eukaryotes and viruses
DESCRIPTION
Eukaryotes and Viruses. Chapters 12 and 13. Viral Characteristics and Structure. Why Viruses aren’t Alive. General Characteristics of Viruses. Name derives from the Latin for “poison” Obligatory intracellular parasites Referred to as filterable Contain a single type of nucleic material - PowerPoint PPT PresentationTRANSCRIPT
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Eukaryotes and Viruses
Chapters 12 and 13
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Viral Characteristics and Structure
Why Viruses aren’t Alive
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General Characteristics of Viruses
• Name derives from the Latin for “poison”
• Obligatory intracellular parasites• Referred to as filterable• Contain a single type of nucleic
material• The nucleic material is covered in a
protein coat.• Use the synthesis machinery of the
host to multiply.
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Why are they not Alive?• No independent metabolism or
reproduction• No single phylogenetic origin• No cellular structure• No ribosomes
• Though they DO evolve and reproduce.
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Host Range• Viruses have a specific subset of cell types
they will infect, referred to as Host Range.• Most viruses can only infect a single
species• Some viruses can cross species barriers• Numerous factors influence host range
• Viruses that infect bacteria are referred to as bacteriophage or simply phage.
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Viral Particle Size
Staphylococcus Bacteria1 μm in diameter
Poxviridae
Lentiviruses
Picornaviridae
Bacteriophage
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Viral Structure• A Virion is a complete, infectious viral
particle and is composed of…– Nucleic Acid– Capsid and Envelope
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Nucleic Acid• Only a single type of nucleic acid
(RNA or DNA) is present in any species of virus.
• Unlike cellular life, viral nucleic acid can be either single or double-stranded (again only a single type per species)
• Size of the genetic structure can range from a few thousand base pairs to a quarter of a million
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Capsid and Envelope• Capsids are regular repeating protein
structures composed of capsomeres.• Some viral species also have a host-
derived envelope surrounding the capsid
• Some viral species have protein/ carbohydrate “spikes” rising from the surface that can be used for identification
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Viral Morphology
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Viral Taxonomy
How do you do a taxonomy of something that isn’t alive?
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Viral Taxonomy• Without a shared phylogeny there is no use for
the higher taxons (Domain, Kingdom, Phylum, and Class)
• Typically viral species are referred to by Order, Family, Genus and a descriptive common name (in place of a species epithet)
• Based on – Nucleic Acid type– Strategy of replication– Morphology– Host range
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Viral Replication
No, not 1 becomes 2, more like 1 becomes 1000.
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Growing Bacteriophage
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Growing Animal Viruses
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Viral Identification• Polyphasic Identification–Morphology– Detection of Antibodies–Western Blotting of known viral proteins– Nucleic Methodologies• PCR• RFLP• RNA PCR
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Lytic Bacteriophage Cycle
Attachment
Penetration
Biosynthesis Maturation
Release
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Lysogenic Bacteriophage Cycle
Lytic Cycle
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Animal Unenveloped DNA Viral Replication
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DNA vs. RNA Viral Replication
• There are various types of RNA viruses.• Replication of the Genetic Material can be
simple or a multistep process.– +RNA, direct translation and replication by viral
protein– -RNA, indirect translation and replication by viral
protein– dsRNA, direct translation and relication by viral
protein– Retroviruses, conversion of RNA to DNA,
integration and then production by host.
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ComparisonBacteriophage• Attachment to Cell
Wall proteins.• Viral DNA is injected
into cell• No removal of capsid
required• Biosynthesis in
cytoplasm• Lysogeny• Host cell lysed for
release
Animal• Attachment to plasma
membrane proteins and glycoproteins.
• Capsid enters cells• Capsid removed by
enzymes• Biosynthesis in nucleus or
cytoplasm• Latency• Enveloped viruses bud and
nonenveloped rupture.
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Viruses and Cancer
One of many factors
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Oncogenic Viruses• Some viruses and known to help trigger
cancers, called oncogenic viruses.• These viruses affect oncogenes, natural
parts of our genetic structure that can cause cancer.
• The process of becoming cancerous is termed transformation.
• Oncogenic Viruses integrate into the host genetic material.
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Known Oncogenic VirusesType of Virus Viral Species Associated Cancer
DNA Human Papillomavirus Cervical Cancer
Epstein-Barr Virus Burkitt’s Lymphoma
Hepatitis B Virus Liver Cancer
Kaposi Sarcoma-Associated Hepervirus
Kaposi Sarcoma
Merkel Cell Polyomavirus Merkel Cell Carcinoma
RNA Human T-Lymphotropic Virus 1 Leukemia
Hepatitis C Virus Liver Cancer
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Latency, Persistence and the Prions
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Acute, Latent, and Persistent Viral Infections
• Acute Infections are those that cause immediate proliferation.
• Latent infections can occur by itself or after an acute infection, where the viral load remains undetected for a long period of time before reemerging quickly.
• Persistent Infections are ones where the viral load build over a long period of time.
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Graph of Acute, Latent and Persistent Viral Infections
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Prions• Prions are infectious protein particles• Prions are altered forms of a normal protein
in the host that can catalyze the alteration of other “normal” protein particles to the “prion” state
• They cause neurological degradation and death with no known treatment.
• Since each prion protein is infectious, they are extremely resistant to control measures.
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Prion Reaction
PrPC + PrPSc 2 PrPSc