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Types of viral classification
Classical system, disease-based classification, Baltimore system
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Principal cause of common cold
Rhinovirus, Family: Picornaviridae, Genus: Enteroviruses
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Picornaviridae
RNA viruses, infect gastrointestinal tract, spread to other areas of body (nervous system)
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Virion
Complete viral particle
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Capsid:
Proteins of the shell, protect genome from damage, is pseudo-stable (needs to be stable outside of the cell and able to release genetic material outside cell). very specific/highly evolved proteins
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Many viral capsids have ___
Repeating patterns, because there is not room for many proteins
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Common viral capsid structures
- Helical: Sheet rolled up
- Icosahedral: made up of only a few types of proteins, looks like d20 generally
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Use of X-ray crystallography in virology
Visualizing viral proteins
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Simple viruses usually have what kind of capsid?
A simple repetitive one.
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Reasons to study DNA viruses
- Disease (antivirals and vaccines)
- Vectors for foreign gene expression
- Models for regulation of gene expression
- Models for oncogenesis
- Models for latency
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Permissive Host
an organism/cells that permit completion of a viral multiplication cycle
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Non-Permissive Host
A host that does not permit completion of a viral multiplication cycle. Infection does not occur: host lacks some required factor/anti-viral mechanism
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Productive Infection
Results in production of infectious virus progeny. Infected host may survive
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Abortive Infection
Viral infection is initiated but stalls/is terminated. Host usually survives
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Inapparent infection
Low level infection wherein virus-specific multiplication is difficult to detect and symptoms are absent or inapparent to the host.
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Chronic Infection
Condition in which virus is present and multiplying. The host is a constant source of infectious virus
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Latent Infection
Virus goes dormant but can alternate between periods of active multiplication. Reactivation from latency can result in disease and shedding of infectious virus.
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Most human DNA virus can cause:
Latent infections
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How do Small and Large DNA viruses differ in gene expression
- Small viruses express early genes all at same time and late genes all at same time
- Large viruses express immediate early genes (regulatory) and delayed early genes (replication) and late genes all at once
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How do DNA viruses regulate gene expression
At a transcriptional level
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What do most DNA viruses use to create there proteins?
Host transcription factors and RNA polymerase
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What do DNA viruses use to regulate gene transcription
Transcriptional activators and repressors
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Viral RNAs usually encode ____ proteins
multiple
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Viral promoters contains binding sites for
host or viral encoded transcription factors
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Viruses can interfere in what part of RNA translation
- Post-processing: splicing, methylation, poly-adenelation
- These are all things that viral RNA do not need to do, so this inhibits host protein production but not viral protein production
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Families and important examples of small DNA viruses
- Families: Polyomaviridae, Adenoviridae, Papillomaviridae
- Examples: SV40, polyomavirus, adenovirus, papilloma virus
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Properties of Small DNA viruses
- use host transcription and DNA synthesis machinery
- RNA splicing generates multiple virus proteins
- has capacity to cause tumors
- causes mild disease in humans
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Why do some viruses lead to cancer/tumor
They need to use host machinery so they force the cell into S phase where it is available.
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Why can DNA viruses cause cancer in non-permissive hosts but not permissive hosts
Some non-permissive hosts can allow the S phase stimulators but not the replication and cell death that would stop permissive host cells from causing uncontrolled growth
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SV40, facts:
- Closed circular dsDNA
- Encodes 6 proteins: T-antigens and capsid proteins
- Needs host transcriptional and replication factors
- Early and late phases
- Large T antigen controls host cell cycle
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SV40 regulation of gene expression
See Lecture 4
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Adenoviruses facts:
- Intermediate sized DNA virus, linear dsDNA
- Virion is non-enveloped w/ icosahedral symmetry
- Acute respiratory infections, conjunctivitis, gastroenteritis
- Oncogenic (not in humans)
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Adenovirus gene expression
- Expresses: E1A/B/2/3/4 (Early), IX and IVa2 (delayed early), L1/2/3/4/5 (late)
- All are encoded by splicing and use of overlapping codes
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Early Adenovirus genes do what?
- Viral DNA replication
- turn-on major late promoter
- alter splicing and polyadenylation
- transport viral and cellular RNA
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First gene expressed by Adenovirus
Immediate Early gene (EA1)
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