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Fundamentals I > Intro to Viruses > Flashcards

Intro to Viruses Flashcards

1
Q

What is the mutation rate for RNA viral replication?

A

Very error prone bc no proof-reading capability: 10^-3 - 10^-4. Adaptability advantage to virus but problematic to antiviral therapy. ~1 mutation per round of replication

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2
Q

What is the genome type for most DNA viruses

A

linear double stranded

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3
Q

Name 3 exceptions to the general genome type for DNA viruses

A

Papovavirus: dsDNA is circular, not linear –> template for both mRNA and genome replication

Parvovirus: ss linear DNA

Circovirus: circular ssDNA

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4
Q

What is notable about the Circovirus

A

Smallest autonomously propagated virus; circular ssDNA

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5
Q

Two main shapes for viral capsids

A

Helical, Icosahedral

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6
Q

Where do enveloped viruses get their lipid membrane

A

Derived from the host cells membrane

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7
Q

How many families of viruses can infect humans

A

21

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8
Q

Describe Icosahedron symmetry

A

Nature’s perfect structure: high physical strength and rigidity –> withstand extremes in pH, temp, solvents and can perist outsidde the body
20 equilateral triangles

Examples: adenovirus, poliovirus, Hep A and E

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9
Q

What is the current classification strategy for viruses

A

Features of viral genome

1) Genome composition (DNA vs RNA)
2) Genome structure and organization
3) Morphology

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10
Q

What is the current virus classification omenclature

A

Family/subfamily/genus/species/strain

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11
Q

Name the 6 stages of the Viral Lifecycle

A

1) Attachment to the surface of the target cell
2) Penetration into the cell
3) Uncoating
4) Replication (including macromolecular synthesis events)
5) Assembly of virion components
6) Release of infectious progeny virus

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12
Q

What is the cellular receptor for HIV-1

A

CD4

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13
Q

What is the cellular receptor for EBV

A

CD21 (Remember the EBV can cause B cell cancers –> CD21 is a B cell marker)

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14
Q

What is the cellular receptor for Rabies

A

ACh receptor (remember that all rabies symptoms are all neural and ACh is a molecule of neural synapses)

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15
Q

What is the cellular receptor for HCV

A

CD81

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16
Q

Name a cellular receptor common to many viruses

A

Sialic Acid

17
Q

What is the most important determinant of viral tropism

A

Cellular receptor type: cells lacking the right receptor are no susceptible to infection

18
Q

What are the 3 mechanisms of viral penetration

A

1) Translocation of entire virion across the plasma membrane
2) Endocytosis of the virus particle resulting in their accumulation inside cytoplasmic vacuoles
3) Fusion of the cellular membrane with virion envelope

19
Q

What step marks the beginning of the eclipse phase? What is significant about this phase

A

Viral uncoating; during this period no infectious virion can be recovered from the cell –> demonstrated in classical one-step growth experiment

20
Q

What viruses replicate in the cytoplasm? Exceptions?

A

RNA viruses and the pox viruses

Exceptions: retroviruses and othomyxoviruses

21
Q

What viruses replicate in the nucleus? Exceptions?

A

DNA viruses (except for pox viruses) and the orthomyxoviruses

22
Q

What enzyme does a dsRNA virus require for replication of the viral genome? What is the product of function?

A

dsRNA polymerase: mRNA

23
Q

What enzyme does a negative strand ssRNA virus require for replication of the viral genome? What is the product of function?

A

ssRNA polymerase: both + and - strand RNA; mRNA

24
Q

What enzyme does a retrovirus require for replication of the viral genome? What is the product of function?

A

RNA-dependent DNA polymerase (reverse transcriptase): dsDNA

25
Q

What enzyme does a DNA virus require for replication of the viral genome? What is the product of function?

A

DNA-dependent DNA polymerase: dsDNA

26
Q

What essential genome product must be made by all viruses?

A

mRNA

27
Q

Name a family of (+) sense RNA viruses with examples.

A

Picornaviruses: poliovirus, Hep A, rhinovirus

+ ssRNA can function directly as an mRNA in infected cell –> genome is first translated in order to provide the enzymes needed for replication (doesn’t carry enzymes with it)

28
Q

Name a family of (-) sense ssRNA viruses with examples.

A

Orthomyxoviruses (influenza) or Paramyxoviruses (parainfluenza and RSV)

Enzymes needed for mRNA production must be carried in mature virus (ssRNA polymerase)

29
Q

Name a family of dsRNA viruses with examples.

A

Reoviruses: rotavirus

Cause significant disease in children

Enzymes for mRNA production must be carried within virion: dsRNA polymerase

30
Q

Name an example of a retrovirus

A

HIV

Must carry reverse transcriptase in the virion

HIV acquires its envelope by budding through the cell membrane

31
Q

Give an example of a dsDNA virus

A

Herpes simplex virus. Can utilize host RNA polymerases to produce viral mRNA and host DNA polymerases to replicate its genome

32
Q

What programs viral subunits (nucleic acid, structural proteins and enzymes) to assemble into a compact, arranged virion?

A

The program for assembly is carried with the PHYSICAL PROPERTIES of each subunit

33
Q

How are naked viruses typically released from the cell?

A

Accumulate in cytoplasm and are released during cell lysis

34
Q

What does “virus morphology” refer to?

A

The nucleocapsid architecture

35
Q

Define “replicase”

A

Complex of viral and/or host proteins required to replicate the viral nucleic acid genome. Include viral polymerases and cofactors

36
Q

Describe a very unique feature of rotavirus.

A

Rotavirus is dsRNA. dsRNA is a danger signal to mammalian cells, so capsid proteins are made early and the capsid is partially assembled to keep dsRNA hidden.

37
Q

What 4 things must retroviruses carry with them in addition to their genome?

A

Reverse transcriptase
primers
integrase
other enzymes

Fundamentals I (4 decks)

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