Active transport of molecules through the membranes of a cell requires a supply of ATP to provide the energy necessary to move the molecules against a concentration gradient. The sodium/potassium pump shown in the animation consists of a trans-membrane protein to which potassium and sodium ions attach. When they are attached, an ATP molecule will be used to cause the protein to deform and flip through the phospholipid membrane and then release the attached ions. As the ions are released the protein will flip again to return to its original position. It can then pick up more ions to transfer. Active transport pumps for glucose and amino acids also occur in cell membranes.