Editing Liquid crystal (section)

==Biological liquid crystals==
Lyotropic liquid-crystalline phases are abundant in living systems, the study of which is referred to as [[lipid polymorphism]]. Accordingly, lyotropic liquid crystals attract particular attention in the field of biomimetic chemistry. In particular, [[biological membrane]]s and [[cell membranes]] are a form of liquid crystal. Their constituent molecules (e.g. [[phospholipid]]s) are perpendicular to the membrane surface, yet the membrane is flexible.<ref name="Templer Seddon 1991">{{cite news |last1=Templer |first1=Richard |last2=Seddon |first2=John |title=The World of Liquid Crystals |url=https://www.newscientist.com/article/mg13017695-400-the-world-of-liquid-crystals/ |access-date=15 December 2023 |work=[[New Scientist]] |date=18 May 1991 |quote=You might be surprised to find out that cell membranes are liquid crystals. In fact, the first recorded observations of the liquid crystalline phase were of myelin, the material that coats nerve fibres. |archive-date=December 15, 2023 |archive-url=https://web.archive.org/web/20231215151806/https://www.newscientist.com/article/mg13017695-400-the-world-of-liquid-crystals/ |url-status=live }}</ref> These lipids vary in shape (see page on [[lipid polymorphism]]). The constituent molecules can inter-mingle easily, but tend not to leave the membrane due to the high energy requirement of this process. Lipid molecules can flip from one side of the membrane to the other, this process being catalyzed by [[flippase]]s and floppases (depending on the direction of movement). These liquid crystal membrane phases can also host important proteins such as receptors freely "floating" inside, or partly outside, the membrane, e.g. CTP:phosphocholine cytidylyltransferase (CCT).

Many other biological structures exhibit liquid-crystal behavior. For instance, the concentrated [[protein]] solution that is extruded by a spider to generate [[spider silk|silk]] is, in fact, a liquid crystal phase. The precise ordering of molecules in silk is critical to its renowned strength. [[DNA]] and many [[peptide|polypeptides]], including actively-driven cytoskeletal filaments,<ref>{{cite journal|author6-link=Hartmut Löwen| vauthors = Wensink HH, Dunkel J, Heidenreich S, Drescher K, Goldstein RE, Löwen H, Yeomans JM | title = Meso-scale turbulence in living fluids | journal = Proceedings of the National Academy of Sciences of the United States of America | volume = 109 | issue = 36 | pages = 14308–13 | date = September 2012 | pmc = 3607014 | doi = 10.1073/pnas.1215368110 | pmid = 22908244 | bibcode = 2013PNAS..110.4488S | doi-access = free }}</ref> can also form liquid crystal phases. Monolayers of elongated cells have also been described to exhibit liquid-crystal behavior, and the associated topological defects have been associated with biological consequences, including cell death and extrusion.<ref>{{cite journal | vauthors = Saw TB, Doostmohammadi A, Nier V, Kocgozlu L, Thampi S, Toyama Y, Marcq P, Lim CT, Yeomans JM, Ladoux B | display-authors = 6 | title = Topological defects in epithelia govern cell death and extrusion | journal = Nature | volume = 544 | issue = 7649 | pages = 212–216 | date = April 2017 | pmid = 28406198 | pmc = 5439518 | doi = 10.1038/nature21718 | bibcode = 2017Natur.544..212S }}</ref> Together, these biological applications of liquid crystals form an important part of current academic research.