Virus Architecture and Nomenclature
• Robert YL Wang (王永樑)
• Email: [email protected]
• http://memo.cgu.edu.tw/ylwang/
This is a molecular model of a Simian Virus 40 particle. It is a
naked virus that was first identified as a contaminant of rhesus
monkey kidney cells being used to produce a vaccine against
poliovirus during the 1960s.
 Mimivirus: the largest know virus
400 nM particle; 1181 kb (nt); 1262 ORFs
The arrow points to a Mimivirus particle infecting an amoeba.
 The limits of microscopic and human eye
resolution
• Scale and
microscope
limitations
 Virus Properties
• Protection (phosphodiester bond)
• Recognition (capsid)
• Self-assembly
• Fidelity
• Economy
Adapted from Prescott, L. M., Harley, J. P., and Klein, D. A. Microbiology, Sixth
Edition. McGraw-Hill Higher Education, 2005.
Why Are Virus Particles Formed?
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Protection
Recognition
Self-Assembly
Fidelity
Economy
Electron micrograph of purified poliovirus particles
 Electron micrograph and molecular model of an adenovirus.
 Molecular model of adenovirus.
 Virus Structure and Morphology
• Stability
• Two Types of Viral Shapes
– Icosahedral
– Helical
Schematic drawing of a typical icosahedral-shaped
virus particle
Schematic drawing of a typical helical-shaped virus
particle
Electron Micrographs of Virus Examples
Icosahedral Symmetry
• Build a 3-dimensional naked, icosahedral shaped virus
• Other shapes
– Complex
Schematic drawing of a complex-shaped poxvirus particle.
– Electron micrograph of a single brick-shaped or complex-shaped
smallpox particle.
 Enveloped Virus Particles
A typical enveloped helical-shaped virus particle.
A typical enveloped icosahedral-shaped virus particle.
 Viruses that Challenge the Definition of a Virus
• Giruses
– Not filterable through
“sterilizing” filters
– Nucleo-Cytoplasmic
Large DNA Viruses
• Mimivirus
• Mamavirus
• Virophages
– Sputnik
• ORFan genes
Structure of the Mimivirus particle
Table. Virion Sizes and Shapes of Selected Families of
Viruses
Table cont.
 Baltimore Classification
• Created by David Baltimore
• Seven classes
– Viruses grouped by type of nucleic acids they
possess and its replication scheme.
– Figure 3-15
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I.
II.
III.
IV.
V.
VI.
VII.
dsDNA viruses
ssDNA viruses
dsRNA viruses
+ssRNA viruses
–ssRNA viruses
RNA reverse transcribing viruses
DNA reverse transcribing viruses
Table. Genome Properties of Selected DNA
Virus Families
Table. Genome Properties of Selected RNA
Virus Families
 Taxonomy: What’s in a Name?
• Definition of viruses
• Use of porcelain Chamberland filter
• Electron microscopy
Courtesy Dr. Ng Mah Lee, Mary, Department of Microbiology, National
University of Singapore
Scanning electron micrograph of SARS associated
coronaviruses (SARS-CoV)
Table. Examples of the Origins of Virus Names
 The International Committee on Taxonomy
of Viruses (ICTV)
• Charged with developing a universal taxonomic scheme
to name and classify viruses
• ICTV database
• Based on physical and chemical properties.
– Order (-virales)
– Family (-viridae)
– Subfamily (-virinae)
– Genus (-virus)
– Common names
Table. Examples of the Origins of Virus Names
Additional Hierarchical Levels and Definitions
• Species
– Polythetic class
• Type-species
• Strain
• Variant
 Compilation of viral diversity
Specialty Groups and Collections
• WHO Collaborating Centers for Reference and
Research on Influenza
• WHO Food and Agricultural Organization of the United
Nations
• American Type Culture Collection (ATCC)
Viral Disease Syndromes Overlap
Virus File 3-1:
The Race to Characterize SARS-CoV
• Atypical pneumonia in Hanoi,
Vietnam
• Carlo Urbani
• Assistance of WHO
• SARS-CoV spread by air travel