Co-transport
Encyclopedia
Co-transport, also known as coupled transport or secondary active transport
, refers to the simultaneous or sequential passive transfer of molecule
s or ion
s across biological membrane
s in a fixed ratio. Permitting one ion or molecule to move from the side where it is more concentrated to that where it is less concentrated increases entropy
and can serve as a source of energy
for metabolism
(e.g. in ATP synthase
). In cotransporters, it is used to force the transport of another ion or molecule (usually) from the side where it is less concentrated to that where it is more concentrated. Cotransporters can be classified as symporter
s and antiporter
s depending on whether the substances move in the same or opposite directions .
presented for the first time his discovery of the sodium-glucose cotransport as the mechanism for intestinal glucose absorption. Crane
's discovery of cotransport was the first ever proposal of flux coupling in biology.
Secondary active transport
In secondary active transport or co-transport, uses energy to transport molecules across a membrane; however, in contrast to primary active transport, there is no direct coupling of ATP; instead, the electrochemical potential difference created by pumping ions out of the cell is used...
, refers to the simultaneous or sequential passive transfer of molecule
Molecule
A molecule is an electrically neutral group of at least two atoms held together by covalent chemical bonds. Molecules are distinguished from ions by their electrical charge...
s or ion
Ion
An ion is an atom or molecule in which the total number of electrons is not equal to the total number of protons, giving it a net positive or negative electrical charge. The name was given by physicist Michael Faraday for the substances that allow a current to pass between electrodes in a...
s across biological membrane
Biological membrane
A biological membrane or biomembrane is an enclosing or separatingmembrane that acts as a selective barrier, within or around a cell. It consists of a lipid bilayer with embedded proteins that may constitute close to 50% of membrane content...
s in a fixed ratio. Permitting one ion or molecule to move from the side where it is more concentrated to that where it is less concentrated increases entropy
Entropy
Entropy is a thermodynamic property that can be used to determine the energy available for useful work in a thermodynamic process, such as in energy conversion devices, engines, or machines. Such devices can only be driven by convertible energy, and have a theoretical maximum efficiency when...
and can serve as a source of energy
Energy
In physics, energy is an indirectly observed quantity. It is often understood as the ability a physical system has to do work on other physical systems...
for metabolism
Metabolism
Metabolism is the set of chemical reactions that happen in the cells of living organisms to sustain life. These processes allow organisms to grow and reproduce, maintain their structures, and respond to their environments. Metabolism is usually divided into two categories...
(e.g. in ATP synthase
ATP synthase
right|thumb|300px|Molecular model of ATP synthase by X-ray diffraction methodATP synthase is an important enzyme that provides energy for the cell to use through the synthesis of adenosine triphosphate . ATP is the most commonly used "energy currency" of cells from most organisms...
). In cotransporters, it is used to force the transport of another ion or molecule (usually) from the side where it is less concentrated to that where it is more concentrated. Cotransporters can be classified as symporter
Symporter
A cotransporter is an integral membrane protein that is involved in secondary active transport. It works by binding to two molecules or ions at a time and using the gradient of one solute's concentration to force the other molecule or ion against its gradient....
s and antiporter
Antiporter
An antiporter is an integral membrane protein involved in secondary active transport of two or more different molecules or ions across a phospholipid membrane such as the plasma membrane in opposite directions.In secondary active transport, one species of solute moves along its electrochemical...
s depending on whether the substances move in the same or opposite directions .
Discovery of cotransport
In August 1960, in Prague, Robert K. CraneRobert K. Crane
Robert Kellogg Crane is an American biochemist best known for his discovery of sodium-glucose cotransport.-Biography:...
presented for the first time his discovery of the sodium-glucose cotransport as the mechanism for intestinal glucose absorption. Crane
Robert K. Crane
Robert Kellogg Crane is an American biochemist best known for his discovery of sodium-glucose cotransport.-Biography:...
's discovery of cotransport was the first ever proposal of flux coupling in biology.
See also
- Cotransporter
- SymporterSymporterA cotransporter is an integral membrane protein that is involved in secondary active transport. It works by binding to two molecules or ions at a time and using the gradient of one solute's concentration to force the other molecule or ion against its gradient....
- Sodium/phosphate cotransporterSodium/phosphate cotransporterThe sodium/phosphate cotransporter is a protein found in the proximal tubule of the nephron. It is responsible for reabsorbing phosphate that has been filtered out at the glomerulus.-See also:* Renal physiology* Cotransporter...
- Sodium-glucose transport proteinsSodium-glucose transport proteinsSodium-dependent glucose cotransporters are a family of glucose transporter found in the intestinal mucosa of the small intestine and the proximal tubule of the nephron . They contribute to renal glucose reabsorption...
- Glucose transporterGlucose transporterGlucose transporters are a wide group of membrane proteins that facilitate the transport of glucose over a plasma membrane. Because glucose is a vital source of energy for all life these transporters are present in all phyla...