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27 Cards in this Set
- Front
- Back
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What are viruses? what do they contain?
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-Obligatory intracellular parasites
-replicate by assembly -contain DNA or RNA (one or more segments) -Some are enclosed by an envelope -Some viruses have spikes or sophisticated structures |
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Host range
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-is determined by specific recognitions between host receptors and viral proteins and by cellular factors affect viral replication and spread among cells *tissue and cell specificity: cellular surface receptors
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Virus sizes
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24nm-3000nm
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Viron structure
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-Nucleic acid (DNA or RNA)
-Capsid (capsomeres) -Envelope -Spikes |
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3 types of viruses: Icosahedral virus, enveloped virus, and helical virus
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1) Icosahedral: 12 corners/ 20 sides/ 30 edges. Ex: Adenovirus
2) enveloped virus: Exs: Influenzavirus and Bovine Herpesvirus 3) Helical virus: long virus. Ex: Ebola virus |
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Complex viruses:Bacteriophage. Components and example
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They have a capsid (head), DNA, Sheath, tall fiber(legs), Baseplate(bottom), and pin(injection). Ex: Human Smallpox virus- orthopoxvirus
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Taxonomy of Viruses
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-Order(-virales)
-Family names end in (-viridae) -Genus names end in (-virus) -Viral Species: Common English names (Tobacco mosaic virus, Human immunodeficiency virus) -Subspecies are designated by a number or geographical origin |
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Baltimore Classification Scheme: by Genome and Replication Strategies Part I: dsDNA viruses, ssDNA viruses, and dsRNA viruses
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-dsDNA viruses: replicate through dsDNA
-ssDNA viruses: replicate through dsDNA intermediates -dsRNA viruses |
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Baltimore Classification Scheme: by Genome and Replication Strategies Part II: ssRNA viruses, ssRNA viruses, and Ambisense ssRNA viruses
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-ssRNA viruses: (+)-sense genomes
-ssRNA viruses: (-)-sense genomes -Ambisense ssRNA viruses: mosaics of +/- genomes |
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Baltimore Classification Scheme: by Genome and Replication Strategies Part III: Retroviruses and Pararetroviruses
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-Retroviruses: diploid ssRNA viruses replication via dsDNA
-Pararetroviruses: dsDNA viruses replication via ssRNA |
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Viral Infection Process: Entry
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STEP 1. Entry: dependent on all cell wall types.
-Animals: attachment to cell membrane, endocytosis, or fusion -Plants: wounds, insects -Bacteria: attachment to cell wall receptors or pili, injected or pulled into cells |
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Viral Infection Process: Uncoating
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STEP 2. Uncoating: removal of capsid to exposed nucleic acids
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Viral Infection Process: Biosynthesis: Gene expression/transcription
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STEP 3. Biosynthesis: Production of proteins and nucleic acids
-Gene expression (1st step for positive RNA viruses) -Transcription (1st step for DNA viruses and negative RNA viruses) |
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Viral Infection Process: Assembly
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STEP 4. Assembly: Nucleic acid and capsid proteins form virions
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Viral Infection Process: Release
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STEP 5. Release: by budding (enveloped viruses) or rupture or spreading to neighboring cells through plasmodesmata (plants)
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Attachment, penetration, uncoating
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By pinocytosis or by membrane fusion. (see slide for examples of both)
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dsDNA Viruses
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1) dsDNA genome enters into the nucleus
2) transcription of genes usually by host RNA polymerase 3) Semi-conservative replication of viral genomes by either host or viral DNA polymerase |
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ds DNA: Replication of DNA Virus steps 1-7
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1) Virion attaches to host cell
2) Virion enters cell, and its DNA is uncoated 3) A portion of viral DNA is transcribed, producing mRNA that encodes "early" viral proteins 4) Viral DNA is replicated and some viral proteins are made 5) Late translation: capsid proteins are synthesized. 6) Virions mature 7)Virions released |
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ssDNA Viruses
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-ssDNA first converted to dsRNA by host DNA polymerase
-Genes are expressed -A viral protein (Rep) initiate a rolling circle replication of the viral genome by a host DNA polymerase |
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dsRNA viruses
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-Carry a transcriptase (RNA-dependent RNA polymerase) in virions
-mRNA transcribes within the virion and then extruded for translation -Once all proteins and progeny viral RNA are made, and immature virion is formed, within which ssRNA is converted to dsRNA |
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dsRNA viruses replication steps 1-5
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1) attachment
2) Entry and uncoating 3) DNA replication by viral RNA-dependent RNA polymerase 4)Translation and synthesis of viral proteins 5)Maturation and release |
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(+) ssRNA Viruses
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-Genomic RNA is the same sense (+ sense) as mRNA, therefore translated DIRECTLY
-RdRp translated from genomic RNA -(+)-sense RNA copied to (-)-sense RNA (complementary RNA) -(-)-sense RNA serves as template to produce (+)-sense, genomic RNA |
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(+) ssRNA Virus replication steps 1-5
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1) Attachment
2) Entry and uncoating 3) RNA replication by viral RNA-dependent RNA polymerase 4) Translation and synthesis of viral proteins 5) Maturation and release |
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(-) strand and ambisense RNA viruses
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- (-)sense RNA viruses have a genome that is complementary to mRNA
-Ambisense RNA viruses have a mosaic genome of partial (+) or partial (-) sense RNA (ambiguous senses) -Viral genomic RNA cannot serve as messenger RNA, a virus must carry a transcritpase -Influenze viruses, Ebola virus, Hantavirus, Tomato spotted wilt virus |
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(-) Strand RNA virus Steps 1-5
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1) Attachment
2) Entry and uncoating 3) RNA replication by viral RNA-dependent RNA polymerase 4) Translation and synthesis of viral proteins 5) Maturation and release |
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Orthomyxoviridae
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Influenza A- Causes "epidemic influenza"
-An enveloped segmented (-) ssRNA virus -In nature, Influenze is a wild bird virus -There are human adapted strains but also, equine, swine, domestic bird(chicken) Flu strains -Influenze mutates rapidly, recombines frequently and sometimes jumps species |
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Retroviruses
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-Virions contain a "diploid" ssRNA genome
-Carry a reverse transcriptase -Upon infection, ssRNA is reverse-transcribes into dsDNA in cytoplasm -dsDNA transported into nucleus and integrated into host genome -Progeny viral RNA transcribes from the integrated provirus sequence -HIV, Human T-cell leukemia viruses |
