Life 205 Chpt.13 – Flashcards
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| This is a virus that infects a bacteria |
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| bacteriophage (often shortened to Phage) |
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| Why are viruses difficult to study? |
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| B/c they are obligate intracellular parasites. (They require another living organism as a host) and they are tiny. |
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| A nucleic acid surrounded by a protein coat. |
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| a virion |
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| The protein coat of viruses |
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| a capsid |
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| The nucleic acid together with the protein coat is called a ________. |
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| nucleocapsid |
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| Viruses that do not have an envelope. |
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| naked viruses |
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| How are enveloped viruses different than naked viruses? |
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| In general, enveloped viruses are more susceptible to disinfectants because they damage the envelope and the virus becomes non-infectious. |
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| Most phages are what type of virus? |
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| Naked |
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| What are three ways that viruses can be transmitted from one organism to another? |
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| sexual contact,enteric(oral/fecal) respitory or salivary, vector(arthropods)(e.g. tics)(zootonic) |
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| Viruses so named because they are spread by mosquitos, ticks, and sandflies |
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| arboviruses |
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| These phages exit the host cell by causing it to lyse at the end of an infection cycle. |
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| Lytic (virulent) phages |
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| Viral infections that result in new virus particles |
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| productive infections |
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| What are the five phases of the infection cycle of virulent phages? |
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| 1. attachment 2. genome entry 3. synthesis of proteins and genome 4. Assembly(maturation) 5. Release |
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| These phages have the option of either directing lytic or lysogenic infections |
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| temperate phages |
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| In this type of infection, viral DNA is incorporated into the host cells' genome |
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| lysogenic infection |
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| A change in the phenotype of a lysogen as a consequence of the specific prophage it carries. |
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| Lysogenic conversion |
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| Why is lysogenic conversion inportant from a medical standpoint? |
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| Strains of typical bacteria begin producing toxins that would not be produced by the cell otherwise. This increases the pathogenicity of certain strains of bacteria. |
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| This type of transduction results from a packaging error during phage assembly. Short DNA fragments can be mistakenly packaged into the phage head during assembly. |
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| generalized transduction |
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| A phage head that contains only bacterial genes in place of phage genes cannot direct a phage replication. these are called what? |
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| generalized transducing particles |
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| This type of transduction results from an excision mistake made by a temperate phage during its transition from the lysogenic to the lytic cycle. |
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| What are the 3 main shapes of viruses? |
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| Icosohedral, helical, and complex |
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| What type of virus cause productive infections, but do not kill the host cell? |
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| filamentous |
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| What would be the main cause of a temperate phage remaining in the lysogenic phase? |
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| Low nutrition usually means the virus will stay in the lysogenic cycle |
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| What is the phage both prevents and maintains the lysogenic state? |
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| A repressor protein |
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| How does the repressor protein both prevent and maintain the lysogenic state? |
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| It doesn't allow another phage to enter the cell, but it keeps the one already there in the lysogenic state. |
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| If the DNA of a cell in the lysogenic state is damaged, what happens? |
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| The SOS repair system will activate protease, the protease destroys the repressor, the prophage will be excised (enter the lytic cycle) |
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| What is one way to count phages? |
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| Plaque assay (circular zones of clearing due to cell lysis caused by the phage) |
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| What is one way we could possibly target viruses with antiviral drugs? |
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| Virus replication depends a lot on virally encoded enzymes...they are a good target for antiviral drugs. |
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| What is the 5 step infection process of animal virus replication? |
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| 1. attachment 2. penetration and uncoating 3. synthesis 4. assembly 5. release |
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| What is the main difference between generalized and specialized transduction? |
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| In specialized transduction, only the bacterial genes adjacent to the integrated phage DNA can be transferred. In general transduction, any gene of the donor may be transferred. |
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| In what way do bacteria defend themselves against phages by deterring attachment of the phage? |
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| THey cover the receptor on the cell surface so the virus cannot attach |
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| These protect bact |
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| These protect bacteria from phage infection by quickly degrading incoming foreign DNA by using restriction and modification enzymes. |
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| Restriction-modification system |
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| What is one tool scientists use to remove genes from one DNA molecule and join them to another? |
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| restriction enzymes |
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| How does the bacteria protect its own DNA from degradation by restriction enzymes? |
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| It methylates its own DNA, and only DNA that is unmethylated(phage DNA) will be destroyed. |
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| CRISPR stands for what? |
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| Clusters of Regularly Interspersed Short Palindromic Repeats |
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| A chromosomal region in the bacterial cell that holds spacer DNA |
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| CRIPSR |
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| What is the benefit of CRISPR? |
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| It holds a historical record of phage infections, allowing bacteria and its progeny to block subsequent infections by the same phage. |
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| The concentration of infectious phage particles in the original phage solution |
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| titer |
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| in absorption, the attachment of what triggers endocytosis? |
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| Attachment to receptors |
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| What are the two main methods of viral entry? (absorption) |
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| Endocytosis and membrane fusion |
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| What do viruses usually bind to on the outer cell wall? |
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| specific receptors , glycoproteins on the plasma membrane (often more than one required) |
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| Why can most viruses only infect a certain species? |
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| because they bind to specific receptors not usually found in every living animal |
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| In an _____ virus, the entire virion is taken into the cell. |
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| animal virus |
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| IN this type of penetration and uncoating, the lipid envelope of the virion fuses with the plasma membrane of the host cell and releases the nucleocapsid directly into the cytoplasm. |
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| membrane fusion |
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| In this type of penetration, the virion exploit normal cell receptor-mediated endocytosis to bring themselves into the cell. |
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| endocytosis |
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| Where do most DNA viruses multiply in animal cells? |
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| In the nucleus |
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| IN all viruses, the nucleic acid separeates from its protein coating prior to the start of replication, this is the process of _______. |
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| uncoating |
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| What two distinct, but interrelated events must occur for the synthesis of viral proteins and replication of the genome? |
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| 1.) expression of viral genes to produce structural and catalytic proteins 2.) synthesis of multiple copies of the viral genome. |
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| What type of viruses use the host cells machinery for DNA synthesis? |
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| DNA viruses |
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| What is the main difference btwn dsDNA virses and ssDNA viruses in replication? |
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| The ssDNA must first make a template and then begin making copies. |
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| What type are most RNA viruses? |
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| ssRNA |
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| Where do most ssRNA viruses replicate? |
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| in the cytoplasm |
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| What does RNA replication require? |
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| virally encoded RNA polymerase called replicase |
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| How is the replication of RNA viruses different from DNA viruses? |
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| RNA viruses must synthesize RNA from an RNA template instead of a DNA template. |
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| Why do RNA viruses generally have higher rates of mutations, and why can this be beneficial for them? |
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| The replicase (RNA virsu RNA polymerase) does not have proofreading ability=more mistakes. It can be beneficial because RNA viruses can adapt more quickly than DNA viruses. |
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| A type of antigenic variation that may cause a person whose immune system protected against one viral strain to not work against the next. |
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| antigenic drift |
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| What type of enzyme do reverse-transcribing viruses for? |
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| reverse transcriptase |
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| What does reverse transcriptase do? |
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| synthesizes a DNA strand from an RNA strand. |
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| This kind of virus has a (+) RNA strand and carries reverse transcriptase with it. |
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| retrovirus(HIV) |
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| In what way do most viruses release? |
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| By budding. |
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| The process of a virus acquiring its envelope |
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| budding |
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| Where does assembly take place in an animal virus? |
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| In the nucleus or cytoplasm depending on the virus |
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| How does the virus obtain its viral envelope through budding? |
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| The virus protein spikes insert themselves into specific regions of the host cells membrane. Matrix proteins accumulate on the inside surface of those regions. Assembled nucleocapsids then extrude from the cell becoming covered by a layer of matrix protein and lipid envelope in the process. |
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| Does budding cause cell death? |
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| not necessarily. The membranes can be repaired after the viral particles exit. |
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| How are naked viruses released? |
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| Many viruses trigger apoptosis prior to the release of viral particles. |
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| How do enveloped viruses exit the cell? |
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| budding |
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| Why are virally encoded enzymes medically important? |
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| Because they are important in many viral processes and can be targeted to stop the virus from infecting. |
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| What type of infection is characterized by a sudden onset of symptoms and a relatively short duration? |
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| Acute infections |
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| This type of infection can continue for years or even life |
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| persistent infection |
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| The silent viral genome |
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| provirus |
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| genes that stimulate cell growth |
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| proto-oncogenes |
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| Genes with similar DNA to proto-oncogenes that interfere with the cell's own control mechanisms. |
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| oncogenes |
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| What are most tumors caused by? |
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| Mutations in the host genes that regulate cell growth |
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| WHat is an example of a virus that is associated with the development of cancers? |
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| HPV, EBV(epstein barr virus), HHV-8 (they appear to interfere with the function of an important tumor supressor gene) |
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| What are the most common viral causes of cancer? |
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| DNA tumor viruses |
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| How can a vaccine prevent cervical cancer? |
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| The vaccine would hopefully cause the individual to build up immunity to the virus HPV, so that it could not cause cancer |
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| What are some ways to study animal viruses? |
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| 1. innoculate live animals with the virus 2. cell culture (tissue culture) |
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| In this type of culture, animal cells are grown in a liquid medium contained in a special screw-capped flask |
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| cell culture (also know as a tissue culture) |
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| tissue removed from an animal then processed to get individual cells |
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| primary culture |
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| Distinct morphological alterations in infected cells.(cells may change shape, detach from surface, or lyse) |
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| cytopathic effect |
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| a distinct region where the site of viral replication is |
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| an inclusion body |
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| What is one of the most precise methods for determining the concentration of animal viruses in a sample? |
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| A plaque assay |
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| How are plaque assays different from animal virus to bacteriophage? |
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| A monolayer of tissue culture cells is the host instead of the broth with bacterial cells in it. |
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| How can the viral titer be estimated? |
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| using a quantal assay |
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| in this method, several dilutions of the virus preparation are administered to a number of animals, cells, or chick embryos |
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| quantal assay |
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| What is the titer of the virus? |
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| the dilution at which 50% of the inoculated hosts are infected or killed. |
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| How do we measure the titer of the virus? |
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| ID50: Infective dose LD50: Lethal dose |
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| WHen red blood cells agglutinate (clump) |
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| hemagglutination |
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| When does hemagglutination occur? |
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| When individual viral particles attach to the surface molecules of multiple red blood cells simultaneously. |
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| What does hemagglutination show? |
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| That there is a high concentration of viral particles in the blood |
