Microbio 310: Exam 2
73 Cards in this Set
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What is a virus?
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It is a genetic element which requires a host to replicate
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What is a virus particle? What is its form and function?
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It is the extracellular form of a virus
-Facilitates transmission
-Contains nuclic acid genome & protein coat
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Describe the genomes of viruses?
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-Can be either RNA or DNA
-Some are circular but most are linear
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How are viruses classified?
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By the hosts that they infect
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What is the size of viral DNA relative to other cells?
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It is generally much smaller
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Virus structure: Capsid
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-The protein structure that surrounds the genome of a virus
-Precise, repetitive pattern.
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Virus structure: Capsomere?
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Smallest subunit of the capsid visible through an electron microscope
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Virus Structure: nucleocapsid?
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Complete complex of nucleic acid and protein packaged in the virion
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Virus Structure: Enveloped virus?
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Virus that contains additional layers around the nucleocapsid
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Describe helical symmetry of viruses?
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Rod shaped
-length determined by length of nucleic acid
-width determined by size and packing of proteins
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Describe icosahedtal symmetry of vituses?
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Spherical viruses (like HPV)
-Most efficient
- Think jimmy neutron viruses in the stomach
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What is significant about enveloped viruses?
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Their membrane makes initial contact with the host cell.
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What is the significance of a complex virus?
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-It is a viron composed of several parts (spherical &icosahedral tails)
-Bacterial viruses are typically complicated like this
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Viral Enzymes Function: Lyzozyme?
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-Makes hole in the cell wall
-lyses bacterial cell
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Viral Enzymes Function: Nucleic acid polymerases?
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Catalyze the formation of DNA essential for Viral replication
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Viral Enzymes Function: Neuraminidases?
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-Enzymes that cleave clycosidic bonds
-Allows liberation of viruses from the cell
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What are characteristics of viral growth?
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-viruses replicate only in certain types of cells or organisms
-bacterial viruses are the easiest to grow
-animal viruses (and some plant) can be cultivated in cultures
-Plant viruses are the most difficult because they normally require the whole organism
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What is a titer?
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Number of infectious units per volume of fluid
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What is a plaque assay?
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It's like a bacterial colony.
One way to measure infectivity
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What is a plaque?
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The clear zones that develop on lawns of host cells
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Efficiency of plating?
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The number of plaque forming units is almost always lower than than direct counts
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What is the intact animal methods?
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Some viruses do not show changes in cell cultures, yet cause death or disease in animals
-virus is diluted
-animal is infected
end point is calculated
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What are the phases of virus replication?
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1) Attachment
2) Entry
3) synthesis
4) assembly
5) Release
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Stages of viral replication: attachment?
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the virus attaches to a host cell
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Stages of viral replication: entry?
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The viron penetrates the host cell
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Stages of viral replication: synthesis?
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The virus directs the host to produce the viral nucleic acid using the host's own metabolism
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Stages of viral replication: Assembly?
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The viral capsids are packages into new virons
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Stages of viral replication: release?
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The mature virons are release from the host cell
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What are the parts of the latent period for viral growth?
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Linear: eclipse of host+maturation
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What is a permissive cell?
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A host cell that allows for the complete replication of a virus to occur.
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Characteristics of viral attachment?
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-Highly specific
- requires complementary receptors on both virus and host
-bonding causes changes on both ends that allows for penetration
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What is one method of eukaryotic immune defense?
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The interference of RNA
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Immune Defense: CRISPR?
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-Takes place in prokaryotes
-Similar to RNA interference
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Immune Defense: Restriction Modification System?
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-Double Stranded DNA-destruction system
-cleaves DNA at certain points
-Host DNA is immune due to modifications at recognition sites
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What are two mechanisms by which a virus tries to evade bacterial restriction systems?
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- Chemical modification of viral DNA
-Production of proteins that inhibit host cell restriction systems
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What was discovered by David Baltimore, Howard Temin, and Renato Dulbeccco?
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Discovery of retroviruses and reverse transcriptase
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What does the Baltimore classification system describe?
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Viruses based on relationship of viral genome to its mRNA
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Class I Virus?
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Double Stranded DNA
dsDNA
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Class II Virus?
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Single stranded DNA virus
ssDNA
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Class III Virus?
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dsRNA
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Class IV & V Viruses?
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ssRNA (+ or -)
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Class VI virus?
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Retrovirus
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Class VII Virus?
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dsDNA Viruses that replicate through a mRNA intermediate
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What is the pattern of viral nucleic acid production?
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Viral genome serves as template for viral mRNA
-In some cases transcriptional enzymes are contained in the viron
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+ strand RNA virus?
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Single-stranded RNA genome with same orientation as its' mRNA
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- strand RNA Virus?
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single stranded mRNA virus with complementary genome
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Retroviruses?
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Animal viruses that are responsible for causing cancers and IDS.
-Class VI & VII
-require reverse transriptase
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Viral Proteins: Early Proteins?
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-synthesized soon after infection
-necessary for replication
-synthesized in smaller amounts
-typically function catalytically
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Viral Proteins: Late Proteins?
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Synthesized later
-make-up viral coat
-structural components
-made in larger amoutns
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What is reverse transcriptase?
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It is used to reverse transcribe viral DNA from mRNA. This DNA is then integrated, and reproduced along with the DNA of the host
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Structure of Bacterial viruses?
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-aka Bacteriophages
-Very diverse
-Most contain dsDNA
-Most are naked; some enveloped
-Structurally complex, heads tails, other components
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Viral Life Cycle
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-Virulent: Viruses lyse host cells after infection
-Temperate: Viruses replicate their genomes in tandem with host genome without killing the host
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What is lysogeny?
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State where most virus genes are not expressed and virus genome (prophage) is not replicated with host chromosome
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What is a Lysogen?
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A bacterium containing a prophage
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What is a mutation?
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a Heritable change in DNA sequence that can lead to a change in phenotype
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What is a mutant?
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A strain of a cell or virus differing from the parental strain
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What is the wild-type strain?
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Typically refers to a strain isolated from nature
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What is a selectable mutation?
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The mutations that give the mutant an advantage
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What is a nonselectable mutation
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Neither have an advantage or disadvantage
-requires screening
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What is an induced mutation?
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A mutation made enviornmentally or deliberately.
-ex. exposure to radiation or o2 radicals
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What is a spontaneous mutation?
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A mutation that occurs without external intervention
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What is a point mutation?
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A mutation that changes only one base pair
-Can change single amino acid, leave incomplete protein, or no change at all
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What is a silent mutation?
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Does not affect the amino acid sequence
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What is a missense mutation?
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Amino acid changed; polypeptide altered
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What is a nonsense mutation?
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Codon becomes stop codon, polypeptide is incomplete
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What is a frameshift mutation?
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Deletion or insertion that results in the shift of the reading frame
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What is a Reversion?
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Alteration of DNA that reverses the effects of a prior mutation
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What is a revertant?
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Strain in which the original phenotype is restored
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What is a same-site revertant?
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The mutation site is at the same site as the original mutation
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What is a second site revertant?
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A mutation that is at a different site on the DNA. Supressor mutation compensates. Think cover-up make-up.
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What is a mutagen?
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Chemical, physical, or biological mechanisms that increase the mutation rates
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What are acridines?
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Chemical mutagens that cause frameshift mutations
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What are examples of non-ionizing radiation?
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UV radiation
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Microbio 310: Exam 1