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75 Cards in this Set
- Front
- Back
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Study of viruses |
Virology |
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3 domains of life |
Bacteria Archaea Eukarya |
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To which domain of life do viruses belong? |
None They are not alive |
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Requirements for Life |
1. Made of cells 2. Grow and maintain structure by metabolizing chemicals from the environment • Have ATP-generating metabolism • Have ribosomes for protein synthesis 3. Respond to external stimuli 4. Reproduce and pass on their genes to their offspring • Posses both DNA and RNA 5. Evolve and adapt to their environment |
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What separates viruses from life? |
1. Acellular 2. Obligate intracellular parasites 3. No ATP generating system 4. No ribosomes or protein synthesis 5. Have DNA or RNA, not both |
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Host range |
Refers to the spectrum of host cells a virus can infect |
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What determines a virus's host range? |
The virus's ability to interact with receptor molecules on the host cell surface which allow the virus entry into the cell* * in the case of bacteriophages, the receptor molecules allow the virus to inject its DNA into the cell |
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Why are some people immune to HIV? |
Past pandemic (black death) favored a mutation which removed a receptor required by the HIV virus to gain entry to WBC |
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How specific is the host range of a virus? |
Most viruses infect one specific type of cell in one species However, some have been shown to break their host range barrier and infect other species |
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What is an example of a virus that can break their host range barrier? |
Influenza can infect many types of animals by recombining with other types of flu viruses |
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What animal can act as a melting pot between the avian flu virus and the human flu virus? |
Piggy pigs |
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Viral size |
20nm - 100nm+ |
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Virion |
A complete, fully developed, infectious viral particle |
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Parts of a typical virus |
Nucleic acid Capsid |
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Nucleic acid |
The core of the virus DNA or RNA, never both |
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Capsid |
Protein coat that surrounds the nucleic acid Made of individual protein units called capsomeres |
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Additional viral structures |
Envelope-lipid membrane Enzymes |
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Envelope-lipid membrane |
Comes from an infected cell On the outside of the capsid Sometimes have the addition of spikes |
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Spikes |
Protein-carbohydrate complexes on viral envelopes that may aid in attachment |
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Viral Enzymes |
Aid in viral replication May be carried inside the virus |
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Types of viral nucleic acid |
ssDNA dsDNA ssRNA dsRNA |
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ssRNA |
Positive strand (can act as mRNA) Negative strand |
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Viral Genome |
Can be linear, circular, or in segments |
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Viral morphology |
1. Helical 2. Polyhedral 3. Enveloped 4. Complex Structure |
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Helical |
A rod made of helical capsomeres |
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Polyhedral |
Icosahedral (20 equal sides) Spherical Many sided |
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Enveloped |
Envelope can surround the helical or spherical capsid |
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Complex structure |
Everything else that won't fit under the other categories |
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Examples of complex structures |
Bacteriophages Poxviruses |
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Bacteriophages |
Viruses that infest bacteria Shaped like molecular syringes |
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Poxviruses |
Don't have clearly defined capsids |
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Taxonomy of viruses |
Determined by the International Committee on Taxonomy of Viruses Based on how they store nucleic acid and how they make their mRNA |
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How many recognized orders of viruses exist? |
7 |
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How many viral species have been classified? |
The minority (3,187) |
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Challenges of growing viral cultures |
All viruses are obligate intracellular parasites |
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Growing bacteriophages |
Easiest to grow (by using a lawn of bacteria on a spread plate) Infection will result in plaques |
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Plaques |
Clear zones where bacteria have been killed by bacteriophages |
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Methods of growing animal viruses |
Living animals Chicken embryos Cell cultures |
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Living animals |
Expensive and time consuming |
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Chicken embryos |
Used to be the most common method Still used to produce many vaccines |
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Cell cultures |
Most common method for growing viruses today Easier to maintain than living animals |
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Types of viral cell cultures |
1. Primary cell line 2. Diploid cell line |
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Primary cell lines |
Derived from tissue slices Die out after a few generations |
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Diploid cell lines |
Developed from human embryos Greater reproductive potential Maintained for up to 100 generations |
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Continuous cell lines |
- Cancerous cells - Almost immortal under right conditions - May be maintained indefinitely |
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Commonly used continuous cell line |
HeLa cells Cervical cancer from Henrietta Lacks in 1951 |
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Cycles of bacteriophage replication |
Lytic cycle Lysogenic cycle |
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Lytic cycle |
Bacteriophages reproduce and quickly kill the bacterial cell |
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Steps of the lytic cycle |
1. Attachment 2. Penetration 3. Biosynthesis 4. Assembly (maturation) 5. Release by lysis |
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Attachment |
Binding sites must match receptor sites |
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Penetration |
Viral DNA is injected into bacterial cell |
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Biosynthesis |
Genome replication, transcription, translation |
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Maturation |
Virus particles are assembled |
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Release by cell lysis |
Cell is killed and cell contents released |
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Lysogenic cycle |
Phage DNA hides out in the bacterial chromosome until its ready to reproduce itself |
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Prophage |
The viral genome hidden in the bacterial chromosome |
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Phage conversion |
Occurs when the infecting phage changes something in the host bacteria's life cycle |
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Burst size at the end of the lytic cycle |
50-200 new viruses |
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Bursting time in release by lysis |
20-40 minutes |
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Entry |
But receptor mediated endocytosis or fusion of viral envelope with cell membrane |
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Uncoating |
Separation of the capsid from the viral genome |
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What are some examples of phage conversion? |
Corynebacterium diphtheriae • only pathogenic when infected by a virus (prophage carries the gene coding for the toxin) Clostridium botulinum • toxin only produced when undergoing lysogenic conversion Escherichia coli • Shiga toxin produced by the pathogenic strains is encoded by a prophage gene |
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What sets enveloped viral replication apart from non- enveloped? |
- penetration by fusion (viral envelope and cell membrane fuse together) - Release by budding |
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Budding |
- Virus pinches out through the host cell membrane - Viral proteins already incorporated in the membrane, which becomes the envelope |
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Non-enveloped animal virus replication |
1. Attachment 2. Entry 3. Uncoating 4. Biosynthesis 5. Maturation/Assembly 6. Release by Lysis |
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Types of viral RNA |
+ strands - can be directly translated into proteins - strands - have to be first transcribed into + strands before they can be translated |
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Retroviruses |
Discovered in 1975 Instead of following central dogma of molecular genetics, they follow this formula: RNA => (reverse transcriptase) => DNA => mRNA => Protein |
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Retrovirus Replication |
1. Virus enters via fusion with cell membrane 2. Virus uncoats, releasing viral RNA and viral enzymes 3. Viral RNA is converted to viral DNA by the enzyme reverse transcriptase 4. Viral DNA is integrated into host cell DNA (provirus) 5. Provirus is transcribed and new retroviruses are made and released |
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Provirus |
A retrovirus whose DNA has been integrated into the host cell DNA Can "hide out" for years at this stage |
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Viroids |
Naked pieces of RNA with no capsid |
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Size/morphology of viroids |
300-400 nucleotides long Closed, folded |
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What types of disease do viroids cause? |
Only plant pathogens that we know of Ex. Potato spindle virus |
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Prions |
Proteinaceous infectious particles Cause vacuoles (spaces) to form in the brain |
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Diseases caused by prions |
Scrapie Bovine Spongiform Encelopathy CJD Kuru |
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Viral Goals |
1. Get in host cell 2. Take over and reproduce 3. Get out of cell 4. Infect more cells |
