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Microbiology > Viruses Part B > Flashcards

Viruses Part B Flashcards

Exam 2

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Biology 101 flashcards
1
Q

Are viruses considered cells?

A

No, they are acellular, so they are not cells (prokaryotic cell structure does not apply)

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2
Q

Do all viruses have DNA?

A

No, all cells have DNA and RNA, but viruses have either DNA or RNA

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3
Q

Is an enveloped virus that loses its envelope no longer infectious?

A

Yes because it needs to be in its fully assembled structure to be an infectious virus, which includes its envelope. The first step of replication involves the process of adsorption, the attachment to the host cell with the proteins present on the envelope. Without the parts needed on the envelope to attach, it is no longer infectious

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4
Q

What is the name for a virus that infects bacteria?

A

Bacteriophage

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5
Q

What is the name for a virus that is completely assembled (and therefore, infectious?)

A

A virion

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6
Q

What step-in the process of viral replication would be most directly interfered with if a virus lost its envelope?

A

Adsorption

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7
Q

What is an example of a virulent dsDNA phage?

A

Bacteriophage T4

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8
Q

What does it mean for a virus to be virulent?

A

It means that once the virus is within the host cell, they make many copies of itself which results in the death of the host cell (replicates and lyses the host cell)

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9
Q

Explain the specifics of Bacteriophage T4 replication in regards to the basic steps of viral replication

A
  1. Adsorption
    - The spikes from the virus bonds to the pili on the surface of the E. coli
  2. Entry/Penetration
    - The virus drills a hole through the wall of the host cell to inject its DNA
  3. Synthesis
    - Early mRNA is made which encode early proteins using host RNA polymerase
    - Host DNA is degraded using the viral nucleases in order to stop metabolic reactions
    - Phage DNA genome is replicated using host DNA polymerase
    - Late mRNA is made which includes structural proteins (capsid head, tail fibers)
    - The head and tails are synthesized
  4. Assembly
    - Heads are filled
    - Virions are formed
  5. Release
    - Host cell lysis
    - Many copies of the virus burst out of the cell
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10
Q

What is the Baltimore System based on?

A
  • Viral genome (DNA or RNA? ds or ss? + or -?)

- Steps involved in making mRNA

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11
Q

What is ICTV based on?

A
  • Phylogeny and morphological features

- Compliments the Baltimore system

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12
Q

What is the replication process of dsDNA viruses? (Ex: T4 phage)

A
  1. &2. Adsorption & Penetration
    • Virus lands on host cell
    • Virus attaches to host cell
    • Tail contraction
    • Penetration and unplugging
    • DNA injection
  2. Synthesis: dsDNA can be used to undergo either replication or transcription, then translation to make a protein, then integration of the protein into the virus:
    - Replication
    • Requires the host DNA dependent DNA polymerase to replicate
    • Would then lead to transcription
      - Transcription
    • Requires the host DNA dependent RNA polymerase to transcribe
      - Translation
    • Occurs in the cytoplasm of the host cell and proteins are synthesized by host ribosomes
  3. Assembly
    • All proteins created combine to make a virulent phage
  4. Release
    • Virulent phages burst out of the host cell and the host cell lyses
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13
Q

What is the difference between an early and late protein

A

An early protein is a protein that is made prior to copying the genome. A late protein is a protein that is made after copying the genome.

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14
Q

What is the replication process of +ssDNA viruses? (Ex: oX174)

A

Single stranded genome means you MUST have a replicative form

  1. & 2. Adsorption/Penetration
  2. Synthesis: +ssDNA must make a replicative form of DNA
    - Transcription
    • Uses host DNA polymerase to make -ssDNA and + ssDNA
    • Rolling circle replication to make +ssDNA and +mRNA
      - Translation
    • Occurs in the cytoplasm of host cell and proteins are synthesized by host ribosomes
  3. Assembly
    • Proteins are combined to make a virulent phage
  4. Release
    • New virions exit the host cell
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15
Q

What is the two cycles a temperate dsDNA phage could enter? (Ex: Phage Lambda)

A
  • Lytic cycle
    • Phage injects its DNA into the cytoplasm
    • Phage DNA directs the synthesis of many new phages
    • Cell lyses and releases the new phages
    • New phages can bing to new bacterial cells
  • Lysogenic cycle
    • Phage DNA integrates into host chromosome (Prophage is not actively replicating, but virus is present)
    • Phophage DNA is copied when cell divides
    • Exposure to stress such as UV light triggers excision from host chromosome (stress usually launches it into the lytic cycle)
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16
Q

How does environmental conditions determine the outcome of an infection by a temperate phage?

A
  • Optimal conditions for bacterial cell: lytic cycle
    • Good conditions means it is likely to infect another host cell
  • Poor conditions for bacterial cell: lysogeny cycle
    • Poor conditions means that if it went out of the cell, there may not be another cell to infect
17
Q

What proteins and enzymes are used to respond to the environmental conditions?

A
  • To initiate lysogenic cycle:
    • When bad conditions are sensed, the lambda repressor gene is activated to produce its protein that blocks transcription of genes involved in viral replication
  • To initiate lytic cycle:
    • When good conditions are sensed, the host makes proteases that degrade viral proteins that are needed for the lambda repressor protein, so the transcription of viral replication gens are no longer inhibited
18
Q

What viral protein does the temperate phage lambda gene cI create and what is its function?

A

Protein created: lambda repressor

Function: Increased transcription of cI and decreased transcription of lytic cycle genes

19
Q

What viral protein does the temperate phage lambda gene cII create and what is its function?

A

Protein created: cII

Function: Increased transcription of int and cI

20
Q

What viral protein does the temperate phage lambda gene cIII create and what is its function?

A

Protein created: cIII protein

Function: protects cII

21
Q

What viral protein does the temperate phage lambda gene cro create and what is its function?

A

Protein created: cro protein

Function: Increased transcription of cro & Q, decreased transcription of cI & cII

22
Q

What viral protein does the temperate phage lambda gene int create and what is its function?

A

Protein created: integrase

Function: Endonuclease, which mediates integration of lambda genome into E. coli chromosome

23
Q

What viral protein does the temperate phage lambda gene Q create and what is its function?

A

Protein created: Q protein

Function: Increased transcription of lytic cycle genes

24
Q

What viral protein does the temperate phage lambda gene xis create and what is its function?

A

Protein created: excisionase

Function: Binds integrase and reverses integration

25
Q

What are promoters?

A

Site where RNA polymerase binds to the DNA to initiate transcription

26
Q

What are operators?

A

Gene sequence that allows the proteins responsible for transcription to access the gene sequence

27
Q

What are operons?

A

Cluster of genes that share the same promoter and are transcribed as mRNA (whole section)

28
Q

What does the inhibitor bind to?

A

The operator, restricting the binding of the RNA polymerase

29
Q

What is lysogenic conversion?

A

When a temperate phage induces a phenotypic change in the host cell, which can help for their survival

30
Q

Lytic cycle (summary)

A
  • Bacterial proteases present
  • Favorable environment conditions
  • Proteases degrade cII protein
    • Little/no lambda repressor –> transcribe lytic genes
31
Q

Lysogenic cycle (summary)

A
  • Bacterial proteases absent
  • Poor environmental conditions
  • cII protein present to enhance int transcription
    • cI influenced which creates lambda repressor –> inhibit transcription of lytic genes

Microbiology (9 decks)

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