4.4 Active transport
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What is active transport
. The movement of molecules or ions into or out of a cell from a region of lower concentration to a region of higher concentration using ATP.
What is ATP used for in active transport
. Directly move molecules . Individually move molecules using a concentration gradient which has already been set up by active transport. This is known as co-transport
How does active transport differ from forms of passive transport
. Metabolic energy in the form of ATP is required for it . Substances are moved AGAINST a concentration gradient, so from low to high . Carrier proteins which act as ‘pumps’ are involved . The process is very selective, with specific substances being transported
Describe the process of active transport of a single molecule or ion
. The carrier proteins span the plasma membrane and bind to one side of the molecule or ion to be transported . The molecule or ion binds to receptor sites on the carrier protein . On the inside of the cell/organelle, ATP binds to protein causing it to split into ADP and a phosphate molecule. As a result the protein molecule changes shape and opens to the opposite side of the membrane . The phosphate molecule is then released from the protein which causes the protein to revert to its original shape, ready for the process to be repeated. The phosphate molecule then recombines with the ADP to make ATP during respiration.
Differences and similarities between active transport and facilitated diffusion
Similarities: - Both use carrier proteins Differences: . Facilitated diffusion occurs down the concentration gradient whilst active transport goes against concentration gradient. . So this means that facilitated diffusion doesn’t require metabolic energy (ATP) whilst active transport does.
How many molecules/ions can be moved in the same direction during active transport
. More than one can be moved in the same direction at the same time
What happens with the sodium-potassium pump
Occasionally, a molecule/ion can be moved into the cell whilst another is being removed out of the cell. An example of this is the sodium-potassium pump. . Sodium ions are actively removed from the cell or organelle whilst potassium ions are actively taken in from the surroundings . This process is essential to the number of important processes in an organism eg the creation of nerve impulses.