SCIENCE PHOTO LIBRARY SCIENCE PHOTO LIBRARY
Active membrane transport. Illustration of the mechanism of primary active transport across a cell membrane (phospholipid bilayer, blue). Here, a dissolved molecule (solute) of calcium (Ca2+ ion) is being moved through a membrane channel (orange) against the natural electrochemical gradient. The energy for this ion transport comes from hydrolysis of molecules of ATP (adenosine triphosphate). The calcium ion is shown attached to the ATP enzyme ATPase. For this artwork without labels, see image C023/8776.
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