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