Ch 27.1 and 27.2 By: Dom Carter and Matt McKay

Viruses Viruses aren’t cells Has a basic structure with a core nucleic acid surrounded by a protein Lacks a cytoplasm Viruses contain only a single nucleic acid, either DNA or RNA

Structure of virions There are 4 structures, helical, icosahedral, binal, or polymorphic

Viruses replicate by taking over host machinery A cell with a virus is often damaged by infection Viruses can reproduce only when they enter cells When viruses are outside the cell, viral particles are called virions and are metabocaly inert.

Continued… Viruses lack ribosomes and the enzymes necessary for protein synthesis Viruses hijack the transcription and translation systems to produce the viral proteins from early genomes.

Most viruses come in two simple shapes Most viruses are either helical or icosahedral Helical viruses have a rodlike or threadlike appearance Icosahedral have a soccer ball shape Icosahedron is a structure with 20 equilateral triangular facets

Icosahedral virion Poliovirus has icosahedral symmetry