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'Active transport' (sometimes called 'active uptake') 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.

Contents

Process

Types

Relation to Cellular Energy

See also

References

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.

Types

★ 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 of the first solute.^[1]

Relation to Cellular Energy

Using conservative assumptions, it has been calculated that the amount of energy available to the cell is insufficient to power the estimated degree of active transport, e.g. by a factor of 15-30 times for the sodium pump alone ^[3]. Following vigorous debate in ''Science'' and elsewhere, this discrepancy has yet to be resolved. ^[4]

See also

★ Ion channel

★ Symporter

★ Antiporter

★ Passive transport

★ Osmosis

References

1.
2.
3. Ling, G.N. (1962). A physical theory of the living state: the association-induction hypothesis, Blaisdell Publ. Co., Waltham, Massachusetts.
4. Pollack, G.H. (2001). Cells, Gels and the Engines of Life, pp.17-18, Ebner and Sons Publ., Seattle.