Editing Active transport (section)

==Primary active transport==

[[Image:Scheme sodium-potassium pump-en.svg|thumb|The action of the [[sodium-potassium pump]] is an example of primary active transport.]]
Primary active transport, also called direct active transport, directly uses metabolic energy to transport molecules across a membrane.<ref>{{cite book| title= Essentials of Human Physiology| first= Thomas M. |last= Nosek| chapter=Section 7/7ch05/7ch05p11 |chapter-url=http://humanphysiology.tuars.com/program/section7/7ch05/7ch05p11.htm |archive-url=https://web.archive.org/web/20160324124828/http://humanphysiology.tuars.com/program/section7/7ch05/7ch05p11.htm|archive-date=2016-03-24}}</ref> Substances that are transported across the cell membrane by primary active transport include metal ions, such as [[sodium|Na]]<sup>+</sup>, [[potassium|K]]<sup>+</sup>, [[magnesium|Mg]]<sup>2+</sup>, and [[calcium|Ca]]<sup>2+</sup>. These charged particles require [[Ion transporter|ion pump]]s or [[ion channel]]s to cross membranes and distribute through the body. {{cn|date=January 2025}}

Most of the [[enzyme]]s that perform this type of transport are transmembrane [[ATPase]]s. A primary ATPase universal to all animal life is the [[Na+/K+-ATPase|sodium-potassium pump]], which helps to maintain the [[Membrane potential|cell potential]]. The sodium-potassium pump maintains the membrane potential by moving three Na<sup>+</sup> ions out of the cell for every two<ref>{{Cite book|title=Tenth Edition, Campbell's Biology|last1=Reese|first1=Jane B.|last2=Urry|first2=Lisa A.|last3=Cain|first3=Michael L.|last4=Wasserman|first4=Steven A.|last5=Minorsky|first5=Peter V.|last6=Jackson|first6=Robert B.|publisher=Pearson Education Inc.|year=2014|isbn=978-0-321-77565-8|location=United States|pages=135|edition=Tenth}}</ref> K<sup>+</sup> ions moved into the cell. Other sources of energy for primary active transport are [[redox]] energy and [[photon]] energy ([[light]]). An example of primary active transport using redox energy is the mitochondrial [[electron transport chain]] that uses the reduction energy of [[NADH]] to move protons across the inner mitochondrial membrane against their concentration gradient. An example of primary active transport using light energy are the proteins involved in [[photosynthesis]] that use the energy of photons to create a proton gradient across the [[thylakoid membrane]] and also to create reduction power in the form of [[NADPH]]. {{cn|date=January 2025}}

===Model of active transport===

[[ATP hydrolysis]] is used to transport hydrogen ions against the [[electrochemical gradient]] (from low to high hydrogen ion concentration). [[Phosphorylation]] of the [[carrier protein]] and the binding of a [[hydrogen ion]] induce a conformational (shape) change that drives the hydrogen ions to transport against the electrochemical gradient. [[Hydrolysis]] of the bound [[phosphate group]] and release of hydrogen ion then restores the carrier to its original conformation.<ref>{{cite book|last=Cooper|first=Geoffrey|title=The Cell: A Molecular Approach|year=2009|publisher=ASK PRESS|location=Washington, DC|isbn=9780878933006|page=65}}</ref>