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I & I Part II > Mechanisms of Viral Replication > Flashcards

Mechanisms of Viral Replication Flashcards

1
Q

6 Discrete Steps of Virus Replication

A
  1. Adsorption to the host cell
  2. Penetration or entry
  3. Uncoating
  4. Synthetic phase: transcription, translation, genome replication
  5. Virus Assembly
  6. Virus Release
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2
Q

Adsorption to the Host Cell

A

•Specific binding of the virions spikes to the host cell receptors

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3
Q

Two Mechanisms of Virus Entry

A
  • Fusion
  • Viropexis
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4
Q

Viral Entry - Fusion

A
  • Some enveloped viruses enter cells by membrane-envelope fusion
  • Viral envelope becomes part of plasma membrane
  • Herpesviruses, Paramyxoviruses
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5
Q

Viral Entry - Viropexis

A
  • Some enveloped viruses and naked capsid viruses are taken in by receptor mediated endocytosis
  • Orthomyxoviruses, Poliovirus
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6
Q

Uncoating

A
  • Removal of viral proteins
  • Results in release of viral genome into cytoplasm or nucleus
  • Uncoating may be complete or partial
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7
Q

Synthetic or Virion Components Production

A
  • Transcription: Synthesis of mRNA
  • Replication: Synthesis of viral genomes
  • Early Functions: Synthesis of early proteins
  • Late Functions: Replication of viral genomes and structural proteins synthesis
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8
Q
A
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9
Q
A
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10
Q

DNA virus replication

A

•Transcription

ss DNA——> ds DNA———> mRNA

•Replication

ds DNA——> ds DNA

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11
Q

+RNA virus replication

A
  • RNA (+) sense viruses replicate in the cytoplasm, using their own newly synthesized RNA dependent RNA polymerase, also called RNA transcriptase (exception -retroviruses: they replicate in the nucleus via DNA intermediates)
  • to synthesize the early proteins (RdRp) needed to make make more +RNA (which leads to more and more proteins being made):

(+) RNA = mRNA —-> proteins

•then, Transcription

(+) RNA——> (-) RNA——> mRNA (+) —> even more proteins

•Replication

RNA——> (-) RNA——> RNA

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12
Q

-RNA virus replication

A
  • RNA (-) sense viruses replicate in the cytoplasm, using their own virion associated RNA dependent RNA polymerase (exception-orthomyxoviruses: they replicate in the nucleus)
  • Transcription

(-) RNA——> (+) = mRNA

•Replication

(-) RNA——> (+) RNA——> (-) RNA

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13
Q
A
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14
Q

DNA Virus Transcription

A
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15
Q

RNA Virus Transcription - 3 Ways

A
  • segmented genome
  • monocistronic mRNAs
  • monocistronic mRNAs translated into a polyprotein and cleaved into mature proteins
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16
Q

Monocistronic mRNA - Segmented RNA

A
17
Q

Monocistronic RNA - Negative Sense RNA Viruses

A
18
Q

Monocistronic mRNA - Positive Sense RNA Viruses

A
19
Q

Virus Assembly - Naked Capsid Viruses

A
  • Capsomeres assembled
  • Capsomeres formed into capsids
  • Nucleic acid added to form complete particles
20
Q

Virus Assembly - Enveloped Viruses

A
  • Membrane acquires viral encoded spikes or peplomers
  • Matrix protein aggregates at membranes
  • Nucleocapsid migrates beneath matrix protein
  • Nucleocapsid enclosed by membrane (budding)
21
Q

Virus Release

A
22
Q

Productive or lytic response:

A

Successful viral replication cycle is called productive or lytic response.

23
Q

Lytic or virulent viruses:

A

Viruses that can lead into productive infection are called lytic or virulent viruses.

24
Q

Non-productive response:

A

The genome of some viruses can persist indefinitely and the host cells survives and divides without any virus production, called non-productive response.

25
Q

Temperate viruses:

A

Viruses that can undergo both productive and non productive responses are called temperate viruses.

26
Q

Bacteriophages

A
  • Viruses of bacteria are called bacteriophages
  • Some of the important bacteriophages are T2, T3, T4, T5, T7, Lambda, Phi-X, M13
  • T4 and Lambda studied in detail
  • Two phases of infection; Lytic (productive infection) and Lysogenic (nonproductive)
  • Productive phage infection leads to inhibition of host cell functions
  • Lysogenic phage can be induced
27
Q

Prophage

A

Phage genome integrated into bacterial chromosome

28
Q

Lysogeny

A

Phage infection leading to formation of prophage

29
Q

Lysogen

A

A bacterium harboring prophage

30
Q

Temperate phage

A

A phage that undergoes lysogeny

31
Q

A phage that undergoes lysogeny

A

Induction of prophage to vegetative stage

32
Q

Vegetative stage

A

Replication of phage genome and production of phage progeny

33
Q

Lysis

A

Disruption of host cell and release of phage progeny

34
Q

Lysogenic conversion

A

Expression of gene functions by the prophage leading to phenotypic property of host bacterium

35
Q

Lambda

A

Temperate (productive and nonproductive); T4: Lytic

36
Q

Plaque Assay

A

I & I Part II (25 decks)

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