Editing Capsid (section)

===Helical===
[[File:Helical capsid with RNA.png|thumb|left|3D model of a helical capsid structure of a virus]]

Many rod-shaped and filamentous plant viruses have capsids with [[Symmetry (geometry)#Helical symmetry|helical symmetry]].<ref name="autogenerated9">{{cite journal | vauthors = Yamada S, Matsuzawa T, Yamada K, Yoshioka S, Ono S, Hishinuma T | title = Modified inversion recovery method for nuclear magnetic resonance imaging | journal = The Science Reports of the Research Institutes, Tohoku University. Ser. C, Medicine. Tohoku Daigaku | volume = 33 | issue = 1–4 | pages = 9–15 | date = December 1986 | pmid = 3629216 }}</ref> The helical structure can be described as a set of ''n'' 1-D molecular helices related by an ''n''-fold axial symmetry.<ref name="autogenerated84"/> The helical transformation are classified into two categories: one-dimensional and two-dimensional helical systems.<ref name="autogenerated84">{{cite journal | vauthors = Aldrich RA | title = Children in cities--Seattle's KidsPlace program | journal = Acta Paediatrica Japonica | volume = 29 | issue = 1 | pages = 84–90 | date = February 1987 | pmid = 3144854 | doi = 10.1111/j.1442-200x.1987.tb00013.x | s2cid = 33065417 }}</ref> Creating an entire helical structure relies on a set of translational and rotational matrices which are coded in the protein data bank.<ref name="autogenerated84"/> Helical symmetry is given by the formula ''P''&nbsp;=&nbsp;''μ''&nbsp;x&nbsp;''ρ'', where ''μ'' is the number of structural units per turn of the helix, ''ρ'' is the axial rise per unit and ''P'' is the pitch of the helix.  The structure is said to be open due to the characteristic that any volume can be enclosed by varying the length of the helix.<ref name="virology">{{cite book | vauthors = Racaniello VR, Enquist LW |title=Principles of Virology, Vol. 1: Molecular Biology |publisher=ASM Press |location=Washington, D.C. |year=2008 |isbn=978-1-55581-479-3 }}</ref> The most understood helical virus is the tobacco mosaic virus.<ref name="autogenerated9"/> The virus is a single molecule of (+) strand RNA.  Each coat protein on the interior of the helix binds three nucleotides of the RNA genome. Influenza A viruses differ by comprising multiple ribonucleoproteins, the viral NP protein organizes the RNA into a helical structure.  The size is also different; the tobacco mosaic virus has a 16.33 protein subunits per helical turn,<ref name="autogenerated9"/> while the influenza A virus has a 28 amino acid tail loop.<ref>{{cite journal|vauthors=Ye Q, Guu TS, Mata DA, Kuo RL, Smith B, Krug RM, Tao YJ|date=26 December 2012|title=Biochemical and structural evidence in support of a coherent model for the formation of the double-helical influenza A virus ribonucleoprotein|journal=mBio|volume=4|issue=1|pages=e00467–12|doi=10.1128/mBio.00467-12|pmc=3531806|pmid=23269829}}</ref>