Direct Active Transport
- The carrier proteins span the plasma membrane and bind to the molecule or ion being transported.
- The molecule binds to the receptor sites on the carrier protein.
- The ATP binds to the protein causing it to split into ADP and a phosphate molecule. This causes the protein to change shape and it opens at the other end to let the molecule out.
- The molecule is now released on to the other side of the membrane.
- The phosphate molecule is also released and the protein reverts back to it's original shape and the phosphate molecule recombines with the ADP to form ATP.
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Active transport needs ATP because it goes against a concentrated gradient.
Facilitated diffusion occurs down a concetrated gradient and so does not need metabolic energy to help it do so.
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