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27 Cards in this Set

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What are the 6 basic steps of a virus life cycle?
1. attachment
2. penetration
3. uncoating
4. biochemical replication
5. assembly
6. release
In regard to viral attachment, where is the receptor located that allows the virus to attach?
the receptor is always on the host cell
How does the Polio virus attach to a host cell?
VP1 attachment protein on the virus attaches to the Ig Superfamily protein on primate cells
Can a virus replicate in an organism in which the specific receptor does not exist on the host cell to allow attachment?
YES! if the virus finds another way into the cell, then it is possible for replication to occur. this happens outside of the viruses normal life cycle, though. there has to be external intervention
What are the three methods in which viruses penetrate animal cells?
1. viropexis
2. fusion
3. direct penetration
What is viropexis?
a method of penetration that is basically receptor-mediate endocytosis:
1. virus attaches to host cell receptor
2. plasma membrane of the host cell engulfs and internally blebs into cell vesicle
3. pH change causes virus uncoating mechanism by removal of the envelope, fusion of the envelope with the vacuole membrane, or conformational changes release non-enveloped capsids into the cytoplasm

(pic)
What is a viral example of viroplexis?
Influenza
Amantidine blocks pH lowering that allows for internal release of endocytosed virion.
What is fusion?
A type of viral penetration in which when the virus interacts with the host cell receptor that causes the viral envelope to fuse with the plasma membrane -> capsid is released into cytoplasm
What is direct penetration?
a generally unknown penetration mechanism that leads to the complete virus being in the cytoplasm
What is a viral example of direct penetration?
adenovirus
What does viral uncoating produce?
infectious viral particle. so there is no infectious particle until after the uncoating process occurs.
What is temporal regulation?
DNA viruses use this type of biochemical replication which is a cascade viral gene expression. It occurs in 4 phases:

1. immediate early gene expression
2. early gene expression
3. dna replication
4. late gene expression
What are immediate early (IE) genes?
First stage of temporal regulation:
Viral gene transcription factors that bind to cellular promoters to initiate cell transcription. Kick start cell to get into cell replication cycle.
What are early genes?
Second stage of temporal regulation:
genes required for viral replication. after IE genes activate cell cycle, early genes shut down host gene synthesis and initiate viral gene synthesis
What is dna replication in temporal regulation?
Third stage of temporal regulation:
simply replicating all of the viral genetic material
What are late genes?
Fourth and final stage of temporal regulation:
the final genes that are replicated in temporal regulation that produce structural and assembly proteins to form capsids and envelopes
What three replication strategies do RNA viruses use?
1. positive-stranded - genome is mRNA
2. negative-stranded - genome will be transcribed into mRNA
3. retro - RNA is reverse transcribed into DNA
Where does capsid assembly occur and how does it occur?
When the biochemical components are available they will self-assemble.

DNA capsids will occur in nucleus
RNA capsids will occur in cytoplasm
What are the three methods of viral release?
1. lysis of cell
2. slow release via vacuoles, reverse phagocytosis
3. budding of individual virions into EC space
What are two examples of lysis of cell to release virus?
1. picornaviridae causing polio simply engorges the cell until it pops
2. adenoviridae causing adenovirus releasees the Adeno Death Protein (ADP) that causes lysis
What are details of the positive-stranded RNA virus replication?
1. mRNA genome is translated into huge "polyprotein"
2. polyprotein is cleaved into functional proteins that serve as template
3. template produces a negative strand which serves as a "replicative intermediate"
4. RI is the template to make positive daughter strands
5. structural and non structural proteins assemble into mature virus
What other strategy is used in some cases of positive-stranded RNA replication?
somtimes there is more than one polyprotein made, which then one is used for daughter genomic material and the other is used for capsid structural protein synthesis.

the capsid synthesis involves translation of subgenomic mRNA that was produced from the replicative intermediate which produces exclusively structural proteins
What are the details of the non-segmented negative-stranded RNA virus replication?
1. RNA genome is transcribed into several mRNA by use of virally inherent RNA polymerase, aka transcriptase (the virus brings this in with it)
2. mRNA produced is translated into several protein templates
3. template produces a positive strand which serves as a "replicative intermediate"
4. RI is the template to make negative daughter strands
5. structural and non structural proteins assemble into mature virus
What are the details of segmented negative-stranded RNA virus replication?
the difference here is that the genome is broken up into RNA segments that must all be individually transcribed and translated. so the process is the same as non-semgented, except it much occur individual times for each segmented genomic component.
What virally unique molecule is used in retrovirus replication?
RNA dependent DNA polymerase, aka reverse transcriptase which copies viral RNA to DNA
What is a provirus?
The DNA product of retrovirus replication that injects itself into the host genome and is replicated by the hosts normal biochemical replication machinery. Sneaky.
What are the details of retrovirus replication?
1. uniquely diploid negative-stranded RNA is contained in the virus and reverse transcribed into DNA by reverse transcriptionase
2. RNaseH digests RNA bound to DNA
3. single DNA strand is duplicated into a complementary and attached strand
4. double DNA strand is capped with virus promoters and enhancers and mimic eukaryotic molecules
5. foreign DNA is integrated into host genome
6. host replicates viral DNA
7. varied RNA splicing produces viral negative-stranded RNA as well as structural and non structural genes which are assembled as a mature virus