What is responsible for the accumulation of negatively charged proteins just inside the cell membrane?

The accumulation of negatively charged proteins just inside the cell membrane is primarily attributed to the action of the sodium-potassium pump, often referred to as the Na/K pump. This pump plays a critical role in maintaining the resting membrane potential of the cell by actively transporting sodium ions (Na+) out of the cell and potassium ions (K+) into the cell.

As the Na/K pump operates, it moves three sodium ions out for every two potassium ions it brings in. This consistent exchange creates an imbalance in ionic concentrations across the cell membrane, resulting in a higher concentration of positive charges outside the cell in comparison to inside. Consequently, the interior of the cell develops a negative charge primarily due to the presence of large, negatively charged proteins and anions that are unable to cross the cell membrane.

Furthermore, the pump's activity helps to maintain a polarized state and prevents the accumulation of sodium ions within the cell, which contributes to the overall negative charge. Thus, the function of the Na/K pump is integral to creating and sustaining the electrochemical gradient necessary for various cellular activities, including action potential generation in excitable tissues.