Editing Spider silk (section)

===Structural===
[[File:Structure of spider silk thread Modified.svg|thumb|310x310px| Spider silk structure: crystalline beta-sheets separated by amorphous linkages]]

Silks have a hierarchical structure. The [[primary structure]] is the [[amino acid]] sequence of its proteins ([[spidroin]]), mainly consisting of highly repetitive [[glycine]] and [[alanine]] blocks,<ref name="Hinman 92">{{cite journal |author= Hinman, M. B.|author2= Lewis, R. V.|name-list-style= amp |date= 1992 |title= Isolation of a clone encoding a second dragline silk fibroin. Nephila clavipes dragline silk is a two-protein fiber |journal= J. Biol. Chem. |volume= 267 |pages= 19320–24 |pmid= 1527052 |issue= 27|doi= 10.1016/S0021-9258(18)41777-2|doi-access= free }}</ref><ref name="Simmons 96">{{cite journal |author= Simmons, A. H.|author2= Michal, C. A.|author3= Jelinski, L. W.|name-list-style= amp |date= 1996 |title= Molecular orientation and two-component nature of the crystalline fraction of spider dragline silk |journal= Science |volume= 271 |pages= 84–87 |doi= 10.1126/science.271.5245.84 |issue=5245 |pmid= 8539605|bibcode = 1996Sci...271...84S |s2cid= 40043335}}</ref> which is why silks are often referred to as a [[Copolymer|block co-polymer]]. On a secondary level, the short side-chained alanine is mainly found in the crystalline domains ([[beta sheet]]s) of the nanofibril. Glycine is mostly found in the so-called amorphous matrix consisting of helical and beta turn structures.<ref name="Simmons 96" /><ref name="van Beek 02">{{cite journal |author= van Beek, J. D.|author2= Hess, S.|author3= Vollrath, F.|author4= Meier, B. H.|name-list-style= amp |date= 2002 |title= The molecular structure of spider dragline silk: Folding and orientation of the protein backbone |journal= Proc. Natl. Acad. Sci. U.S.A. |volume= 99 |pages= 10266–71 |doi= 10.1073/pnas.152162299 |issue= 16 |pmid= 12149440 |pmc= 124902|bibcode = 2002PNAS...9910266V |doi-access= free}}</ref> The interplay between the hard crystalline segments and the strained elastic semi-amorphous regions gives spider silk its extraordinary properties.<ref>{{cite journal |author= Liu, Y.|author2= Sponner, A.|author3= Porter, D.|author4= Vollrath, F. |date= 2008 |title=Proline and Processing of Spider Silks |journal=[[Biomacromolecules]] |volume=9 |pages=116–21 |doi=10.1021/bm700877g |pmid= 18052126 |issue= 1}}</ref><ref>{{cite journal|author= Papadopoulos, P.|author2= Ene, R.|author3= Weidner, I.|author4= Kremer, F. |date= 2009 |title=Similarities in the Structural Organization of Major and Minor Ampullate Spider Silk |journal=[[Macromolecular Rapid Communications|Macromol. Rapid Commun.]] |volume=30 |pages=851–57 |doi=10.1002/marc.200900018|pmid= 21706668|issue= 9–10}}</ref> Various compounds other than protein are used to enhance the fibre's properties. [[Pyrrolidine]] has [[Hygroscopy|hygroscopic]] properties that keep the silk moist while warding off ant invasion. It occurs in high concentration in glue threads. [[Potassium hydrogen phosphate]] releases [[Hydron (chemistry)|hydrogen ions]] in aqueous solution, resulting in a [[pH]] of about 4, making the silk [[acid]]ic and thus protecting it from [[fungi]] and [[bacteria]] that would otherwise digest the protein. [[Potassium nitrate]] is believed to prevent the protein from denaturing in the acidic milieu.<ref name="Heimer">Heimer, S. (1988). Wunderbare Welt der Spinnen. ''Urania''. p. 12</ref>

Termonia introduced this first basic model of silk in 1994.<ref name="Termonia 94">{{cite journal |author= Termonia, Y. |date= 1994 |title= Molecular Modeling of Spider Silk Elasticity |journal= Macromolecules |volume= 27 |pages= 7378–81 |doi=10.1021/ma00103a018 |issue= 25 |bibcode = 1994MaMol..27.7378T }}</ref> He suggested [[Crystallite|crystallites]] embedded in an amorphous matrix interlinked with [[Hydrogen bond|hydrogen bonds]]. Refinements to this model include: semi-crystalline regions were found<ref name="Simmons 96" /> as well as a fibrillar skin core model suggested for spider silk,<ref>{{cite journal |author= Vollrath, F.|author2= Holtet, T.|author3= Thogersen, H. C.|author4= Frische, S.|name-list-style= amp |date= 1996 |title= Structural organization of spider silk |journal= [[Proceedings of the Royal Society B]] |volume= 263 |pages= 147–51 |doi=10.1098/rspb.1996.0023 |issue= 1367 |bibcode= 1996RSPSB.263..147V|s2cid= 136879037}}</ref> later visualised by [[Atomic Force Microscopy|AFM]] and [[Transmission Electron Microscopy|TEM]].<ref>{{cite journal |author= Sponner, A.|date= 2007 |title= Composition and hierarchical organization of a spider silk |journal= PLOS ONE|volume=2 |pages= e998 |doi= 10.1371/journal.pone.0000998 |issue= 10 |pmid= 17912375 |pmc= 1994588 |bibcode = 2007PLoSO...2..998S |editor1-last= Scheibel |editor1-first= Thomas |first2= Wolfram |first3= Shamci |first4= Eberhard |first5= Frank |first6= Klaus |last2= Vater, Wolfram |last3= Monajembashi, Shamci |last4= Unger, Eberhard |last5= Grosse, Frank |last6= Weisshart, Klaus |doi-access= free }} {{open access}}</ref> Sizes of the nanofibrillar structure and the crystalline and semi-crystalline regions were revealed by [[neutron scattering]].<ref>{{cite journal |author= Sapede, D.|date= 2005 |title= Nanofibrillar structure and molecular mobility in spider dragline silk |journal=  Macromolecules|volume= 34 |page= 623 |doi=10.1021/ma0507995 |bibcode = 2005MaMol..38.8447S |first2= T. |last3= Forsyth |first3= V. T. |last4= Koza |first4= M. M. |last5= Schweins |first5= R. |last6= Vollrath |first6= F. |last7= Riekel |first7= C. |issue= 20 |last2= Seydel }}</ref>

The fibres' microstructural information and macroscopic mechanical properties are related.<ref name="plaza 12">{{cite journal |author= Plaza, G.R.|author2= Pérez-Rigueiro, J.|author3= Riekel, C.|author4= Perea, G.B.|author5= Agulló-Rueda, F.|author6= Burghammer, M.|author7=  Guinea, G.V.|author8= Elices, M.|date= 2012 |title= Relationship between microstructure and mechanical properties in spider silk fibers: identification of two regimes in the microstructural changes |journal= Soft Matter |volume=8 |pages= 6015–26 |doi= 10.1039/C2SM25446H |issue= 22|bibcode= 2012SMat....8.6015P|url= https://zenodo.org/record/897750}}</ref> Ordered regions (i) mainly reorient by deformation for low-stretched fibres and (ii) the fraction of ordered regions increases progressively for higher fibre stretching.<br /><gallery widths="900" heights="400">
File:0.Figure.png|Schematic of the spider's orb web, structural modules, and spider silk structure.<ref>{{Cite journal|last1=Zhao|first1=Yue|last2=Hien|first2=Khuat Thi Thu|last3=Mizutani|first3=Goro|last4=Rutt|first4=Harvey N.|date=June 2017|title=Second-order nonlinear optical microscopy of spider silk|journal=Applied Physics B|volume=123|issue=6|pages=188|arxiv=1706.03186|doi=10.1007/s00340-017-6766-z|bibcode=2017ApPhB.123..188Z|s2cid=51684427}}</ref> On the left is shown a schematic drawing of an orb web. The red lines represent the dragline, radial line, and frame lines. The blue lines represent the spiral line, and the centre of the orb web is called the "hub". Sticky balls drawn in blue are made at equal intervals on the spiral line with viscous material secreted from the aggregate gland. Attachment cement secreted from the piriform gland is used to connect and fix different lines. Microscopically, the spider silk secondary structure is formed of spidroin with the structure shown on the right side. In the dragline and radial line, a crystalline β-sheet and an amorphous helical structure are interwoven. The large amount of β-spiral structure gives elastic properties to the capture part of the orb web. In the structural modules diagram, a microscopic structure of dragline and radial lines is shown, composed mainly of two proteins of MaSp1 and MaSp2, as shown in the upper central part. The spiral line has no crystalline β-sheet region.
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