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58 Cards in this Set
- Front
- Back
RNA Bacteriophages
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Small RNA genome of these bacterial viruses is translated directly and encodes only a few proteins
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What conformation do all bacterial RNA viruses have?
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icosahedral conformation
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Phage MS2
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RNA bacteriophage that infects E. coli
genome of a SS "plus sense" strand RNA can be translated directly upon entry into the host |
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Icosahedral SS DNA Bacteriophages
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a complementary strand of DNA must be synthesized before transcription can occur
only the (+) strand of DNA is packaged in progeny virions |
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OX174 Bacteriophage
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circular SS DNA genome
first genetic element shown to have overlapping genes |
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Filamentous SS DNA Bacteriophages
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have helical symmetry
circular SS DNA genome infect e. coli most studied member is phage M13 |
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intergenic spaces
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spaces in filamentous SS DNA bacteriphage genome that do not encode proteins
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overlapping genes
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1) lysis protein is encoded by a gene that overlaps both the coat protein and the replicase protein
2)parts of the genome are read more than once using different reading frames 3) common in small genomes to allow more efficient use of the limited sized genome |
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Replicative Form (RF)
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cellular DNA always replicates in the DS configuration
on infection, (+) sense viral DNA becomes separated from the protein coat when upon entrance into the cell SS DNA converted to double-stranded molecule |
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Assembly of mature M13 virions
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occurs on the inner surface of the cytoplasmic membrane
end of the M13 virion containing multiple copies of the A-protein is released first with the remainder of the virion following process of assembly is couples with the budding process |
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Bacteriophage T7
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DS DNA bacteriophage
have linear genome and icosahedral symmetry infect e.coli and shigella has some overlapping genes |
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How is virus multiplication regulated on the T7 chromosome?
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order of the genes on the T7 chromosome influences the regulation of virus multiplication
T7 DNA injected into the host cell with the genes at the "left end" of the genetic map entering first |
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Mu ("mutator" phage)
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DS Transposable DNA bacteriophage
introduces mutations into the genome of host genome it is incorporated into temperate virus "like lambda" linear genome with icosahedral symmetry replicates as "transposable element" (TE) |
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Order of transcription of T7
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T7 uses host RNA polymerase first to transcribe "early proteins" that:
1) protect the virus from digestion by host RE 2) turn off transxription of host genes 3) provide T7 RNA polymerase for recognizing phage promoters that will lead to the transcription of later stage T7 genes |
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Transposable Elements
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1)sequences of DNA that can move from one location on their host genome to another as discreet genetic units
2) found in both prokaryotes and eukaryotes 3) play an important role in genetic variation |
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Transposase
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an enzyme that Mu uses to replicate its DNA by transposition
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Variable end
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sequence variation in every Mu occurs at this site
results from where the cut is made in the DNA (Mu virion is packaged into the icosahedral head) each virion is thus genetically unique as result of this |
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G region
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either (+) [forward] or (-) [inverted]
orientation of this detrmines the kind of tail fibers this phage possesses as a means of adsorption to the host cell ultimately determines the host range of Mu |
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Replication of Mu
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1) cuts made using transposase
2) involves DNA at the cut and Mu insertion site 3) 5 bp duplication is typical of Mu replication process |
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Most common morphologies of Archae viruses
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1) Icosahedral head/tail
2) unusual spindle shaped (not seen in bacteria) |
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Archae viruses (3)
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1) all archae viruses have DS DNA genomes
2) some are linear while others are circularly permuted 3) genome size of archae viruses is very small |
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Archae virus replication
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1) much less is known compared to viral replication in the bacteria
2) mechanisms are probably similar to those seen in the bacteria 3) little is known regarding the effects archae viruses have on teh genomes of their hosts |
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Differences between prokaryotic and eukaryotic viruses (3)
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1) Prokaryotes process of transcription and tranlation are coupled while eukaryotes are not
2) prokaryotes can translate polycistronic mRNA while eukaryotic cells cannot 3) transcription occurs in nucleus and translation occurs in cytoplasm in eukaryotes |
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Plant Viruses
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1) first one found was Tobacco Mosaic Virus (TMV)
2) has helical symmetry 3) single copy of (+) strand RNA genome 4) genome only encodes 4 proteins |
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Chlorella Virus (Chlorella PBCV-1
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a large, icosahedral virus that has a large DS DNA genome
infects its host and replicates in a fashion similar to the bacteriophages genomes of chlorella viruses encode several restriction and modification enzymes |
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Chlorella
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type of green algae
can be infected by a virus called PBCV-1 |
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How do the polioviruses and coronaviruses replicate?
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replicated by conversion of the (+) stranded genome into a (-) stranded intermediate from which new (+) strands are synthesized
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What is important about the lipid component of chlorella viruses?
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they are important for infectivity
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Replication of polio virus
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1) begins shortly after infection
2) is catalyzed by RNA replicase 3) takes place in cell cytoplasm |
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RNA replicase uses in polio virus replication
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1) transcribes (+) sense viral RNA into the complementary (-) strand
2) (-) strand is template for repeated transcription of progeny viral (+) strands 3) some of progeny (+) strand may again be transcribed into (-) strand |
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Coronaviruses and SARS
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SS (+) RNA virus
responsible for a variety of respiratory infections in humans and animals larger genome size than polio virus (largest of any known RNA virus) round in shape with glycoprotein spikes protruding outward |
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Negative Strand RNA viruses
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1) RNA genome itself is a (-) stranded RNA
2) the RNA however is not also the mRNA like in poliovirus 3) examples are Rhabdoviruses (rabies) and Orthomyxoviruses (influenza) |
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Rhabdoviruses (3 characteristics)
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1) rod shaped
2) nucleocapsid has helical symmetry 3) enveloped viruses with an extensive lipid envelope surrounding nucleocapsid |
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Replication and assembly of Rhabdoviruses
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1) uses RNA dependent RNA polymerase to covert (-) strand into (+) strand complement
2) RNA is transcribed in the cytoplasm into 2 distinct classes of RNA |
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What two coat proteins are formed during RNA replication of Rhabdoviruses?
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Nucleocapsid and envelope that is coated with glycoproteins
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Orthomyxoviruses
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"myxo" refers to teh fact that these viruses interact with mucus or slime of the cell surface
have envelopes consisting of viral proteins and lipoid derived from host cell nucleocapsid portion of virus is embedded in the envelope |
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Neuraminidase
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is another surface protein that breaks down the sialic acid component of hte host cell membrane
otherwise, sialic acid would block viral assembly or beome incorporated into the mature virus particle |
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What two key enzymes do influenza viruses possess?
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1) RNA dependent RNA polymerase (RNA replicase) [converts (-) stranded genome into a (+) strand
2) RNA endonuclease [cuts a primer form the hots capped mRNA precursors |
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Antigenic Shift
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portions of the RNA genome from two genetially distinct strains of virus simultaneously infecting the same cell are reasssorted
rearranges the surface proteins from those of the original viruses these surface proteins ar eth emajor graget of the immune systems antibodies |
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Antigenic Drift
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occurs when hemagglutinin and neuraminidase proteins become subtly altered by mutations
affects how antibodies are able to recognize virus usually less dangerous than the effects caused by genetic shift |
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Reoviruses
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are a family of animal viruses
include rotavirus which can cause respiratory and intestinal infections consists of linear DS RNA they contain an RNA dependent RNA polymerase |
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Two steps in Reovirus Replication
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1) first step is to use the RNA dependent RNA polymerase to make (+) sense mRNA from the (-) strand template
2) mRNA is capped, methylated and then translated |
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Polyomaviruses
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some types induce tumors in animals (simian virus 40) [SV40]
has no enzymes genome is a supercoiled circular DS DNA molecule |
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SV40 in the host cell
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nucleic acid is replicated in the nucleus
proteins are replicated in the cytoplasm final assembly of the SV40 virion occurs in the nucleus |
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Genetic Map of SV40 genome
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1) replication of these viruses divide dinto early and late stages
2) early stage- early genes transcribed 3) late stage- late genes transcribed important mRNA's are transcribed during both stages |
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Polyomaviruses
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can cause cancer when the viral DNA becomes integrated into a nonpermissive host DNA
can lead to inhibition of cell growth and eventual transformation of a cell to a tumorigenic state |
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Herpesviruses
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large group of DS DNA viruses
cause a variety of diseases in humans and animals ability to remain latent in teh body for long periods and become active under stress conditions |
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General Features of Herpesviruses
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1) structurally complex and consist of 4 distinct morphological units
2) center of virus is called the core (consists of linear DS DNA) 3) icosahedral symmetry of nucleocapside |
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Tegument
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fibrous layer outside the nucleocapsid in herpesviruses
surrounded bya n envelop that has spikes on teh outer surface |
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Herpes infection and replication
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virus attaches to receptors of host cell
nucleocapsid then released into cell transport to the nucleus where viral DNA is uncoated following infection 3 classes of mRNA are produced immediate, delayed, late |
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Pox Virus
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linear DS DNA
among the most complex and largest of animal viruses virus DNA is syntehsized outside the host cell nucleus first virus to be studied in detail and to have a vaccine developed for |
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Adenoviruses
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linear DS DNA
first isolated from human tonsils and adenoids glands cause mild respiratory infection replication and DNA syntehsis occurs in the host cell nucleus |
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Two viruses that use reverse transcriptase to replicate
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1) Retroviruses- have RNA genomes
2) Hepadnaviruses- have DNA genomes |
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Retroviruses
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have two copies of RNA genome and several enzymes
need these enzymes b/c their RNA genome is not used directly as mRNA instead, one of the copies of the genome is coverted to DNA by reverse transcriptase and is integrated into the host cell genome |
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3 enzymatic activities of Reverse Transcriptase
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1) synthesis of DNA from an RNA template
2) Synthesis of DNA from a DNA template 3) Ribonuclease H activity that degrades the RNA strand of a DNA:RNA hybrid |
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Hepadnaviruses
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hepatitis B virus
very small genomes/structurally use overlapping enese effectively is replicated through an RNA intermediate |
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DNA genomes of Hepadnaviruses
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only partially DS DNA
(+) DNA strand is incomplete and both (+) and (-) strands have gaps both strands are held together in a circular form by H-bonding of complementary base pairs |
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Viral DNA polymerase possesses these three functions
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1) DNA Polymerase Activity
2) Reverse Transcriptase Activity 3) Ability to function as a protein primer on the (-) DNA strand |