Editing Uniporter (section)

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[[Image:Porters.PNG|right|thumb|250px|Comparison of transport proteins]]

'''Uniporters,''' also known as '''solute carriers''' or '''facilitated transporters''', are a type of [[membrane transport protein]] that passively transports solutes (small molecules, ions, or other substances) across a cell membrane.<ref name="Zhang XC">{{cite journal |vauthors=Zhang XC, Han L |title=Uniporter substrate binding and transport: reformulating mechanistic questions |journal=Biophys Rep |volume=2 |issue=2–4 |pages=45–54 |date=2016 |pmid=28018963 |pmc=5138270 |doi=10.1007/s41048-016-0030-7 }}</ref>  It uses [[facilitated diffusion]] for the movement of solutes down their concentration gradient from an area of high concentration to an area of low concentration.<ref name="Alberts">{{cite book |first=Bruce |last=Alberts |title=Essential cell biology : an introduction to the molecular biology of the cell |publisher=Garland |oclc=36847771 |date=1998 |isbn=0-8153-2045-0 }}</ref> Unlike [[active transport]], it does not require energy in the form of [[Adenosine triphosphate|ATP]] to function. Uniporters are specialized to carry one specific ion or molecule and can be categorized as either channels or carriers.<ref>{{cite journal |vauthors=Wolfersberger MG |title=Uniporters, symporters and antiporters |journal=J Exp Biol |volume=196 |issue= |pages=5–6 |date=November 1994 |pmid=7823043 |doi=10.1242/jeb.196.1.5 }}</ref> Facilitated diffusion may occur through three mechanisms: uniport, symport, or antiport. The difference between each mechanism depends on the direction of transport, in which uniport is the only transport not coupled to the transport of another solute.<ref>{{cite book |vauthors=Pratt CA, Voet D, Voet JG |title=Fundamentals of biochemistry |publisher=Wiley |oclc=48137160 |date=2002 |isbn=0-471-41759-9 |pages=264–6 }}</ref>

Uniporter carrier proteins work by binding to one [[molecule]] or [[Substrate (biochemistry)|substrate]] at a time. Uniporter channels open in response to a stimulus and allow the free flow of specific molecules.<ref name="Alberts" />

There are several ways in which the opening of uniporter channels may be regulated:

# [[Voltage]] – Regulated by the difference in voltage across the membrane
# [[Stress (physics)|Stress]] – Regulated by physical [[pressure]] on the transporter (as in the [[cochlea]] of the [[ear]])
# [[Ligand]] – Regulated by the binding of a ligand to either the intracellular or extracellular side of the [[Cell (biology)|cell]]
Uniporters are found in [[Mitochondrion|mitochondria]], [[Cell membrane|plasma membranes]] and [[neuron]]s.The uniporter in the mitochondria is responsible for [[calcium]] uptake.<ref name="Zhang XC" /> The calcium channels are used for [[cell signaling]] and triggering [[apoptosis]]. The calcium uniporter transports calcium across the inner mitochondrial membrane and is activated when calcium rises above a certain concentration.<ref>{{Cite journal |last=Hoppe |first=U. |date=2010 |title=Mitochondrial Calcium Channels |journal=FEBS Letters |volume=584 |issue=10 |pages=1975–81 |doi=10.1016/j.febslet.2010.04.017 |pmid=20388514 |s2cid=33664763|doi-access=free |bibcode=2010FEBSL.584.1975H }}</ref> The [[CD98|amino acid transporters]] function in transporting neutral [[amino acid]]s for [[neurotransmitter]] production in brain cells.<ref name="Häfliger P" /> [[Voltage-gated potassium channel]]s are also uniporters found in neurons and are essential for [[action potential]]s.<ref>{{cite journal |vauthors=Kim DM, Nimigean CM |title=Voltage-Gated Potassium Channels: A Structural Examination of Selectivity and Gating |journal=Cold Spring Harb Perspect Biol |volume=8 |issue=5 |pages= a029231|date=May 2016 |pmid=27141052 |pmc=4852806 |doi=10.1101/cshperspect.a029231 }}</ref> This channel is activated by a voltage gradient created by [[Na+/K+-ATPase|sodium-potassium pumps]]. When the membrane reaches a certain voltage, the channels open, which [[Depolarization|depolarizes]] the membrane, leading to an [[action potential]] being sent down the membrane.<ref>{{Cite book |last=OpenStax College |title=Chapter 12.4 The Action Potential |publisher=OpenStax College |year=2013 |isbn=978-1938168130 |pages=523–531}}</ref> [[Glucose transporter]]s are found in the plasma membrane and play a role in transporting [[glucose]]. They help to bring glucose from the blood or extracellular space into cells usually to be utilized for metabolic processes in generating energy.<ref name="Olson AL" />

Uniporters are essential for certain physiological processes in cells, such as nutrient uptake, waste removal, and maintenance of ionic balance.