1 Virus Structure Classification developed by Hugh B
1 Virus Structure & Classification developed by Hugh B. Fackrell 10/25/2020
2 Lecture Outline Scope of virology n Nomenclature n Virion n Virus genome n Virus symmetry n Virion structure n 10/25/2020
3 Scope of Virology 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 n 10/25/2020
4 Viruses as a health hazard Now antibiotics effectively control most bacterial infections Viruses pose a relatively greater and less controlled threat to human health 10/25/2020
5 Virus obligate intracellular parasite n delivers its genome into host cell n – genome is either DNA or RNA n genome transcribed and translated by host synthetic machinery Viruses are NOT cellular 10/25/2020
6 Virus n submicroscopic particles – smallpox a large virus is at the limit of resolution of the light microscope – most require use of electron microscope 10/25/2020
7 Viruses Infect All Life Forms Bacteria>> bacteriophage n Plants n Fungi n Insects n Fish n Reptiles n Bird n Mammals n 10/25/2020
8 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 10/25/2020
9 Siglum n An abbreviation derived from a few or intial letters – (plural sigla) 10/25/2020
10 Virus Sigla Respiratory Enteric and Orphan Viruses n Papilloma, Polyoma & Vacuolating agent Viruses n Hepatocytes & RNA genome n 10/25/2020
11 Sigla (cont) 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 n 10/25/2020
12 Herpes zoster 10/25/2020
13 Virion A fully assembled infectious virus n At least two components n Genome n – DNA or RNA – Single stranded or doublr stranded – Sense or antisense n Capsid – Protective protein coat 10/25/2020
14 DNA Viruses Parvovirus ss. DNA, sense or antisense, linear n Hepadna. Avirus ds. DNA, linear n Papovavirus ds. DNA, circular n Adenovirus ds. DNA, linear n Herpes virus ds. DNA, linear n Pox virus ds. DNA, linear n 10/25/2020
15 RNA Viruses ss. RNA, Sense strand -picornavirus, calicivirus, togavirus, coronavirus n ss. RNA, antisense strand -bunyavirus, orthomyxovirus, arenavirus, filovirus, rhabdovirus, paramyxovirus n Retrovirus ss. RNA 2 copies n Reovirus ds. RNA, 10 -12 segments n 10/25/2020
16 Capsid Protein coat that protects the genome n protection against nucleases n few structural proteins n Capsids Self Assemble 10/25/2020
17 Virion Symmetry n Cubical Symmetry – Adenovirus – picorrnavirus n Helical Symmetry – Filovirus – Rhadovirus n Complex Symmetry – poxvirus – T 4 bacteriophage 10/25/2020
18 Helical Symmetry n Helical rigid – Rhabdovirus, -rabies n Helical pleomorphic – Paramxyovirus -parainfluenza – , measles & respiratory syncytical virus – Orthomxyovirus -influenza 10/25/2020
19 Helical Symmetry 10/25/2020
20 Rhabdovirus 10/25/2020
21 Cubic Symmetry Icosahedral Symmetry n 20 equilateral triangles n 12 vertices n 532 symmetry n 10/25/2020
22 Icoshedral Structure 10/25/2020
23 Complex Symmetry Very rigid, defined structures n may or may not have envelope n 10/25/2020
24 Complex Symmetry 10/25/2020
25 10/25/2020
26 Polio Virus 10/25/2020
27 Peplomer Glycoprotein spikes n on viral envelope n coded by viral genome n coronavirus, orthomyxovirus, arenavirus, Rhabdovirus, paramyxovirus n Determine viral host range 10/25/2020
28 Viral Envelope 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 n 50% of animal viruses have an envelope 10/25/2020
- Slides: 28