Certain molecules and ions are not able to pass through cell membranes to balance the concentration gradient. Transport proteins are required to support this process of facilitated transport. Facilitated transport does not require energy. Examples are shown in the upper part of the graphic. A uniporter transports one small molecule in one direction (glucose transporter or proton transporter). Symporters allow entrance of 2 molecules in the same direction (glucose-sodium uptake). Antiporters regulate the passage of 2 molecules in opposite direction (sodium-calcium antiporter).
Transport of certain