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49 Cards in this Set
- Front
- Back
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how were viruses discovered? |
Ivanoski: passed an extract of diseased plant through filter that couldn’t pass bacteria, but passed agent. therefore, much smaller than anything they had seen before |
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general flow of the major discoveries |
-demonstrated that viruses can cause disease in humans. -isolated and purified a virus for the first time to determine what they were made of. -used a newly developed electron microscope to visualize viruses for the first time. |
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General size of virus? What is meant by obligate intracellular parasites? Infect? Structure? |
-very, very small (~0.3 micrometers) -no growth/reproduction, metabolic systems, not alive -can infect all forms of life -protein shell that contains genome |
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varieties in viral genomes |
-can utilize DNA vs RNA (not both) -single stranded, double stranded, partially double stranded -linear or circular |
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+ sense vs - sense RNA genomes |
+: looks like mRNA, genome is mRNA; can be translated directly into protein by ribosomes -: genome needs to be converted into + before being translated |
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RNA genomes: special ability to replicate? |
Both + and - sense RNA genomes need an RNA dependent enzyme to create more RNA: ~~~~> RNA polymerase |
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what is a capsid? what does it do and what are its levels of organization? |
capsid: outer protein shell that protects the genome and in some cases helps the virus attach to cells protomer: individual proteins that make up capsid capsomer: protomers assembled into higher order structures capsid: capsomers assembled to form an intact structure nucleocapsid: capsid + genome |
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three major shapes of capsids |
helical:capsid proteins form a hollow cylinder with the genome inside polyhedral:protomers assemble into flat triangles and assemble into capsids with many sides. Each point of connection is called a vertex. The capsid is made first with the genome added later. complex: either have a complicated structure or their shape is not regular. |
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what is the viral envelope? where does it come from? function? what does it contain? obtained? |
Viral envelope: phospholipid membrane that surrounds the nucleocapsid -acquired from host membrane when the virus buds, usually through the plasma membrane -provides extra layer of protection to the nucleocapsid -contains viral glycoproteins used for attachment to host cells |
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what is the viral matrix? function? |
viral matrix: a layer of protein between nucleocapsid and envelope function: budding, entry into new host cells, pathogenesis |
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three major criteria for classifying viruses |
-genomic structure -capside structure -envelope structure |
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three outcomes of standard viral infection |
Lysis/lytic infection: host cell is killed, new viruses are released. Virus replicates: no cell death/permanent changes Virus integrates: genome integrates into the host cell genome or permanently establishes itself |
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what two things must a virus do upon entering a host cell and what is its goal in doing so?
why should we care? |
virus must invade host cell and take over its machinery in order to create more of itself. replication leads to cell death and disease. treatments must be virus specific with understood replication = hard. |
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What occurs during attachment? what proteins are involved (on the virus and host)? |
Adhesion proteins on the surface of the virion bind to specific receptors on the surface of susceptible cells. |
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attachment different for enveloped vs naked viruses? |
Envelope: adhesins are embedded in the membrane envelope Naked: adhesins are associated with the capsid or directly the capsid itself |
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What limits the viral host range and how many different types of cells it can infect within a host? |
viral host range limited by how many cellular receptors it is able to attach to. Some use a single cellular receptor on a single cell type in a single species = limited. Others use common receptors found on many cell types and species = interspecies. |
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how is attachment stopped? |
If attachment is prevented, than no infection can occur, which is what antibodies do. Diseases like HIV are naturally mutated and their receptors can provide resistance though. |
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What mechanism do bacteriophages use to enter/penetrate? |
They secrete phage lysozyme to degrade bacterial cell wall. The phage tail drives through the wall and plasma membrane and injects its DNA into the cytosol of target cell. |
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What do naked viruses use to enter/penetrate? |
Nucleocapsid is phagocytosed by host cell and brought into a membrane vesicle |
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What are the different ways that enveloped viruses get it (e.g. at which cellular locations can the envelope fuse with the host membrane)? |
Some envelopes able to directly fuse with PM and release their nucleocapsid into the cytosol. Others, entire virus w/ envelope included is phagocytosed into a vesicle, and envelope fuses with vesicle membrane, causing nucleocapsid to be released. |
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Where do DNA viruses have to go when compared to RNA viruses? How do they get there? |
RNA viruses are able to replicate in the cytosol and don’t have to move or target anything specific. DNA viruses are able to replicate their genome in the host nucleus, and the nucleocapsid has to use microtubules, intermediate filaments or microfilaments to get there. |
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What is meant by uncoating? |
The genome needs to be moved away from the capsid to allow for replication of the genome and transcription to be undergone. |
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different mechanisms of uncoating if the virus in a bacteriophage or eukaryotic cell virus. |
Phage: occurs during entry when the capsid injects the genome into the cell Eukarycell virus: if nucleocapsid is in vesicle, enzymes w/in that vesicle/lyso will degrade the capsid, which releases the genome and allows it to be released into cytosol. If nucleocapsid is already in cytosol, the genome is able to be uncoated via two different mechanisms: ~cytosolic enzymes degrade capsid |
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Why is viral genome replication necessary? |
goal of replication is to make more virus, because it needs new copies of the viral genome & new virion structural proteins to continue to infect the host |
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Where and how do DNA viruses replicate their genome (what do they use)? |
Viral DNA in the nucleus is replicated and transcribed by host polymerase enzymes. |
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different DNA viruses |
Hepadnavirus: includes hepatitis B Herpesvirus: includes chickenpox Papovirus: includes HPV Poxvirus: includes smallpox |
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Where and how do RNA viruses replicate their genome? What limitations do they have and what enzyme do they have to provide as a result? |
Genome replication takes place entirely in the cytosol. Since host cells cannot copy RNA into RNA, viruses must bring in their own RNA dependent RNA polymerase enzyme. |
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mechanistic differences between + and – sense RNA viruses in terms of how they have to copy their genome |
+ sense: an immediate infection that resembles mRNA - sense: slower, but still effective - the virus is uncoated, the genome is released, and the ribosome doesn’t recognize it; must bring RNA dependent RNA polymerase enzyme into host to use during transcription process. |
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different RNA viruses |
Filovirus: includes Ebola Picornavirus: includes polio Paramyxovirus: includes influenza and measles Rhabdovirus: includes rabies |
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How are retroviruses and lysogenic phages similar in terms of how they replicate their genome? |
They both replicate their genome by integrating it into the host genome and then waiting for the host to go through cell division. |
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How do retroviruses turn their RNA genome into double-stranded DNA? What do they do with that new DNA genome? |
Genome in virion is RNA. It is converted into DNA using reverse transcriptase, which integrates the new DNA genome into host chromosomes with integrase. The genome is then stable and can be replicated by the host. |
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lysogenic-lytic cycle for bacteriophages |
Lysogenic cycle: the viral genome integrates into host bacterial genome. The bacteria copies it during binary fission. No new viral particles are made during lysogeny. Lytic cycle: can be reentered by cutting viral genome back out and making new viral particles |
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What occurs during assembly and where does it occur? |
New capsids have to assemble and new genome have to be packaged into said capsids. Some also need to acquire a matrix or envelope. The location of assembly varies for each virus family. Some occur in the nucleus, cytosol, or specific membranes. |
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How do lytic phages and naked animal viruses escape from the cell? |
Many secrete enzymes that actively kill the host cell, and the virus is released when the cells pop open. Others make the cell so unhealthy that they passively die and release the virus. |
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What is meant by cytopathic effect? |
The unhealthy state of infected cells that can be observed microscopically. |
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What about enveloped viruses? What is meant by budding? What is meant by egress? |
Enveloped viruses need to push their way through the host membrane to make an envelope; often made of the plasma membrane but can be internal membranes as well. This process is called budding. If it buds at the internal membrane, it needs to follow secretory pathway out of the cell, called an egress. |
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What is the difference between a persistent and latent infection? |
persistent: still infectious because virus produced in low levels over long period of time with few symptoms
latent: not infectious but viral genomes left behind can become reactivated in a lifetime |
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What are the two major ways that viruses can cause cancer? |
A virus can cause cancer by integrating the viral genome into the host genome in a bad spot, causing a disruption of normal cell cycle/cell death genes, or by encoding an oncogene. |
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What is an oncogene? |
Genes that help turn on cell division (or turn off cell death) abnormally. |
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viruses that cause cancer |
Epstein-Barr virus: causes Burkitt’s lymphoma Hepatitis B/C virus: causes liver cancer HTLV: retrovirus that causes leukemia Human papilloma virus: the leading cause of cervical cancer, encodes several oncogenes |
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What is an oncolytic virus and what gives it that ability? |
Some viruses have a unique ability to target and kill cancer cells better than normal cells, called oncolytic viruses. Their oncolytic ability is due to mutations in cancer cells that suppress their natural anti-viral infection response. |
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How do we cultivate lytic bacteriophages (what is a plaque)? |
We mix a bacteria and a virus within molten agar and pour it on top of another solidified agar plate. The bacteria will grow into a single thin layer on the surface, making it look hazy. The phage will infect single cells and kill them, and spread to/kill cells nearby. The clear area formed is a plaque. |
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How do we cultivate animal viruses that are hard to grow in the lab? |
Some are cultivated inside live animals (mice, rabbits, guinea pigs) and some grow well in embryonated chicken eggs. Viruses are most commonly cultivated in isolated animal cells (human or not) grown in Petri dishes. |
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What is tissue culture and what is the difference between primary vs continuous cell lines? |
Growing cells outside the animal is called cell culture or tissue culture. Primary cell lines are isolated directly from an animal but only last a few generations. Continuous cell lines are tumor cells that divide indefinitely. |
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six different ways in which we quantitate viruses |
Direct quantification via EM Hemagglutination Immunological techniques Molecular bio techniques Plaque assays Quantal assays |
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What are prions, how were they discovered, and how do they cause harm to animals? |
Prions: infectious, misfolded proteins. Took brains from infected individuals, ground them up, and purified the fraction that was most infectious. only proteins found, and accumulated brain to form plaques. Cause harm to animals because once a prion is introduced, it causes other proteins around it to also misfold, causing assay clumps and killing off neurons. |
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How do prions work mechanistically? |
The normal form of protein (called PrPC) functions to regulate cell death. Prions (PrPSC) work by binding to PrPC and causing them to misfold, and lots of PrPSC are produced to form plaques. |
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What are some diseases caused by prions? |
Humans: kuru, CJD, FFI Cows: mad cow disease Sheep: scrapie |
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What are viroids and how do they cause disease to plants? |
Viroids are small, single stranded RNAs that are infectious to only plants. They cause disease by binding to cellular RNAs and causing their subsequent destruction. It spreads through pollen and infect plants via open wounds. |
