What type of transport protein generates voltage across a membrane?

The correct answer is the electrogenic pump, which plays a crucial role in generating voltage across a membrane. An electrogenic pump is a type of active transport protein that moves ions across a membrane, leading to an unequal distribution of charge. The most well-known example of this is the sodium-potassium pump, which transports three sodium ions out of the cell and two potassium ions into the cell. This creates a net positive charge outside the cell relative to the inside, thus establishing an electrochemical gradient and contributing to the membrane potential.

In contrast, channel proteins, carrier proteins, and cotransporters primarily facilitate the movement of molecules across the membrane but do not directly contribute to voltage generation. Channel proteins allow specific ions or molecules to passively flow through the membrane, while carrier proteins change shape to transport substances without creating a charge difference. Cotransporters work by coupling the transport of one substance with another, often using the energy from the electrochemical gradient established by electrogenic pumps, but they do not themselves generate a voltage across the membrane. Overall, the electrogenic pump is essential for establishing and maintaining the voltage across membranes in biological systems.