Membrane transport

Membrane transport occurs through the use of membrane transport proteins. Without these, membranes would only be permeable to some gases and small, water soluble molecules.  ATP-powered pumps use energy from ATP hydrolysis in order to move ions or molecules against their concentration gradient, whereas Ion channels allow movement of ions through the membrane down their concentration gradient. Transporters are split into three groups; Uniporters, which transport a single molecule down a concentration gradient, Symporters, which transport a molecule against its concentration gradient through the transport of other molecules down their electrochemical gradient (same direction of travel across membrane), and Antiporters, which also use the transport of other molecules down their electrochemical gradient to transport other molecules (opposite directions of travel of molecules across the membrane).