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ATP is used to:
- directly move molecules
individually move molecules using a concentration gradient.
- individually move molecules using a concentration gradient which has already been set up by active transport (co-transport).
1) Metabolic energy in the form of ATP is needed.
2) Substances are moved against a concentration gradient, low to high.
3) Carrier protein molecules act as 'pumps'.
4) The process is very selective, with specific substances being transported.
1) The carrier protein span the plasma membrane and bind to the molecule or ion to be transported on one side.
2) The molecule or ion binds to receptor sites on the carrier protein.
3) On the inside of the cell, ATP binds to the protein causing it to split into ADP and a phosphate molecule. Due to this the protein molecule changes shape and opens to the opposite side of the membrane.
4) The molecule or ion is then released to the other side of the membrane.
5) The phosphate molecules is released from the protein which causes the protein to revert to its original shape, ready for the process to be repeated. The phosphate molecule recombines with the ADP to form ATP during respiration.
Sometimes more than one molecule or ion may be moved in the same direction t the same time by active transport. Occasionally, the molecules or ions are moved into a cell/organelle at the same time.
Here, the sodium ions are actively removed from the cell/organelle while potassium ions are actively taken in from the surroundings. This process is important to an number of processes, including the secretion of the nerve impulse.
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