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Secondary active transport.
Secondary active transport. Click for higher resolution image.
Secondary active transport.
Secondary active transport is a form of active transport across a biological membrane in which a transporter protein couples the movement of an ion (typically Na+ or H+) down its electrochemical gradient to the uphill movement of another molecule or ion against a concentration/electrochemical gradient. Thus, energy stored in the electrochemical gradient of an ion is used to drive the transport of another solute against a concentration or electrochemical gradient. The ion moving down its electrochemical gradient is referred to as the driving ion because it is movement of this ion that drives the uphill movement of another ion/molecule (driven ion/molecule). Secondary active transport is also commonly referred to as ion-coupled transport. Unlike in primary active transport in which ATP hydrolysis provides the free energy needed to move solutes against a concentration or electrochemical gradient, in secondary active transport, the free energy needed to perform active transport is provided by the concentration gradient of the driving ion. Two types of secondary active transport processes exist: cotransport (also known as symport) and exchange (also known as antiport). In cotransport, the direction of transport is the same for both the driving ion and driven molecule/ion, whereas in exchange, the driving ion and driven ion/molecule are transported in opposite directions. X and Y represent transporter substrates. Na+, sodium; K+, potassium; ATP, adenosine triphosphate; ADP, adenosine diphosphate; Pi, inorganic phosphate.

See also:
Secondary Active Transport (in Lecture Notes)






Posted: Saturday, April 2, 2016
Last updated: Sunday, April 3, 2016