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58 Cards in this Set

  • Front
  • Back
RNA Bacteriophages
Small RNA genome of these bacterial viruses is translated directly and encodes only a few proteins
What conformation do all bacterial RNA viruses have?
icosahedral conformation
Phage MS2
RNA bacteriophage that infects E. coli

genome of a SS "plus sense" strand RNA

can be translated directly upon entry into the host
Icosahedral SS DNA Bacteriophages
a complementary strand of DNA must be synthesized before transcription can occur

only the (+) strand of DNA is packaged in progeny virions
OX174 Bacteriophage
circular SS DNA genome

first genetic element shown to have overlapping genes
Filamentous SS DNA Bacteriophages
have helical symmetry

circular SS DNA genome

infect e. coli

most studied member is phage M13
intergenic spaces
spaces in filamentous SS DNA bacteriphage genome that do not encode proteins
overlapping genes
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
Replicative Form (RF)
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
Assembly of mature M13 virions
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
Bacteriophage T7
DS DNA bacteriophage

have linear genome and icosahedral symmetry

infect e.coli and shigella

has some overlapping genes
How is virus multiplication regulated on the T7 chromosome?
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
Mu ("mutator" phage)
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)
Order of transcription of T7
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
Transposable Elements
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
an enzyme that Mu uses to replicate its DNA by transposition
Variable end
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
G region
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
Replication of Mu
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
Most common morphologies of Archae viruses
1) Icosahedral head/tail

2) unusual spindle shaped (not seen in bacteria)
Archae viruses (3)
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
Archae virus replication
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
Differences between prokaryotic and eukaryotic viruses (3)
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
Plant Viruses
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
Chlorella Virus (Chlorella PBCV-1
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
type of green algae

can be infected by a virus called PBCV-1
How do the polioviruses and coronaviruses replicate?
replicated by conversion of the (+) stranded genome into a (-) stranded intermediate from which new (+) strands are synthesized
What is important about the lipid component of chlorella viruses?
they are important for infectivity
Replication of polio virus
1) begins shortly after infection

2) is catalyzed by RNA replicase

3) takes place in cell cytoplasm
RNA replicase uses in polio virus replication
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
Coronaviruses and SARS
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
Negative Strand RNA viruses
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)
Rhabdoviruses (3 characteristics)
1) rod shaped

2) nucleocapsid has helical symmetry

3) enveloped viruses with an extensive lipid envelope surrounding nucleocapsid
Replication and assembly of Rhabdoviruses
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
What two coat proteins are formed during RNA replication of Rhabdoviruses?
Nucleocapsid and envelope that is coated with glycoproteins
"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
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
What two key enzymes do influenza viruses possess?
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
Antigenic Shift
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
Antigenic Drift
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
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
Two steps in Reovirus Replication
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
some types induce tumors in animals (simian virus 40) [SV40]

has no enzymes

genome is a supercoiled circular DS DNA molecule
SV40 in the host cell
nucleic acid is replicated in the nucleus

proteins are replicated in the cytoplasm

final assembly of the SV40 virion occurs in the nucleus
Genetic Map of SV40 genome
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
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
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
General Features of Herpesviruses
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
fibrous layer outside the nucleocapsid in herpesviruses

surrounded bya n envelop that has spikes on teh outer surface
Herpes infection and replication
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
Pox Virus
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
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
Two viruses that use reverse transcriptase to replicate
1) Retroviruses- have RNA genomes

2) Hepadnaviruses- have DNA genomes
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
3 enzymatic activities of Reverse Transcriptase
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
hepatitis B virus

very small genomes/structurally

use overlapping enese effectively

is replicated through an RNA intermediate
DNA genomes of Hepadnaviruses
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
Viral DNA polymerase possesses these three functions
1) DNA Polymerase Activity

2) Reverse Transcriptase Activity

3) Ability to function as a protein primer on the (-) DNA strand