13-a Viruses pp H1N1

2 Viruses Size, Structure, Morphology Taxonomy Growth Identification

3 SMALL size One type of nucleic acid, either DNA or RNA Protein coat, surrounds the NA Few or no enzymes of their own Characteristics of Viruses Obligate intracellular parasite

4 Multiply inside living host cells by using synthesizing machinery of the cell Proteins, generate ATP Specialized structures to transfer viral NA to other cells Inert Outside Living Host Cells Significant for development of antiviral drugs Because most drugs would also interfere with functioning of host cell = toxic

5 1. Protein coat (capsids) Capsomeres (make up capsids) The number varies The types of protein very 2. Nucleic acids 3. Size 4. Morphology Can’t use biochemical tests or disease symptoms as for classification Criteria used to ‘Classify’ Viruses A virion contains:

6 Figure 13.1 Sizes

7 Viral Structure Nucleic acids –DNA or RNA is –Either single or double stranded –Linear or circular –In segments Example: influenza virus

8 Capsid – Protein coat protects nucleic acid Capsomere –Each capsid composed of protein subunits –Arrangement of capsomeres is characteristic of a particular type of virus Envelope (on some viruses) –Covers the capsid Spikes –CHO-protein, project from envelope surface for attachment

9 1.Helical 2.Polyhedral 3.Enveloped 4.Complex ‘Group’ into several different morphological types Viral Morphology …based on their capsid architecture

Long rods Rigid / flexible NA in center Diseases: –Ebola hemorrhagic fever –Rabies 10 Helical Fig. 13.4a, b

Non-enveloped ‘many sided,’ 20 ‘faces’ Icosahedron Diseases: –Adenovirus –Poliovirus 11 Polyhedral Fig. 13.2

Covered Roughly spherical Enveloped helical Enveloped polyhedral Spikes Diseases: –Influenza (EH) –Herpes simples (EP) –Flu, fever blisters, chickenpox, shingles, mononucleosis 12 Enveloped Fig. 13.3

Bacteriophage Capsids with additional structures Head contains NA Tail sheath, fibers, plate, pin Diseases: –Infect bacteria 13 Complex – 1 Fig. 13.5

Poxvirus No clearly identifiable capsids Have several coats NA inside the coats Disease: –Smallpox 14 Complex – 2 Fig. 13.5

15 Viral Taxonomy NamesEnding Family-viridae Genus-virus Viral speciesCommon names are used for species SubspeciesDesignated by a number Viral species: A group of viruses sharing the same genetic information and ecological niche (host)

16 Taxonomy Examples NamesEnding FamilyHerpesviridae GenusSimplexvirus NamesEnding FamilyRetroviridae GenusLentivirus SpeciesHuman Immunodeficiency Virus SubspeciesHIV-1, HIV-2

1.Provide living cells 2.Viruses that infect bacteria useful for understanding growth 3.Pathogenic viruses difficult to cultivate 1.Can’t use bacteriological media 2.Bacteriophages infect bacteria and grow cultures on plates 3.Grow only in higher primates & humans –Use animal cell culture techniques Viral Growth

18 Bacteriophages form plaques on a lawn of bacteria –It’s a virus that infects bacteria –Plaque is a ‘clearing’ in the bacterial ‘lawn’ –Count, PFU’s –PFU: plaque forming units Fig Bacteriophage

19 Animal viruses grown in living animals or in embryonated eggs Vaccine production Figure 13.7 Viral Growth in Living Cells

20 Animal and plant viruses grown in cell culture Figure 13.8 Viral Growth in Cell Culture –Continuous animal cell lines maintained indefinitely –Famous cell line: HeLa

21 Viral Identification – Not Easy 1.Too small to see 2.Western blotting 3.Virus kills host cell 4.Restriction fragment length polymorphism 5.Polymerase chain reaction 1.Observe with electron microscope 2.Serological methods 3.Cytopathic effects 4.RFLP’s 5.PCR

22 Uninfected (mo) cellsInfected (mo) cells, 24 hrs later Figure 13.9 Cytopathic effect (CPE): a visible effect on a host cell, may result in host cell death; ‘host’ cells deteriorate Viral Identification – Cytopathic Effect

23 Q: 1.Which of the following statements is NOT true? a.Viruses contain DNA or RNA b.The nucleic acid of a virus is surrounded by a protein coat c.Viruses multiply inside living cells using viral mRNA, tRNA and ribosomes d.Viruses cause the synthesis of specialized infectious elements e.Viruses multiply inside living cells

24 Q: 1. In which of the following ways do viruses differ from bacteria? a.Viruses are filterable b.Viruses are obligate intracellular parasites c.Viruses don’t have any nucleic acid d.Viruses are not composed of cells e.All of the above 2. Virus spikes are used for attachment to the host cell. True False

25 Q: 1. What type of cell is the virus, seen in the figure, capable of infecting? a.A liver cell b.A plant cell c.A bacterial cell d.Many different cell types 2. Viruses range in size from nm in length and are easy to see in a compound light microscope. True False