Which statement describes the behavior of proteins at a pH above their isoelectric point (pI)?

At a pH above their isoelectric point (pI), proteins behave in a specific way due to the ionization of their side chains and the overall charge balance. The isoelectric point represents the pH at which a protein has no net charge because the positive and negative charges are balanced.

When the pH is raised above the pI, the environment becomes less favorable for protonation of the acidic groups of the amino acids, and those groups lose protons (H+). As a result, more acidic side chains are negatively charged at this higher pH. Conversely, the basic side chains that might accept protons are already in a less favorable state for further protonation. Consequently, the overall charge of the protein becomes negative at pH levels above the pI. This negatively charged state leads to a range of behaviors pertaining to solubility and interactions with other molecules but is most simply defined in terms of charge.

Therefore, at a pH above their isoelectric point, proteins will generally be negatively charged. This concept is critical in understanding protein behavior in biochemical reactions and separation techniques, like electrophoresis, where the charge influences migratory behavior in an electric field.