If the pH is greater than the pI in electrophoresis, what charge will the molecule carry?

In the context of electrophoresis and protein behavior, the pI, or isoelectric point, is the pH at which a molecule carries no net electric charge. If the pH of the environment is greater than the pI, this indicates that the environment is more basic than the pI. At a pH above the pI, the carboxyl groups of amino acids tend to lose protons, giving them a negative charge, while the amino groups may already be fully protonated or neutral depending on the specific conditions.

Proteins and other molecules that are charged will move in an electric field, with negatively charged species moving towards the anode (positive electrode) and positively charged species moving towards the cathode (negative electrode). In this scenario, since the pH is greater than the pI, the molecule in question will carry a net negative charge and will migrate towards the anode during electrophoresis.

This understanding helps clarify the behavior of biomolecules in different pH environments during techniques like electrophoresis, reinforcing the significance of the pI in determining the net charge and, consequently, the movement of these molecules in response to an electric field.