Term
| 5 things that a virus IS: |
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Definition
1. Small, infectious, obligate intracellular parasite.
2. A particle containing a DNA or an RNA genome.
3. An agent that directs synthesis of viral components using cellular machinery
4. Assembled de novo with newly synthesized components within a host cell.
5. An agent that creates progeny particles that propagate the viral genome to the next host cell. |
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Term
| 6 things that a virus IS NOT: |
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Definition
1. A cell
2. A simple autonomous organism
3. A protein-only infectious agent (as in prions).
4. A nucleic acid only infectious particle (viroid).
5. A transposable element
6. Alive |
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Term
| What are Koch's postulates (4 points)? |
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Definition
1. The organism must be found in the lesion.
2. The organism must be isolated in pure culture.
3. The inoculation of a pure culture of the organism into a host must cause the disease.
4. The organism must be recovered from the inoculated host. |
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Term
| Why do viruses fail Koch's postulates? |
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Definition
| Viruses cannot be isolated in pure culture (They require a host cell). |
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Term
| What are the 6 VIRAL factors that govern viral spread? |
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Definition
1. Viral stability and transmission route.
2. Degree and duration of infectivity (higher production of viruses increases transmission, persistent infections lengthen the transmission period)
3. Pathology (less pathogenic viruses that cause persistent infections spread better, because they are not killing their hosts or making them stay inside because they are sick).
4. Immune escape/Antigenic variation.
5. Immune evasion. Active subversion of the immune system by a virus (there is some viral factor that actively inhibits some aspect of the immune response).
6. Animal Reservoirs. Obviously, if there is an animal reservoir, viral spread is going to increase, as the number of potential hosts has increased. |
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Term
| What HOST 6 host factors govern viral spread (3 general host factors, 3 human specific host factors)? |
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Definition
All hosts:
1. Higher population density increases spread (more permissive hosts).
2. Social factors (reproduction cycle, dietary habits/nutrition, cyclical mobility)
3. Herd immunity
Social Factors
4. Social Taboos/Technological prowess (vaccines, antivirals, etc.)
5. Public health (surveillance, sanitation, education, vaccination).
6. Medical care |
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Term
| Why can viral components be detected before antibodies? |
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Definition
| Viral titer generally becomes detectable way before antibodies, because it takes time to mount an adaptive response. |
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Term
| What techniques are used to detect viruses? 5 main techniques |
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Definition
1. ELISA detects viral proteins.
2. PCR and RT/PCR to detect and quantify viral titer (as in qPCR).
3. Hemeagglutination
4. Electron microscopy
5. Viral Culture |
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Term
| What is hemeagglutination? |
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Definition
| A sample with virus is serially diluted. Then RBCs are added to each dilution. This only works for viruses which bind to RBCs. An example is the Influenza virus. Influenza express a glycoprotein called hemeaglutinin glycoprotein. This protein binds to sialic acid receptors on Influenza virus, and this causes RBCs to aggregate as more than 1 RBC is binding to the same virion. |
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Term
| What can you look for in a host to determine response to virus (2 things)? |
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Definition
1. Antibodies
2. Pathological products |
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Term
| What are the important differences between functional assays and physical assays? |
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Definition
1. Functional assays (like a plaque assay) ONLY DETECTS THE NUMBER OF VIRAL PARTICLES CAPABLE OF REPLICATING IN THE DEFINED CONDITIONS OF THE ASSAY.
2. Physical assays measure the number of viral particles or genomes, including replication incompetent particles/genomes (examples include qPCR/qRT-PCR, S/N/W blots, ELISA, EM). |
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Term
| What is a viral matrix, and what function does it serve in HSV? |
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Definition
1. A viral matrix is a layer of proteins just under the envelope which links the envelope with the capsid.
2. HSV matrix is specialized and is called the tegument. These proteins provide structural support and serve regulatory functions when released into the host upon entry. |
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Term
| Give some examples of the wide variety of genome structures/arrangements in the world of viruses. |
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Definition
1. RNA/DNA
2. ds/ss
3. Linear/Circular
4. +/- or both polarities
5. Complete or incomplete
Some viruses harbor multiple genomic isomers/polarities
6. A population of viruses may contain many non-infectious (defective) genomes, and some genomes carry insufficient genomes, which require a cell to be coinfected by a complimenting genome.
7. A virus may require coinfection with a different virus to replicate (HDV requires HBV coinfection).
8. Segmented genomes (especially prevalent in RNA viruses like Influenza and rotavirus). Often, a given viral particle will contain >/< the required number of segments to replicate, and requires coinfection with a virion containing the missing segments.
9. Most viral genomes are haploid, with the exception of retroviruses, which possess 2 genomes per particle. |
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Term
| Why do viruses evolve faster than whole organisms (4 reasons)? |
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Definition
1. Short rep cycles.
2. Lots of progeny in each cycle.
3. Replication is error prone (especially when virally encoded polymerases are involved, as they lack a proofreading mechanism.
4. Viruses can recombine genetic material with other viruses or with the host. |
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Term
| Describe the relationship between + polarity DNA, - polarity DNA, mRNA, and protein. |
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Definition
1. + DNA is identical to mRNA
2. - DNA is complementary to + DNA and mRNA, and is the template for mRNA transcription.
3. Only + mRNA is tranlated. |
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Term
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Definition
| The number of asymmetrical units per capsid face. |
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Term
| What are the 2 models for initial evolution of viruses? |
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Definition
1. Degeneration: A parasitic cellular organism (like a bacteria) lost the selective pressure to make all of its own molecular machinery, maintaining in its genome only those factors essential for replication and spread.
2. Mobile genetic elements developed ability to spread. |
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Term
| Stages of a viral infection (6 stages): |
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Definition
1. Entry (membrane fusion or endocytosis).
2. Uncoating of genetic material inside cell.
3. Gene expression
4. Replication
5. Assembly
6. Exit (either budding or lysis) |
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Term
| Describe the replication cycle of Yellow Fever Virus. |
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Definition
1. Yellow Fever Virus is an enveloped, positive polarity, unsegemented RNA virus.
2. Mosquito transmission (replication competent in both hosts).
3. Genome is directly translated (because + polarity) to form a polyprotein, which is then cleaved to make mature proteins.
4. Non-lytic
5. Cytoplasmic replication with RDRP. |
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Term
| Name one of the biggest factors determining a virus's tropism. |
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Definition
| Presence of attachment receptor (HBV tropism partly due to NTCP (Sodium Taurochlorate |
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Term
| What do co-receptors do (4 things)? |
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Definition
1. Stabilize primary binding.
2. Promote a conformational alteration required for entry
3. Part of a membrane fusion complex
4. Induce endocytosis. |
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Term
| What are 2 ways that viruses get in cells? |
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Definition
1. Membrane fusion (requires fusion peptides on virion surface
2. Endocytosis |
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Term
| What are some factors governing uncoating of a viral genome (breakdown of viral capsid)? |
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Definition
| Proteolysis, phosphorylation, pH change... |
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Term
| How does influenza virus enter a cell? |
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Definition
1. Binding: HA binds receptor proteins with sialic acid glycosylations.
2. Endocytosis
3. Membrane/Envelope fusion: Acidification and rearrangement of "spring loaded" HA subunits. This exposes fusion peptides.
4. Uncoating: Acidification of viral particle interior causes dissociation of matrix particles the genomic RNPs.
5. Nuclear import (active transport of RNP to nucleus) |
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Term
| What are 2 mechanisms of entry by naked viruses? |
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Definition
1. Membrane disruption
2. Genome transfer (genome injection across PM or endocytic vesicle membrane). |
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