Icosahedral Symmetry:• Most economical way to build

symmetric shell, maximal internal volume, with nonsymmetric proteins: icosahedron

• Icosahedron: solid with 20 faces, each an equilateral triangle, approximates a sphere

• Icosadeltahedral capsids• Found in larger viruses• Shape similar to a soccer

ball

Helical Symmetry:

• Less defined shape or structure

• Rod-shaped capsomers directly coat the nucleic acid

• Assemble into helical nucleocapsid

• ALL human viruses with this capsid type are enveloped

Name the capsid type:

AdenovirusIcosadeltahedral capsid

EbolaHelical capsid

PoxvirusComplex capsid

Note: Images are not to scale

Poliovirusicosaheral capsid

• Range in size from 24-200 nm in length

• Contain a head structure, which can vary in size and shape

• The head encloses nucleic acid and acts as the protective covering

• Some phages have tails attached to the phage head

• At the end of the tail, phages like T4 have a base plate and one or more tail fibers attached to it.

Bacteriophage

Significance of phages include:

• Carry virulence factors for certain bacteria• Essential members of the ecosystem• Contributions to understanding genetics and molecular

biology• Phage as Tools

Potential applications for bacteriophages in human health