Icosahedral Symmetry Most economical way to build symmetric

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: Ebola Helical capsid Adenovirus Icosadeltahedral capsid Note: Images are not to scale Poliovirus icosaheral capsid Poxvirus Complex capsid

Bacteriophage • 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 T 4 have a base plate and one or more tail fibers attached to it.

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