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16. Baltimore classification Flashcards

1
Q

What does Baltimore classification describe

A

Viral replication strategies

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2
Q

How many classes are there

A

7

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3
Q

What happens to ssRNA+/mRNA

A

It synthesizes viral proteins which are then used for genome replication

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4
Q

what enzymes are required for genome replication

A

RNA pol
DNA dip
DNA pol
RNA dip
In 1. and 2.=>DNA pol and dip
In 3. 4. 5.=> RNA pol and dip
In 6.7.=> RNA pol DNA dip; RNA pol RNA dip

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5
Q

What are enzymes for the genesis of ssRNA+

A

FOR ALL: RNA pol DNA dip

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6
Q

What are differences in transcription of replicative class 1

A

dsDNA viruses(Class I)= we have nuclear and cytoplasmic replication
Nuclear replication- viruses use cellular RNA polymerase. Transcription is regulated by cellular and viral TFs, occurring from both strands. Examples: papillomaviridae( cervical cancer) and adenoviridae(colds)
Cytoplasmic replication- viruses encode their own RNA polymerase . Ex: poxviridae(smallpox)

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7
Q

What are differences in replication of replicative class 1

A

We have it for complex and simple viruses
Complex viruses- virial genome replication is mediated by viral DNA-dependent DNA polymerases
They encode proteins for the metabolism of nucleic acids.
Ex:Herpesvidirdae, poxviridae, adenoviridae
Simple viruses
-Viral genome replication is mediated by cellular DNA-dependent DNA polymerases
Ex: poliomaviridae
papillomaviridae

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8
Q

What is poxviridae

A

Largest family of viruses affecting human. Ex: smallpox virus(eradicated)=> lethal disease in 30-50% of cases

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9
Q

What is the ‘‘formula’’ for the first replicating class

A

dsDNA->mRNA

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10
Q

What are characteristics of replicative class 2

A

ssDNA DNA viruses- they synthesize mRNA thanks to the cellular biosynthetic apparatus.

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11
Q

What happens before synthesis of mRNA in replicative class 2

A

ssDNA genomes must be completed to dsDNA in order to be transcribed. The virus replicates its genome in the cell nucleus only during S phase of the cell cycle

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12
Q

Who replicates viral genome in replicative class 2

A

cellular DNA polymerase

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13
Q

What is the ‘‘formula’’ for replicative class 2

A

ssDNA–>dsDNA–>mRNA

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14
Q

What is an example of replicative class 2

A

Parvoviridae. Parvovirus B19 causes minor disease that decreases red blood cell production. It’s small group of viruses whose DNA replication occurs in the nucleus of actively replicating cells

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15
Q

What are general features of RNA viruses

A

-replication and transcription are similar processes
-must encode for RNA-dependent RNA-polymerases
-provided or synthesized quickly
-they work fast
-must provide enzymes for mRNA processing
-pass through a dsRNA intermediate

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16
Q

What are characteristics of replicative class 3

A

dsRNA viruses- they have segmented genome (10-12 segments). These viruses replicate in the cytoplasm with an ssRNA intermediate

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17
Q

What is replication mediated by in replicative class 3

A

Virus-encoded RNA-dependent RNA polymerase that is also essential for genome expression and its encorporated into the infectious virus

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18
Q

What’s the formula for replicative class 3

A

dsRNA–>ssRNA(+)(mRNA)–> gene expression/genome replication(ssRNA-)

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19
Q

What are some examples of viruses from replicative class 3

A

Reoviridae: double icosahedral capsid that can be external and internal. It belongs to rotaviruses that have gastrointestinal forms

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20
Q

What are characteristics of replicative class 4

A

ssRNA(+) viruses- these genomes are said ‘‘infectious’’ as they can be immediately translated by the cellular ribosomes
While genomic RNA encodes early regulatory/replicative proteins, late proteins are encoded generated shorter/subgenomic transcriptssubsequently expressed(separation early and late)

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21
Q

What happens in some cases of replicative class 4

A

Genome consisting of an ssRNA(+) is translated into a polyprotein (no early or late stages)

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22
Q

Where does replicative class 4 replicates

A

In intracellular membrane(viral replication factories) rearrangements with the involvement of a viral RNA dependent RNA polymerase

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23
Q

What are examples of families of replicative class 4

A

-Caliciviridae( Gastroenteritis)
-Picornavirisae(Poliovirus, Hepatitis A, Enteroviruses).They are naked viruses
-Hepeviridae(hepatits E)
-Flaviviridae( Hepatitis C)
-Matonaviridae(Rubella virus)
-Coronaviridae(Severe Acute Respiratory Syndrome SARS)

24
Q

What happens during translation and transcription of the SARS-CoV-2 Genome

A

Nonstructural proteins are synthesized from ORF1 which is broken into two separate frames. Subgenomic RNAs are formed by splicing translational signals from the 5’ genome end to the individual genes

25
Q

How does attachment and entry of SARS-CoV-2 go

A

Entry to a cell through the interaction of its spike protein with the SCE2 cellular receptor. Proteolysis by TMPRSS2 exposes a spike domain that promotes membrane fusion

26
Q

What are steps of replication and viral exit

A
  1. Viral replication occurs in cytoplasmic double membrane vesicles that shelter the genome and concentrate ribonucleotide precursors
  2. Structural proteins are synthesizes on the endoplasmic reticulum
  3. The nucleocapsid protein in complex with positive-strand RNA genome is engulfed by membranes to form cytoplasmic vesicles
  4. That exits the cell by exocytosis
27
Q

what’s the ‘‘formula’’ of replicative class 4

A

(+)ssRNA–>(-)ssRNA–>mRNA

28
Q

What are characteristics of replicative class 5

A

ssRNA(-) viruses can be unsegmented(measles, rabies(Rhaboviridae), Ebola(Filoviridae)) and segmented genome viruses

29
Q

What’s multiplication strategy of negative strand RNA viruses

A

RNA-dependent RNA polymerase enters the cell at the same time the negative-strand RNA genome enters. The genome serves as a template for synthesis of mRNA. Later in the infection, that positive strands then act as templates for replication of thenegative strand genomes

30
Q

What is the ‘‘formula’’ of replication class 5

A

(-)ssRNA–>mRNA

31
Q

What are characteristics of replicative class 6

A

Virus A ssRNA(+) replicated through a DNA/RNA hybrid- viruses contain a diploid RNA+ genome which, once it enters a host cell, is reverse transcribed into dsDNA molecule(provirus) which integrates into the host cell genome

32
Q

What is provirus

A

Virus that integrates into the DNA of a host cell

33
Q

What viral enzymes are involved in replicative class 6

A

Retrotranscriptase and integrase

34
Q

What happens when provirus integrates into host’s genome in replicative class 6

A

It is then transcribed by the host cell’s RNA polymerase II. Thus different classes of subgenomic( single and double spliced) and genomic( unspliced) are expressed

35
Q

What are some viruses from replicative class 6

A

HIV1/2- AIDS
HTLV1-T-cell leukemia

36
Q

What is the ‘‘formula’’ of replicative class 6

A

(+)ssRNA–> DNA/RNA hybrid–>dsDNA–>mRNA

37
Q

What are characteristics of replicative class 7

A

Virus A ss/ds DNA replicated through DNA/RNA hybrid- partially double-stranded DNA viruses that replicate in the nucleus and cytoplasm of infected cells. dsDNA is completed and transcribed in the nucleus

38
Q

What can DNA from replicative class 7 generate

A

ssRNA+(cellular RNA pol II action)

39
Q

What can happen to genomic RNA in addition to being translated in replicative class 7

A

Genomic RNAs can be reverse transcribed to RNA/DNA and then ss/ds DNS which will be packed in virion

40
Q

What activity does polymerase have in replicative class 7

A

DNA, pol-RNA and -DNA dependent(reverse transcriptase) activity

41
Q

What are some examples of replicative class 7 virus

A

Hepatitis B

42
Q

What’s ‘‘formula’’ to replicative class 7

A

dsDNA–>ssRNA–>mRNA

43
Q

Is DNA transient or labile

44
Q

Do DNA viruses establish persistent infections

45
Q

With what viral DNA genomes have to interact with

A

Host transcriptional machinery( except for poxviruses)

46
Q

Is viral gene transcription temporally regulated in DNA viruses

A

Yes. Early gene encodes DNA-binding proteins and enzymes. Late genes encode structural and other proteins

47
Q

What do DNA polymerases require to replicate a viral genome

48
Q

Is RNA labile and transient

49
Q

Can cell replicate RNA

A

No. RNA viruses must encode RNA-dependent RNA polymerase

50
Q

What does the genome structure of RNA virus determines

A

Mechanism of transcription and replication

51
Q

Are RNA viruses prone to mutation

52
Q

What determines how viral mRNA is generated and proteins processed

A

Genome structure and polarity

53
Q

What viruses must carry polymerases

A

All RNA viruses except for (+) RNA genome

54
Q

What viruses are always enveloped

55
Q

What is reovirus

A

(+/-) segmented RNA genome is template for mRNA(+RNA).(+)RNA may also be encapsidated to generate (+/-) RNA and then more mRNA

56
Q

What happens in retroviruses

A

(+)retrovirus RNA genome is converted into DNA which is integrated into the host chromatin and transcribed as a cellular gene

Microbiology (20 decks)

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