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Virology > Lecture 3: viral genome and classification > Flashcards

Lecture 3: viral genome and classification Flashcards

1
Q

what do all viral genomes need to make in order to be recognized by host ribosomes

A

mRNA

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2
Q

describe the baltimore classification system

A

designed by david baltimore

all viruses must produce mRNA

source of RNA polymerase from host cell or virus

(+) sense RNA viruses (5’-3’)
-direct translation

(-) sense RNA virus (3’-5’)
-antisense strand, lacks coding regions

large viruses are encodes for by virus

small viruses hijack from host cell or virus

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3
Q

how can (+) sense RNA virus be directly translated

A

5’ cap and 3’ poly A tail tricks cell to allow it in; recognized mRNA by ribosomes

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4
Q

mRNA is always on the ( ) strand

A

+

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5
Q

DNA of equal polarity is on ( ) strand

A

+

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6
Q

RNA and DNA complements of ( ) strands are ( ) strands

A

+

-

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7
Q

ribosome ready and can be translated into protein

A

mRNA

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8
Q

7 viral genome types

A 
dsDNA
gapped dsDNA
ssDNA
dsRNA
ss (+) RNA
ss (-) RNA
ss (+) RNA with DNA
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9
Q

what info is encoded by the viral genome

A

gene products and regulatory signals for:

  • replication of genome
  • assembly/packaging of genome
  • regulation of replication cycle
  • controlling host defenses
  • transmission to other cells and hosts
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10
Q

info not encoded in viral genome

A
  • no complete protein synthesis machinery (elF’s and tRNA)
  • not involved in energy production/ membrane synthesis
  • lack essential centromeres or telomeres found in host chromosome
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11
Q
  • dsDNA
  • cellular (or viral) DNA-dependent RNA polymerase
  • adenovirus, herpesvirus, polyomavirus, poxviruses
A

baltimore class 1

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12
Q
  • ssDNA
  • cellular DNA-dependent RNA polymerase (ssDNA to dsDNA)
  • circoviruses, parvovirus
A

baltimore class 2

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13
Q

describe RNA genomes

A
  • cells lack RNA-dependent RNA polymerase (RdRp) activity capable of replicating viral RNA
  • RNA virus genomes encode an RdRp
  • RdRp produce RNA genomes and mRNA from RNA templates
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14
Q
  • dsRNA
  • virion packaged RdRp
  • mRNA synthesized from (-) sense strand
  • rotavirus, reovirus
A

baltimore class 3

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15
Q
  • ssRNA
  • (+) sense RNA translated
  • picornaviruses, flaviviruses, coronaviruses, togaviruses
A

baltimore class 4

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16
Q

examples of ssRNA (+) sense

A
  • poliovirus, rhinovirus
  • gastroenteritis
  • SARS
  • yellow fever virus, west nile, hep C virus
  • rubella virus, equine encephalitis virus
17
Q
  • ssRNA
  • (-) sense RNA not translated
  • virion packaged RdRp
  • synthesize (+) sense viral mRNA
  • filoviruses, orthomyxoviruses, paramyxovirus, rhabdovirus
A

baltimore class 5

18
Q

examples of ssRNA (-) sense

A
  • measles, mumps
  • rabies
  • ebola, marburg virus
  • influenza
  • lassa virus
19
Q

consequence of segmented genome

A

reassortment

20
Q

coding strategy used by arenaviruses and some members of the bunyavirus family, in which an RNA genome segment contains both positive- and negative- sense genes

Therefore, some viral proteins are made from messenger RNAs copied from the genome RNA, while other proteins are made from messenger RNAs
copied from the antigenome RNA.

A

ambisense RNA genomes

21
Q

-ssRNA
-(+) sense
-virion associated reverse transcriptase (ssRNA to dsDNA)
carries its own reverse transcriptase
-retroviruses (HIV)

A

baltimore class 6

22
Q
  • ssDNA/dsDNA
  • virion associated reverse transcriptase
  • hepdnaviruses (Hep B)
A

baltimore class 7

23
Q

example of gapped dsDNA genome

A

hep B

24
Q

how are viruses classified

A

virion properties
host interactions
molecular properties

25
Q

how are viruses classified through virion properties

A

filterable agents
disease symptoms
physical properties
-biomechanics, virion morphology, and serology

26
Q

how are viruses classified through host interactions

A

transmission (vectors)

entry (envelope fusion, receptors)

27
Q

how are viruses classified through molecular properties

A 
genome (topology- ss or ds; strandedness)
sequence data (genome and capsid protein)
replication mechanisms
28
Q

sequence homology
similar hosts
target cells/ tissue

A

species

29
Q

virion size/shape
replication strategy
genome organization

A

genus

30
Q

virion structure

replication mechanisms

A

family

31
Q

genome composition

genome topology

A

order

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