Editing Active transport (section)

==Background==
Specialized [[transmembrane protein]]s recognize the [[Chemical substance|substance]] and allow it to move across the membrane when it otherwise would not, either because the [[phospholipid bilayer]] of the membrane is impermeable to the substance moved or because the substance is moved against the direction of its [[concentration gradient]].<ref>{{usurped|1=[https://web.archive.org/web/20120120234037/http://www.buzzle.com/articles/active-transport-process.html Active Transport Process]}}. Buzzle.com (2010-05-14). Retrieved on 2011-12-05.</ref> There are two forms of active transport, primary active transport and secondary active transport. In primary active transport, the proteins involved are pumps that normally use chemical energy in the form of ATP. Secondary active transport, however, makes use of potential energy, which is usually derived through exploitation of an [[electrochemical]] gradient. The energy created from one ion moving down its electrochemical gradient is used to power the transport of another ion moving against its electrochemical gradient.<ref name="ncbi.nlm.nih.gov">Lodish H, Berk A, Zipursky SL, et al. Molecular Cell Biology. 4th edition. New York: W. H. Freeman; 2000. Section 15.6, [https://www.ncbi.nlm.nih.gov/books/NBK21687/ Cotransport by Symporters and Antiporters].</ref> This involves pore-forming [[proteins]] that form channels across the [[cell membrane]]. The difference between passive transport and active transport is that the active transport requires energy, and moves substances against their respective concentration gradient, whereas passive transport requires no cellular energy and moves substances in the direction of their respective concentration gradient.<ref>Lodish H, Berk A, Zipursky SL, et al. Molecular Cell Biology. 4th edition. New York: W. H. Freeman; 2000. Chapter 15, [https://www.ncbi.nlm.nih.gov/books/NBK21525/ Transport across Cell Membranes].</ref>

In an [[antiporter]], one substrate is transported in one direction across the membrane while another is [[cotransport]]ed in the opposite direction.  In a [[symporter]], two substrates are transported in the same direction across the membrane. Antiport and symport processes are associated with [[secondary active transport]], meaning that one of the two substances is transported against its concentration gradient, utilizing the energy derived from the transport of another ion (mostly Na{{Sup|+}}, K{{Sup|+}} or H{{Sup|+}} ions) down its concentration gradient. {{cn|date=January 2025}}

If substrate molecules are moving from areas of lower concentration to areas of higher concentration<ref>[http://www.biologycorner.com/bio1/active.html Active Transport] {{webarchive |url=https://web.archive.org/web/20110824003030/http://www.biologycorner.com/bio1/active.html |date=August 24, 2011 }}. Biologycorner.com. Retrieved on 2011-12-05.</ref> (i.e., in the opposite direction as, or ''against'' the concentration gradient), specific transmembrane carrier proteins are required. These proteins have receptors that bind to specific molecules (e.g., [[Sodium-glucose transport proteins|glucose]]) and transport them across the cell membrane. Because energy is required in this process, it is known as 'active' transport. Examples of active transport include the transportation of [[sodium]] out of the cell and [[potassium]] into the cell by the sodium-potassium pump. Active transport often takes place in the internal lining of the [[small intestine]].

Plants need to absorb mineral salts from the soil or other sources, but these salts exist in very dilute [[Solution (chemistry)|solution]]. Active transport enables these cells to take up salts from this dilute solution against the direction of the [[concentration gradient]]. For example, [[chloride]] (Cl<sup>−</sup>) and [[nitrate]] (NO<sub>3</sub><sup>−</sup>) ions exist in the cytosol of plant cells, and need to be transported into the vacuole. While the vacuole has channels for these ions, transportation of them is against the concentration gradient, and thus movement of these ions is driven by hydrogen pumps, or proton pumps.<ref name="ncbi.nlm.nih.gov"/>