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Virology > Virus Replication > Flashcards

Virus Replication Flashcards

1
Q

permissive cell

A

cell in which a virus is able to replicate; cell machinery supports replication of the virus

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2
Q

non-permissive cell

A

cells in which a factor or factors necessary to viral reproduction is not present or one detrimental to viral reproduction is present (e.g. absence of appropriate receptors)

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3
Q

MOI

A

multiplicity of infection; # virions added per cell during infection

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4
Q

one step virus growth curve

A

collect aliquots of cells and cell-culture fluid at different time intervals for measuring titer of intracellular and extracellular virions

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5
Q

adsorption

A

virus attaches to and enters cells, and the titer of free virus in the medium may actually decline

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6
Q

eclipse period

A

time interval between uncoating and appearance, intracellularly, of first infectious progeny virions

  • no infectious virus detected during this time
  • 2-12 hours for most virus families
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7
Q

latent period

A

time before new infectious virus appears in the medium (time from uncoating to just prior to release of first extracellular virions)
- no extracellular virions detected in this phase

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8
Q

burst size

A 
# infectious virions released per average cell 
*height of curve
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9
Q

Which step of virus replication is the “kiss of death”?

A

attachment

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10
Q

receptor

A

structure on surface of a cell (or inside) that selectively receives and binds a specific substance, and mediates its entry or action into the cell

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11
Q

Is binding to a cellular receptor always sufficient for infection?

A

No, sometimes an additional cell surface molecule (co-receptor) is required for entry

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12
Q

Whats an example of a virus that uses more than one host cell receptor?

A

HIV

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13
Q

What are the possible methods of virus penetration?

A
  • endocytosis
  • surface fusion
  • pore-mediated penetration
  • antibody-mediated penetration
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14
Q

receptor-mediated endocytosis occurs with which kind of viruses?

A

naked viruses and most enveloped viruses

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15
Q

During endocytosis, what is the vesicle coated in?

A

clathrin (CCP)

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16
Q

What acts to pinch off the clathrin-coated pit from the host membrane to create a clathrin-coated vesicle (CCV)?

A

dynamin

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17
Q

Once the clathrin is removed and the vesicle delivers viral content to endosomes, what has to happen for the viral genome to be released?1

A

The pH in the endosome changes to acidic

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18
Q

How can the viral genome be released for non-enveloped viruses

A
  • lysis when a viral capsid induces rupture of endosomal membrane
  • induce local permeabilization of host endosomal membrane to allow virus capsid penetration into the cytoplasm
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19
Q

Other types of receptor-mediated endocytosis (just know names)

A
  • caveolin-mediated endocytosis of virus by host (specialized lipid rafts)
  • clathrin and caveolin independent endocytosis of virus by host
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20
Q

Membrane fusion (surface fusion) can only occur for which types of viruses?

A

enveloped viruses only

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21
Q

After surface fusion occurs, what remains on the cell surface and is antigenic?

A

viral glycoproteins -> cell can become target of immune system of the host

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22
Q

What is ADCC?

A

antibody-dependent cell mediated cytotoxicity

  • antibody binds antigens on target cell
  • Fc receptors on NK cell recognize
  • NK cell kills target cell
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23
Q

Which protein acts to facilitate membrane fusion?

A

fusion protein (F)

  • pH independent in HIV and measles
  • pH dependent in influenza virus
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24
Q

What type of viruses use pore-mediated penetration?

A

non-enveloped viruses

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25
Q

antibody mediated attachment and penetration

A
  • FIP virus
  • enters host macrophage by attachment of spike proteins to CD13 receptor
  • antibodies against spike proteins can’t clear the virus, so when they bind spike proteins they facilitate viral entry through antibody IgG-Fcgamma receptor
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26
Q

What happens during the eclipse period so that the virion can no longer be detected?

A

viral uncoating

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27
Q

What in the endosome promotes fusion of the virus envelope with the endosomal membrane to uncoat the virus?

A

low pH

28
Q

Where does virus uncoating occur?

A

nuclear membrane

*poliovirus begins uncoating after binding to external receptor but not completely uncoated until inside the cell

29
Q

Example of a virus in which uncoating requires a complex series of steps involving both host and viral gene products?

A

poxvirus

30
Q

2 viruses in which first stages of the viral replication cycle actually occur inside the capsid?

A

retroviruses and reoviruses

31
Q

Which step causes the loss of infectivity of virions?

A

uncoating

32
Q

What is the role of DNA-dependent RNA polymerase?

A

transcribes the (-) DNA strand to form (+) mRNA and then translates that to create a viral protein

33
Q

What is the role of DNA-dependent DNA polymerase?

A

Copies both + and - strands to form dsDNA viral genome that can be passed down

34
Q

replication of ssDNA

A
  • DNA-dependent DNA polymerase copies + strand to form dsDNA intermediate
  • DNA-dependent RNA polymerase transcribes (-) strand to form (+) mRNA and translates that to viral protein
  • DNA-dependent DNA polymerase copies the (-) DNA strand to form (+) ssDNA viral genome
35
Q

replication of dsRNA

A
  • RNA dependent RNA polymerase copies both strands to form viral genome
  • RNA dependent RNA polymerase transcribes (-) strand to form (+) mRNA and translates to viral protein
36
Q

replication of ssRNA (-)

A
  • RNA dependent RNA polymerase transcribes (-) strand to (+) mRNA and translates to viral protein
  • RNA dependent RNA polymerase copies (-) strand to form (+) ssRNA
  • RNA dependent RNA polymerase copies (+) strand to form (-) ssRNA viral genome
37
Q

replication of ssRNA (+)

A
  • (+) ssRNA directly translated into viral protein
  • RNA dependent RNA polymerase copies (+) strand to (-) ssRNA
  • RAN dependent RNA polymerase copies (-) strand to form (+) ssRNA viral genome
  • RNA dependent RNA polymerase also transcribes (-) ssRNA to form (+) ssRNA and translates to viral protein
38
Q

Why is reverse transcriptase necessary for replication of retroviruses?

A

They have to synthesize cDNA which will integrate into the host genome

  • begin with (+) ssRNA RT copy to form (-) ssDNA which is then copied to form (+) ssDNA -> come together to form cDNA
  • the cDNA then used to form (+) ssRNA both for genome and protein production
39
Q

What is special about Hepadnaviridae?

A
  • have circular dsDNA which is incomplete and require RT to form RNA intermediate to replicate
  • hepatitis B is most well-known

*probably arise from a deletion from a retrovirus !

40
Q

What has to happen to pre-RNA before it can be translated?

A
  • capping

- addition of 3’ poly-adenylated tails

41
Q

How are caps synthesized?

A
  • by host cell enzymes (retroviruses, adenoviruses)
  • by viral enzymes (poxviruses, reoviruses)
  • cap snatching: steals caps from host mRNAs (influenza)
42
Q

What is capping?

A

addition of 7-methylguanosine to 5’ end of RNA

43
Q

Why does capping occur?

A
  • stability of mRNA
  • binding of mRNA to ribosomes
  • mark mRNA as “self”
44
Q

Why is adding a tail important?

A

polyA tails interact with polyA-binding protein which is important for translation

45
Q

What is the major signal for 3’ cleavage to add a tail?

A

AAUAAA

*cleavage occurs 10-35 nucleotides downstream from signal

46
Q

What is splicing?

A

RNA splicing is process that removes introns and joins exons in a primary transcript

47
Q

What is an exon?

A

portion of a gene that codes for amino acids

48
Q

What is an intron?

A

portion of a gene that doesn’t code for amino acids (bye felicia)

49
Q

constitutive splicing

A

every intron spliced out and every exon spliced in

50
Q

alternative splicing

A

all introns spliced out and only select exons spliced in -> mRNAs that have different coding info derived from a single gene

51
Q

monocistronic mRNA

A

encodes one polypeptide

*one ORF and single initiation and stop codon

52
Q

polycistronic mRNA

A

encodes several polypeptides; multiple ORF

53
Q

How does polycistronic mRNA become functional protein?

A
  1. translated to polyprotein and protease forms functional proteins
  2. endonuclease forms monocistronic mRNAs which are translated into functional proteins
54
Q

Is polyprotein functional?

A

No -> need protease to separate into individual functional proteins

  • occurs in Flaviviridae
  • HIV has protease inhibitors -> proteins won’t be free and functional
55
Q

Important viral proteins include:

A
  • enzymes
  • structural proteins
  • viral nonstructural proteins
  • regulatory proteins
  • inhibitors
56
Q

Where does assembly and maturation occur?

A
  • nucleus
  • cytoplasm
  • plasma/cell membrane (most enveloped viruses)
57
Q

How do naked virions release progeny?

A

lysis of host cell

58
Q

How do enveloped virions release progeny?

A

budding

59
Q

budding

A
  • proteins that are to become spikes of virus attach to cytoplasmic membrane
  • matrix protein coats inside of cytoplasmic membrane
  • nucleocapsid enclosed by viral envelope, composed of host’s cytoplasmic membrane
  • pinches off
60
Q

Which viruses mature by budding through membranes of Golgi or ER?

A 
Flaviviruses
Arteriviruses 
Coronaviruses 
Bunyaviruses 
*vesicles with virus then migrate to plasma membrane and are relased by exocytosis
61
Q

replication of retroviruses

A
  1. enter cell and RT RNA -> DNA
  2. integrase puts viral DNA into host genome
  3. transcription to viral RNA
  4. translation to viral proteins
  5. budding to form mature virions
62
Q

extracellular spread of viruses

A

released viruses in extracellular environment and travel to new host cell -> same replication cycle repeats

63
Q

intercellular spread of viruses

A
  • spread cell to cell without contact with extracellular milieu -> rapid virus dissemination, evasion of immune system, persistent infections

HIV, herpesvirus, measles

64
Q

types of intercellular transmission of viruses

A
  1. cell-cell plasma-membrane fusion followed by movement of infectious viral material into uninfected target cell (herpesvirus, paramyxovirus, retrovirus)
  2. passage of virions across tight junction (herpesvirus)
  3. movement of virions across neural synpase (rabies)
  4. viral induction of actin or tubulin containing structures (poxvirus)
  5. viral subversion of actin containing structures, form filopodial bridges (retroviruses)
  6. membrane nanotube subversion (HIV1)
  7. virological synapses (retroviruses)
65
Q

nuclear spread of virus genome

A

viral genome integrated into host cell genome and passed down to next progeny or generation of host cells (retrovirus)

Virology (16 decks)

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