, and interactions with other biomolecules. In contrast, a negatively charged molecule or a positively charged molecule would not be classified as a zwitterion, as they lack the simultaneous presence of opposing charges. Lastly, a neutral molecule, while having no net charge, does not exhibit the characteristic dual charge feature of zwitterions. Thus, the option that states a zwitterion features both positive and negative charges accurately captures its definition and role in biochemistry.