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Disease
- Term coined by Pasteur to describe the spoilage of beer and wine
- A virus is a disease-causing agent
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Discovery of Virus
- Pasteur 1884(rabies)
- Mayer 1886(Tobacco Mosaic Virus)
- Could not isolate the disease-causing agent by means used for bacteria
- Disease-agent could not be killed by EtOH
- Could not be cultured in media that supports bacterial growth*
- Could only proliferate in growing tissue
- NOT BACTERIA!
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Viruses
- The term virus (Latin for poisonous substance) was used to describe a disease-causing substance that is not a bacteria
- Fundamentally different from cellular forms of life
- The first virus ever seen - Tobacco Mosaic Virus (1935)
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Viruses Characteristics
- Genetic material in a protein coat
- Naked
- enveloped
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Viruses: Genetic Material
- ssRNA, dsRNA, ss cDNA, ss DNA, ds DNA, ds cDNA.
- Living things are double stranded DNA all the time
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Viruses:
Obligate Parasites
- Must be inside host cell to reproduce
- Lack all metabolic machinery: ribosomes, most enzymes
- Hijack host’s metabolism
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Viruses: Host Specificity
- Host range
- Plant
- Bacterial (bacteriophage (bacteria eater); phage)
- Animal
- Specificity based on “fit” between viral proteins and host receptors
- 3D specificity
- Plant and Bacterial are naked. Animal are almost always enveloped. This looks just like our cells so they fit right in.
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Viruses: Mode of Infection
- Infection: entry into host cell
- Mechanisms vary:
- Phage inject NA
- Receptor-mediated endocytosis
- Facilitated diffusion
- Active transport
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Viruses: Capable of Self-Assembly
- Take over host’s resources and machinery
- To make viral proteins (capsid) and nucleic acids
- Self-assembly
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Viruses Characteristics (Distinction)
- Each virus is distinct in:
- Nucleic acid
- Capsid structure
- Host range
- Mode of infection
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Viruses: General information
- Infectious particles: nucleic acid in a protein coat
- Naked or enveloped
- Obligate parasites
- Host range
- Mode of infection
- Capable of self-assembly
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Viruses are non-living
- Cell theory: cell is smallest unit of life
- Viruses are acellular (do not have cells)
- Lack all cellular machinery
- Cannot replicate outside a host
- Do not ALWAYS have their genetic material in the form of ds DNA
- Do not have all the characteristics of living things
Organization, metabolism, homeostasis, grow/develop/reproduce, adapt, evolve. If you can’t say yes to every single one, you are not a living thing.
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+/- strand
- (+)strand: coding
- (-)strand: noncoding
- (-) strand viral RNA must first be copied [(+) strand] before it can be translated
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Growing Viruses
- Phage:
- Plaque method
- Animal viruses
- In animals
- In eggs
- Cell culture
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Cytopathic Effects of Selected Viruses
- Cytocidal (cell death)
- Acidophilic inclusion bodies in nucleus
- Basophilic inclusion bodies in nucleus
- Acidophilic inclusion in cytoplasm
- Cell fusion
- Transformation
- Destruction of T cells
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Viral Replication
- Viruses can only replicate inside a host cell
- Usually follow a one-step growth curve
eclipse period, virus released from host, acute infection, death
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