Navigation Links
Active transport


Active transport is the mediated transport of biochemicals, and other atomic/molecular substances, across membranes. Unlike passive transport, this process requires chemical energy. In this form of transport, molecules move against either an electrical or concentration gradient (collectively termed an electrochemical gradient). This is achieved by either altering the affinity of the binding site or altering the rate at which the protein changes conformations.

Contents

Types

There are two main types, primary and secondary. In primary transport energy is directly coupled to movement of desired substance across a membrane, independent of any other species. Secondary transport concerns the diffusion of one species across a membrane to drive the transport of another.

Primary

Primary active transport directly uses energy to transport molecules across a membrane. Most of the enzymes that perform this type of transport are transmembrane ATPases. A primary ATPase universal to all cellular life is the sodium-potassium pump, which helps maintain the cell potential.

Secondary

In secondary active transport, there is no direct coupling of ATP; instead, the electrochemical potential difference created by pumping ions out of cells is used. The two main forms of this are counter-transport (antiport) and co-transport (symport).

Counter-transport

In counter-transport two species of ion or other solute are pumped in opposite directions across a membrane. One of these species is allowed to flow from high to low concentration, which yields the entropic energy to drive the transport of the other solute from a low concentration region to a high one. An example is the sodium-calcium exchanger or antiporter, which allows three sodium ions into the cell to transport one calcium out.

Many cells also posses a calcium ATPase, which can operate at lower intracellular concentrations of calcium and sets the normal or resting concentration of this important second messenger. But the ATPase exports calcium ions more slowly: only 30 per second versus 2000 per second by the exchanger. The exchanger comes into service when the calcium concentration rises steeply or "spikes" and enables rapid recovery. This shows that a single type of ion can be transported by several enzymes, which need not be active all the time (constitutively), but may exist to meet specific, intermittent needs.

Co-transport

Co-transport also uses the flow of one solute species from high to low concentration to move another molecule against its preferred direction of flow; but here, both solutes move in the same direction across the membrane. An example is the glucose symporter, which cotransports two sodiums for every molecule of glucose it imports into the cell.

See also


'"/>


(Date:12/11/2014)... blood pressure plays a role in human health has been ... for high blood pressure – was first described as a ... used in measuring blood pressure was invented in 1896. ... its triggers and its effects. In fact, recent findings have ...
(Date:12/10/2014)... YORK , Dec. 8, 2014 You,ve been here before: ... can,t remember your password, site key or the answer to your ... teacher? Today, Hoyos Labs , a digital ... put an end to the frustration that comes with usernames, passwords ...
(Date:12/10/2014)... 2014  Wake Forest Baptist Medical Center today announced plans for ... Funding for this $50 million capital project is part of ... summer. The medical education building will be ... complex, adjacent to 525@vine in Wake Forest Innovation Quarter. Construction ...
Breaking Biology News(10 mins):Research points to need for new approaches to treatment of high blood pressure 2Research points to need for new approaches to treatment of high blood pressure 3Research points to need for new approaches to treatment of high blood pressure 4The Password is Finally Dead: Launch of 1U Mobile App Eliminates Need for All Usernames and Passwords 2The Password is Finally Dead: Launch of 1U Mobile App Eliminates Need for All Usernames and Passwords 3Wake Forest Baptist to Build New Medical Education Facility In Wake Forest Innovation Quarter 2Wake Forest Baptist to Build New Medical Education Facility In Wake Forest Innovation Quarter 3Wake Forest Baptist to Build New Medical Education Facility In Wake Forest Innovation Quarter 4
... of researchers from the Department of Biochemistry and Molecular ... Autònoma de Barcelona has discovered that tetanus toxin, which ... against psychological disorders such as depression, anxiety and anorexia, ... as Parkinson's disease. , Tetanus toxin is a neurotoxin ...
... grain sorghum , Trials have begun in Kansas on ... of many plastics, drugs, solvents and food additives. Developed ... form of the bacteria E. coli that metabolizes glucose ... to make key chemical intermediates like succinate is a ...
... scientist from the University of Manchester has discovered the first ... up to 20 million years old. , Two droplets of ... amber which also contains the spider - Filistatidae - a ... The droplets are the first identified examples of spider blood ...
Cached Biology News:Tetanus toxin found to have therapeutic properties 2Bacteria are key to 'green' plastics, drugs 2Bacteria are key to 'green' plastics, drugs 3Spider blood found in 20 million year old fossil 2
Other biology definitionOther Tags