Active transport
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Active transport is the mediated transport of biochemicals, and other atomic/molecular substances, across membranes. Unlike passive transport, this process requires the expenditure of cellular energy to move molecules "uphill" against a gradient.
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[edit] Process
In this form of transport, molecules move against either an electrical or concentration gradient (collectively termed an electrochemical gradient).
- The active transport of small molecules or ions across a cell membrane is generally carried out by transport proteins that are found in the membrane.
- Larger molecules such as starch can also be actively transported across the cell membrane by processes known as endocytosis and exocytosis.
- Particles that are moved through a membrane from a region of low concentration to high is known as active transport.
[edit] Types
There are two main types: primary active transport and secondary active transport.
- In primary transport, energy from hydrolysis of ATP is directly coupled to the movement of a specific substance across a membrane independent of any other species.[1]
- In secondary active transport, the required energy is derived from energy stored in the form of concentration differences in a second solute. Typically, the concentration gradient of the second solute was created by primary active transport, and the diffusion of the second solute across the membrane drives secondary active transport.[2]
[edit] See also
[edit] References
Membrane transport
Passive transport: Diffusion - Facilitated diffusion - Osmosis
Active transport: Primary active transport - Secondary active transport
