A uniport is a type of transponder protein which only allows a single molecule to pass through the cell membrane at any one time. This occurs along the electrochemical gradient of the molecule in question on either side of the membrane.
Function of the uniport protein
The uniport proteins are partly responsible for facilitated diffusion of solutes across cell and organelle membranes.
The various types of facilitated diffusion transporter proteins. M is a section through the cell membrane. A uniport protein is shown in I. © Zoph, Wikimedia CC by-sa 3.0