Unit 2 Viral Replication Strategies Flashcards Preview

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Flashcards in Unit 2 Viral Replication Strategies Deck (57):

Viruses are very ______ to a host cell/organism

What is an exception?


Influenza, it can target bird or swine in some strands


The possible range of interactions a virus can have with different host cells is dictated by the interaction between _______ and host cell receptor molecules

Viral Attachment Proteins


It is not wise to block receptors on cells that are used in viral infection because they have important cellular _____

Therefore, we try to block the______




E. coli has many strains belonging to the same species, and these have antigenic variation for different surface proteins. Phage T2 and phage PP01 can infect different strains (K12 and O157), but what happens when you switch the surface proteins of the phages?

They infect the other strain that they couldn't originally infect but that the other could.

Thus, host range is determined by phage attachment proteins (in this case, tail fibers)


Bacteriophages typically have what type of attachment proteins?

Enveloped viruses, like influenza, typically have what type of attachment proteins?

Non-enveloped (naked) viruses can have what two types of attachment proteins?

Tail fibers

Spike Proteins

Spike extending from viral capsid and attachment proteins that are a part of the viral capsid (capsomere proteins)


Can strain specificity exist within a single species?

What example of disease was used in class?

Explain what scientists observed

What human disease is a good example of this?


Mouse Hepatitis Virus

Mice with the Bgp1a receptor on host cells got infected with MHV while those without Bgp1b did not get infected. The small change in shape did not allow the attachment fibers to bind



Influenza is what type of virus?

What type of attachment protein does it have? What's its name?
What type of capsid structure is it?


Spike protein, hemaglutinin(HA)



By what process does influenza enter the host cell?

What structure forms around the virus?




What structure helps beind the viral envelope and the plasma membrane of the host cell during entry of enveloped viruses?

Fusion peptide


What causes the endosome to break down and expose the viral membrane fusion peptide in the entry of enveloped viruses into host cells. It causes a change in shape of the protein (hemaglutinin in the influenza example)

What occurs after?



Low pH (acidification)

Membrane fusion

Release of viral nucleocapsid



In the case of HIV, an enveloped virus, what is the surface protein it binds to on the host cell?

What are the spike proteins on the surface of HIV called?


gp120 and gp41


Which HIV spike protein binds to CD4?

What occurs next?

This triggeres a conformation change, what becomes exposed? It helps facilitate membrane fusion

After binding, this spike protein becomes exposed and interacts with the host membrane

What occurs next


It bonds to the co-receptor

Fusion peptide


gp41 folds and brings the viral envelope and PM together


What does Fuzeon do to block HIV?

It blocks gp41 folding in order to inhibit fusion


How is fuzeon imperfect?

It only lowers the amount of HIV, it is not perfect
It has to be in the right place at the right time


Viruses that enter bacteriophages are typically what kind of structure?

What cuts the peptidoglycan wall of the bacteriophage?

The virus can be ___ or _____

Does the capsid enter the bacteriophage?



Lytic or Lysogenic

No, the genome is injected into the bacteriophage and the capsid remains outside of it


Plant viruses often require damage induced by insects to infect the plants cells because or tough.

what can cause this damage?

cell walls

Weather, insects, humans


Each virus may use a different method for viral uncoating, but the viral genome must be inserted into the host cell.

This exception we went over in class injects its genome into the host cell with the capsid staying on the outside of the host cell, pretty unusual.



When poliovirus infects human cells, the poliovirus receptor on the host cell attaches to the caspid, and a conformational change causes it to be lost and replaced by a receptor from the virus that forms a pore in the host cell. What are the names of these proteins?

After the aforementioned process, the genome is inserted into the host cell

VP4 and VP1


What classes can DNA viruses be?

What classes can RNA viruses be?

What are these classes based upon?

What do those depend upon?

Class 1, 2, and 7

Class 3,4,5,6

Replication strategies

Replication strategies depend upon genome type


In class 1, what is the genome?

What is used to replicate this?

What occurs next?

which strand is read to make the mRNA?

Double stranded DNA

DNA polymerase


the negative strand is read to make +mRNA


In class 2, what is the genome?

For replication, what must be formed first?

For transcription, what must be formed first?

What type of mRNA is formed from transcription?

What strand is read, then?

Single stranded DNA (+ or -)

Temporary double stranded DNA intermediate

Temporary double stranded DNA intermediate

Always +mRNA for mRNA in all classes

(-) DNA strand


In class 7, what is the genome?

For replication, what is formed first?

What occurs next for replication? What carries this process out?

For mRNA formation, what occurs next?

Which strand is read to make the RNA?

Double stranded DNA

Single stranded RNA (+)

Reverse transcription. Reverse transciptase (a viral enzyme)


the negative strand is read to make +mRNA


In class 3, what is the genome?

For transcription, which strand is used to make the

For genome replication, what is made first?

Double stranded mRNA

The minus strand is used to make +mRNA

+mRNA intermediate


In class 4, what is the genome?

For mRNA formation, what occurs?

For genome replication, what is made first?

Single stranded mRNA (+)

the +mRNA genome is used directly to make proteins

Double stranded RNA intermediate


In class 5, what is the genome?

For mRNA formation, what occurs?

For genome replication, what is made first?

Single stranded mRNA (-)

transcription to +mRNA

double stranded mRNA


For class 6, what is the genome?

For mRNA formation, what occurs first?

For genome replication, what occurs first

Single stranded mRNA (+)

Reverse transcription to double stranded DNA. Transcription to +mRNA follows from the negative DNA strand

Reverse transcription to double stranded DNA. the replicated genome is formed from the negative strand


During the replication of typical eukaryal DNA viruses, the DNa goes to the nucleus after the enzymes in the cytoplasm release them from the capsid. What do they do there?

Where do they go after and for what purpose?

Where do the resulting structures go?


The transcribed viral DNA goes back to the cytoplasm for translation of proteins

The proteins go back into the nucleus


During the replication of typical eukaryal DNA viruses, once the proteins have been formed from the viral genome and returned to the nucleus, what happens?

What other structures are on the virion?

Assembly of the capsid with the replicated genome and exit

Spike proteins


What was the example of atypical replication of eukaryal DNA viruses?

What is unique about it?


transcription takes place in the cytoplasm, so it brings its own viral RNA polymerase


In the replication of the poxvirus, there are two types of genes. What are they?

Early and Late genes


This poxvirus gene leads to DNA polymerase after translation

Early Genes


This poxvirus gene leads to proteins for capsid contstruction

Late Genes


In the replication of positive sense RNA viruses, what is created initially by translation (this occurs sometimes, can also come packaged)

What does it make?

RNA dependent RNA polymerase

The complimentary -RNA strand


In replication of positive sense RNA viruses, if there is no envelope, what might occur?

Lysing by weakening of the cell membrane


In the replication of negative sense RNA, what must always occur?

Once the above occurs, protein translation or genomic replication can occur

Production of +RNA


In the replication of retroviruses, what is the first thing that occurs to the genome once inside the nucleus?

Note that spike proteins are eventually made too

Reverse transcription


In the replication of retroviruses, once the double stranded DNA has been made by reverse transcription, the DNA and viral protein integrase go into the nucleus and insert the DNA into the chromosome at a random positive. What is the viral DNA that has been inserted called? It doesn't have to cut itself out.



Where do spike proteins made coded for by the viral genome but made by the host cell go?

The host cells plasma membrane


What breaks down the packaging of enveloped viruses liked HIV?

Enzymes in the cytoplasm. There is polymerase in the cytoplasm which allows the DNA to be coded for


What two things occur for both lytic and lysogenic bacteriophages?

Assembly and penetration


A virulent bacteriophage is...

A temperate bacteriophage is...




What does the lytic virus code for that the host cell produces that eventually causes the cell to break and release mature phages?



The lysogenic bacteria joins the host cell DNA to make a

How does it replicate

What might cause the prophage to become permanently integrated?


It replicates when the host cell divides



With a bacterial provirus, what causes excision and return to the lytic cycle?

The environment (UV light, slowing of replication)

AKA bad environments


What two things are largely influential in determining whether a bacteriophage enters the lytic or lysogenic phase?

C1 and Cro


When there is a high amount of Cr1 promoter being expressed by RNA polymerase, creating the Cro repressor protein, which cycle occurs?



When there is a high amount of Cro promoter being expressed by RNA polymerase, creating the C1 repressor protein, which cycle occurs?

Lytic Phase


The most common type of viral assembly is fast and cheap from an energetic perspective



These structures of viruses may interact with packaging sequences on the viral genome to coalesce around the nucleic acid (ex, tobacco mosaic virus)

Additionally, like the poliovirus, empty ____ may partially form then have the viral genomes inserted into them

Capsid proteins



This means viral exit from the cell

Is the mechanism universal to all viruses?




This type of viruses put viral proteins (spikes) in the host membrane, dock to them, and bud out of the cell, taking a portion of the plasma membrane with them

Enveloped Viruses


This virus types almost always exit the cell by lysis

This virus type may move from cell to cell by specific cytoplasmic interactions.

What are the cytoplasmic connections called?

Naked Viruses

Plant viruses (they move within one plant)



How do plant viruses move from one plant to another?

Disruption of the cell wall structures, often by insects


This antiviral drug is a nucleoSIDE analog used for HIV



What is different about AZT that allows it to work?

What does it inhibit?

Why doesn't inhibit DNA polymerase?

It has an N2 group attached to the 3' carbon instead of OH

Reverse Transcriptase

Reverse Transcriptase has a higher affinity for it.


Another good antiviral that works by p[reventing the activity of the enzyme that helps a new virus detach from the infected cell



Which protein helps the flu virus get into the host cell and eventually gets stuck to the receptor requiring cleaving

This surface protein cleaves the aforementioned protein from the cell receptor

Which does tamiflu act on?