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:9/18/2014)... are the ideal animal in which to study the ... ocean into tens of thousands of freshwater streams and ... to adapt to the new environment. , Breeding studies ... turned up one of the genes that controls tooth ... gene,s regulation in a freshwater population is associated with ...
(Date:9/17/2014)... creation of the Santa Ana Wildfire Threat Index ... of the powerful, hot, dry Santa Ana wind, which ... was introduced Sept. 17 by the U.S. Forest Service, ... Electric. , The index includes four classification levels ranging ... help fire agencies and other emergency responders, the media ...
(Date:9/17/2014)... USA -- "Nature has developed, very cleverly, some lessons ... in optical design," said Joseph Shaw, director of the ... explore surfaces and structures at the nanoscale, we,ll discover ... San Diego in August during a conference called "The ... and Rongguang Liang of the University of Arizona College ...
Breaking Biology News(10 mins):Counting fish teeth reveals regulatory DNA changes behind rapid evolution, adaptation 2Counting fish teeth reveals regulatory DNA changes behind rapid evolution, adaptation 3UCLA scientists play key role in developing new Santa Ana Wildfire Threat Index 2Nature's designs inspire research into new light-based technologies 2Nature's designs inspire research into new light-based technologies 3
... LA Research led by Lauren Cole, a public ... of Public Health and Director of the Epidemiology Program ... the incidence of head and neck cancer has risen ... with the greatest increase among middle-aged white men. At ...
... gene called XRCC2 cause increased breast cancer risk, according to ... Human Genetics . The study looked at families that have ... in the currently known breast cancer susceptibility genes. Sean ... professor in the Department of Oncological Sciences at the University ...
... such as the Iberian lynx, are under an increasingly serious ... that can even survive in extremely arid environments. A study ... to adapt according to climate. The life cycle of ... patterns of people and goods. These parasites and the pathogens ...
Cached Biology News:LSUHSC research finds HPV-related head & neck cancers rising, highest in middle-aged white men 2A new breast cancer susceptibility gene 2Ticks can adapt to the Spain's climatic diversity 2
Other biology definitionOther Tags