1 8/7/2015 Virus Structure & Classification developed by Hugh B. Fackrell

2 8/7/2015 Lecture Outline n Scope of virology n Nomenclature n Virion n Virus genome n Virus symmetry n Virion structure

3 8/7/2015 Scope of Virology n In developed countries viral infections are the most common cause of acute disease that does not require hospitalization n In developing countries viral infections are a common cause of mortality and disability especially among infants and children

4 8/7/2015 Viruses as a health hazard Now antibiotics effectively control most bacterial infections Viruses pose a relatively greater and less controlled threat to human health

5 8/7/2015 Virus n obligate intracellular parasite n delivers its genome into host cell –genome is either DNA or RNA n genome transcribed and translated by host synethetic machinary Viruses are NOT cellular

6 8/7/2015 Virus n submicroscopic particles –smallpox a large virus is at the limit of resolution of the light microscope –most require use of electrom microscope

7 8/7/2015 Viruses Infect All Life Forms n Bacteria>> bacteriophage n Plants n Fungi n Insects n Fish n Reptiles n Bird n Mammals

8 8/7/2015 Viral Nomenclature n viruse families end with -viridae –eg poxviridae retroviridae n Virus subfamilies -virinae –alphaherpesvirinae herpes simplex –gammaherpesvirinae- epstein Barr virus n Virus genera -virus –enterovirus- polio virus –lyssavirus -rabies virus

9 8/7/2015 Siglum n An abbreviation derived from a few or intial letters –(plural sigla)

10 8/7/2015 Virus Sigla n Respiratory Enteric and Orphan Viruses n Papilloma, Polyoma & Vacuolating agent Viruses n Hepatocytes & RNA genome

11 8/7/2015 Sigla (cont) n Parvovirus -small n Adenovirus - gland eg adenoid tissue n Herpes- creeping- nature of lesions n Toga virus - cloaked with envelope n Arena virus - sand like lesion n Corona virus- crown like peplomers n Bunya virus - Bunyamwera Africa n Calcivirus - cup like

12 8/7/2015 Herpes zoster

13 8/7/2015 Virion n A fully assembled infectious virus n At least two components n Genome –DNA or RNA –Single stranded or double stranded –Sense or antisense n Capsid –Protective protein coat

14 8/7/2015 DNA Viruses n Parvovirus ssDNA, sense or antisense, linear n HepadnaAvirus dsDNA,linear n Papovavirus dsDNA,circular n Adenovirus dsDNA,linear n Herpes virus dsDNA,linear n Pox virus dsDNA, linear

15 8/7/2015 RNA Viruses n ssRNA, Sense strand -picornavirus, calicivirus, togavirus, coronavirus n ssRNA, antisense strand -bunyavirus, orthomyxovirus, arenavirus, filovirus, rhabdovirus,paramyxovirus n Retrovirus ssRNA 2 copies n Reovirus dsRNA, segments

16 8/7/2015 Capsid n Protein coat that protects the genome n protection against nucleases n few structural proteins Capsids Self Assemble

17 8/7/2015 Virion Symmetry n Cubical Symmetry –Adenovirus –picorrnavirus n Helical Symmetry –Filovirus –Rhadovirus n Complex Symmetry –poxvirus –T4 bacteriophage

18 8/7/2015 Helical Symmetry n Helical rigid –Rhabdovirus,-rabies n Helical pleomorphic –Paramxyovirus -parainfluenza –,measles & respiratory syncytical virus –Orthomxyovirus -influenza

19 8/7/2015 Helical Symmetry

20 8/7/2015 Rhabdovirus

21 8/7/2015 Cubic Symmetry n Icosahedral Symmetry n 20 equilateral triangles n 12 vertices n 532 symmetry

22 8/7/2015 Icoshedral Structure

23 8/7/2015 Complex Symmetry n Very rigid, defined structures n may or may not have envelope

24 8/7/2015 Complex Symmetry

25 8/7/2015

26 8/7/2015 Polio Virus

27 8/7/2015 Peplomer n Glycoprotein spikes n on viral envelope n coded by viral genome n coronavirus,orthomyxovirus, arenavirus,Rhabdovirus,paramyxovirus Determine viral host range

28 8/7/2015 Viral Envelope n Some viruses are surrounded by an additional covering - viral envelope n derived from host cell membranes n contact virus proteins internally n glycosylated proteins externally 50% of animal viruses have an envelope