icosahedral

Examples of icosahedral in the following topics:

• Complex and Asymmetrical Virus Particles

  • While some have symmetrical shapes, viruses with asymmetrical structures are referred to as "complex. " These viruses possess a capsid that is neither purely helical nor purely icosahedral, and may possess extra structures such as protein tails or a complex outer walls.
  • Some bacteriophages, such as Enterobacteria phage T4 , have a complex structure consisting of an icosahedral head bound to a helical tail, which may have a hexagonal base plate with protruding protein tail fibers.
  • The capsid appears hexagonal under an electron microscope, therefore the capsid is probably icosahedral.
  • Although it has an icosahedral head, its tail makes it asymmetrical, or complex in terms of structure.

• Virus Classification

  • Capsids are classified as naked icosahedral, enveloped icosahedral, enveloped helical, naked helical, and complex .
  • The adenovirus has an icosahedral capsid .
  • Viruses can also be classified by the design of their capsids which are classified as naked icosahedral, enveloped icosahedral, enveloped helical, naked helical, and complex.
  • Adenovirus (left) is depicted with a double-stranded DNA genome enclosed in an icosahedral capsid that is 90–100 nm across.
  • The capsid of the (a) polio virus is naked icosahedral; (b) the Epstein-Barr virus capsid is enveloped icosahedral; (c) the mumps virus capsid is an enveloped helix; (d) the tobacco mosaic virus capsid is naked helical; and (e) the herpesvirus capsid is complex.

• General Morphology

  • Icosahedral - Most animal viruses are icosahedral or near-spherical with icosahedral symmetry.
  • Complex - These viruses possess a capsid that is neither purely helical nor purely icosahedral, and that may possess extra structures such as protein tails or a complex outer wall.

• Viruses of Archaea

  • Other morphologies have also been described including spindle shaped, rod shaped, filamentous, icosahedral, and spherical.
  • Bacteriophages (viruses infecting bacteria) belonging to the families Tectiviridae and Corticoviridae have a lipid bilayer membrane inside the icosahedral protein capsid and the membrane surrounds the genome.
  • The crenarchaeal virus Sulfolobus turreted icosahedral virus has a similar structure.

• Double-Stranded DNA Viruses: Adenoviruses

  • Adenoviruses are non-enveloped, icosahedral DNA viruses which cause upper respiratory infections, primarily in children.
  • Adenoviruses are medium-sized (90–100 nm), non-enveloped, icosahedral viruses composed of a nucleocapsid and a linear, double-stranded DNA (dsDNA) genome.

• Mu: A Double-Stranded Transposable DNA Bacteriophage

  • It belongs to the family Myoviridae , and consists of an icosahedral head, a contractile tail, and six tail fibers.

• Nature of the Virion

  • Many virions are spheroidal—actually icosahedral (the capsid having 20 triangular faces)—with regularly arranged units called capsomeres, two to five or more along each side.

• Viral Size

  • Shapes of viruses are predominantly of two kinds: rods, or filaments, so called because of the linear array of the nucleic acid and the protein subunits; and spheres, which are actually 20-sided (icosahedral) polygons.

• Temperate Bacteriophages: Lambda and P1

  • P1 has an icosahedral "head" containing the DNA, attached to a contractile tail with six tail fibers.
  • It has an icosahedral head containing the genome attached at one vertex to the tail.

• Single-Stranded DNA Bacteriophages

  • They also possess 'mushroom-like' protrusions positioned at the three-fold axes of symmetry of their icosahedral capsids.
  • Microviridae are non-enveloped and round with an icosahedral symmetry.