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14 Cards in this Set
- Front
- Back
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What is a virus? |
Very small Infectious Obligate intracellular parasite Virus particles (virions) are not living They're an assemblage of chemicals and cannot replicate Virus replication dependent on infection of a cellular host Cannot generate ATP No known viruses contain ribosomes Some viruses have RNA genomes, only organisms known to have such Some viruses have single stranded genomes, even the RNA genomed viruses
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Virus ultra structure basics |
Virus coats come in either: Spheres , rods or a combination of the two The coats are made from subunits called Capsomer Some viruses are membrane bound, they take it from their host cell |
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Virus ultrastructure: Symmetry |
All viruses have rotation around axis Rod viruses have helical symmetry Spherical viruses have Icosahedral symmetry
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Different types of viral genomes? |
1) DNA, single or double 2) RNA, single or double 3)Use both dna and rna, dependent on stage of replication cycle Example: Retrovirus, Genome replicates via DNA intermediate Use reverse transcription to translate their RNA to DNA in host cell (Using enzyme: reverse transciptase) |
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What is common to all viruses? |
They all need to make mRNA |
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General properties of viruses, Extracellular? |
In their extracellular state = Virion Contains some form of nucleic acid Surrounded by protein capsule, and other components Metabolically inert Has to be stable enough to live out host cell |
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General properties of viruses, Intracellular?
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Virus replication is dependent on host cell metabolism Virus redirects existing host cell machinery Virions produced in late stages of infection |
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General structure of a virion? |
1) Nucleic acid always surrounded by capsid capsid is protein coat or shell 2) Capsid composition: structural subunits (capsomers) Can be more than one protein type in capsomer or, several proteins composed into capsomer |
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Naked and enveloped virions |
Virions are either naked or enveloped The envelope consists of host membrane and often other virus specific protiens |
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Features of helical symmetry |
length of capsule determined by length of genome width determined by size and packing of subunits |
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Features of icosahedral symmetry |
20 faces most efficient type of packing in a closed shell formed of 12 pentons |
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Bacteriophage features |
Bacteriophages have a icosahedral head and a helical tail, with tail fibres they infect bacteria only they carry enzymes used to break through PG cell wall |
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basics of virus repliction cycle |
the virus needs to induce the host cell to synthesise all virion components 1) Attachment / adsorbtion to receptors on host 2) Penetration/ entry (endocytosis) 3) Uncoating of capsule, to exposed nucleic acids 4) Synthesis of new nucleic acid and proteins 5) Assembly of structural subunits and packaging of genome into new virions 6) Release of mature virions from host |
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One step growth curve of virus's infecting cell, |
1) Eclipse, coat and nucleic acid separation 2) Latent period, replication of nucleic acids and proteins 3) Maturation, number of active virions increases 4) Assembly and release 5) Release from cells number of cells released called 'burst size,' |
