0127100930 - Mfm Ii - Virus Multiplication (Colle)

Front 1

What are the 6 basic steps of a virus life cycle?

Back 1

1. attachment
2. penetration
3. uncoating
4. biochemical replication
5. assembly
6. release

Front 2

In regard to viral attachment, where is the receptor located that allows the virus to attach?

Back 2

the receptor is always on the host cell

Front 3

How does the Polio virus attach to a host cell?

Back 3

VP1 attachment protein on the virus attaches to the Ig Superfamily protein on primate cells

Front 4

Can a virus replicate in an organism in which the specific receptor does not exist on the host cell to allow attachment?

Back 4

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

Front 5

What are the three methods in which viruses penetrate animal cells?

Back 5

1. viropexis
2. fusion
3. direct penetration

Front 6

What is viropexis?

Back 6

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)

Front 7

What is a viral example of viroplexis?

Back 7

Influenza
Amantidine blocks pH lowering that allows for internal release of endocytosed virion.

Front 8

What is fusion?

Back 8

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

Front 9

What is direct penetration?

Back 9

a generally unknown penetration mechanism that leads to the complete virus being in the cytoplasm

Front 10

What is a viral example of direct penetration?

Back 10

adenovirus

Front 11

What does viral uncoating produce?

Back 11

infectious viral particle. so there is no infectious particle until after the uncoating process occurs.

Front 12

What is temporal regulation?

Back 12

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

Front 13

What are immediate early (IE) genes?

Back 13

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.

Front 14

What are early genes?

Back 14

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

Front 15

What is dna replication in temporal regulation?

Back 15

Third stage of temporal regulation:
simply replicating all of the viral genetic material

Front 16

What are late genes?

Back 16

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

Front 17

What three replication strategies do RNA viruses use?

Back 17

1. positive-stranded - genome is mRNA
2. negative-stranded - genome will be transcribed into mRNA
3. retro - RNA is reverse transcribed into DNA

Front 18

Where does capsid assembly occur and how does it occur?

Back 18

When the biochemical components are available they will self-assemble.

DNA capsids will occur in nucleus
RNA capsids will occur in cytoplasm

Front 19

What are the three methods of viral release?

Back 19

1. lysis of cell
2. slow release via vacuoles, reverse phagocytosis
3. budding of individual virions into EC space

Front 20

What are two examples of lysis of cell to release virus?

Back 20

1. picornaviridae causing polio simply engorges the cell until it pops
2. adenoviridae causing adenovirus releasees the Adeno Death Protein (ADP) that causes lysis

Front 21

What are details of the positive-stranded RNA virus replication?

Back 21

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

Front 22

What other strategy is used in some cases of positive-stranded RNA replication?

Back 22

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

Front 23

What are the details of the non-segmented negative-stranded RNA virus replication?

Back 23

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

Front 24

What are the details of segmented negative-stranded RNA virus replication?

Back 24

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.

Front 25

What virally unique molecule is used in retrovirus replication?

Back 25

RNA dependent DNA polymerase, aka reverse transcriptase which copies viral RNA to DNA

Front 26

What is a provirus?

Back 26

The DNA product of retrovirus replication that injects itself into the host genome and is replicated by the hosts normal biochemical replication machinery. Sneaky.

Front 27

What are the details of retrovirus replication?

Back 27

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