Micro Final

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Virus

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genetic element that cannot replicate independently of the living host cell but that possesses an extracellular form

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Virion

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extracellular form (virus particle)

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Capsid

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protein shell surrounding the nucleic acid

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Capsomeres

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assemblies of a protein or proteins into the smallest morphological unit seen with the electron microscope

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Nucleocapsid

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complex of nucleic acid & protein packaged in the virion

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Naked viruses

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no envelope

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Enveloped viruses

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have lipid bilayer around nucleocapsid

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Bacteriophage

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virus that infects bacteria

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Rod-shaped virus

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have helical symmetry

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Spherical viruses

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have isosahedral symmetry

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Isosahedron

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symmetric structure containing 20 triangular faces & 12 vertices that is roughly spherical

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Permissive hosts

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cells that support complete replication cycle of a virus

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Virus infectious unit

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smallest unit that causes detectable effect when added to susceptible host

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Titer

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number of infectious units per vlume of fluid

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Plaque

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clear zone of lysis resulting when a virion initiates an infection on a layer of host cells

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Plaque assay

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counting areas of clearing on a host lawn of cells

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Plaque forming units

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result from infection by single virus particle or infectious unit

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Endocytosis

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penetration in which the entire virus enters the host cell

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Uncoating

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process in which the virion loses its outer coat & the viral genome is exposed

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Circular permutation

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individuals within a population that have the same genes but in different orders

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Concatemer

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occurs in T4 when genome is replicated as a unit & several units are combined and later cut into specific lengths to fit into a phage head

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CRISPR

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mechanism by which bacteria eliminate invading viruses

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Temperate viruses

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dsDNA viruses that infect & establish long-term stable relationship with host

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Lysogeny

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state in which most viral genes are not transcribed and the viral genome is replicated in synchrony with the host chromosome & passed to daughter cells

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Lysogen

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a cell harboring a temperate virus

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Prophage

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viral DNA that replicates along with host cell while viral genes for virulence are repressed

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Rolling cycle replication

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one strand is nicked & rolled out to use as template for synthesis of the complementary strand

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Transduction

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transfer of genetic material from one host to the next

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Integrase

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phage-encoded enzyme that recognizes genome attachment sites & facilitates integration of the lambda genome

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Lambda repressor (cI protein)

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represses transcription of other lambda-encoded genes & allows integration of lambda gene into host’s chromosome, leading to lysogeny

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Cro

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viral gene which sends virus down lytic pathway (represses activator protein of cI)

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RNA replicase

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enzyme that replicates viral RNA genomes

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Overlapping genes

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allow virus to produce more than 1 polypeptide from a single gene

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Latent infection

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delay between infection & host lysis

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Transformation

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conversion of normal cells into tumor cells

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Retrovirus

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animal virus that contains a + ssRNA genome that is replicated via a DNA intermediate (uses reverse transcriptase)

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Viral metagenome

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collection of viral genomes

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ΦX174

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isosahedral virion bacteriophage with circular ssDNA genome with only a few overlapping genes

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Bacteriophage M13

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filamentous phage with helical symmetry that attaches to pilus of host cell, effective clone vector

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Bacteriophage Mu

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temperate phage with ability to replicate via transposition; integration into host genome necessary for lytic & lysogenic development

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Pox viruses

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all replication events occur in cytoplasm instead of nucleus

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Adenovirues

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replication of genome proceeds in leading fashion on both DNA template strands

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Vaccinia virus

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pox virus used as carrier of proteins from pathogenic viruses; elicits strong immune response & stimulates antibody production

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Bacteriophage MS2

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infects E. Coli by attaching to pilus; + ssRNA virus; controls access of host ribosomes to translational start sites on its RNA

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Polyproyein

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occurs in poliovirus; single large protein that self cleaves into about 20 smaller proteins (post-translational cleavage)

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Segmented genome

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present in influenza viruses; multiple pieces of – ssRNA make up the genome

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Antigenic cell

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occurs when a cell is infected with 2 different viral strains that are packaged incorrectly with segments from each of the 2 viruses in progeny

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Rotavirus

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dsRNA virus that causes diarrhea in infants; all replication occurs in nucleocapsids

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Provirus

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integrated genome produced by retroviruses that cannot be removed from host genome

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Hepadnaviruses

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retrovirus example

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Viroids

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infectious RNA molecules with no protein; affect plants

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Prions

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distinct extracellular form consisting solely of protein (no NA)

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Transmissible spongiform encephalopathies (TSEs)

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diseases caused by prions (mad cow)