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Microbial Ecology (BIOL 355) > Lecture 11: Viruses > Flashcards

Lecture 11: Viruses Flashcards

1
Q

What is a virus?

A

A small infectious agent that can only replicate inside the cell of a living organism

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2
Q

What is a phage?

A

A virus that only infects bacteria

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3
Q

What is a virion?

A

A virus on the outside of a cell

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4
Q

What are the 3 components of the viral structure?

A
  1. Nucleic acid core
  2. Capsid
  3. Envelope
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5
Q

Describe the nucleic acid core.

A
  • DNA or RNA
  • Single of double stranded
  • Circular, linear, segmented, or mixed
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6
Q

What is a capsid?

A

Protein coat that encases nucleic acids
- May contain lipids

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7
Q

What is the envelope (viral structure)?

A

Lipid membrane outside the capsid
- Only in some viruses

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8
Q

How are viruses classified?

A
  • By the organisms they infect
  • Also shapes: rods and spheres
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9
Q

Why is a small viral genome advantageous?

A

Faster replication –> an infect other cells faster

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10
Q

One question about the origin of viruses is did they predate cellular life. What evidence supports this idea?

A

Some viral genomes look different from host counterparts

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11
Q

What are generalists vs. specialists?

A
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12
Q

What are the types of viral life cycles?

A
  • Lytic: lyses host cell
  • Lysogenic: viral DNA merges with host DNA
  • Chronic
  • Pseugolysogeny: stalled development of the bacteriophage in the host cell, usually caused by unfavorable conditions for the host cell
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13
Q

What are the 2 stages of the viral life cycle?

A
  • Extracellular: inert viral particle in environment
  • Intracellular: reproduction stage
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14
Q

What are the general steps of the lytic life cycle?

A
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15
Q

What are the general steps of the lysogenic life cycle?

A

DNA is replicated but not translated into proteins

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16
Q

What some defenses bacteria have evolved against viruses (before and after infection)?

A
  1. Before infection
    - Prevent absorption to surface
    - Decoys
    - Prevent phage DNA entry
  2. After infection
    - Cutting phage nucleic acids
    - CRISPR-Cas system
    - Abortive infection
17
Q

The Baltimore classification system classifies viruses based on _____.

A

nucleic acids

18
Q

In which class type in the Baltimore classification system would you expect a higher mutation rates?

A

RNA
- Less mechanisms to correct errors that occur in the replication process

19
Q

True or false: viruses make up the largest abundance and biomass on Earth

A

True (15x more abundant than hosts)

20
Q

Where are viruses mostly found? Where else are they found?

A
  • Mostly in aquatic/marine environments
  • Also in soil/desert sand/sea ice
21
Q

Why are viruses a major driver in the “microbial loop”?

A

Because they are one of the main causes of mortality among prokaryotes in environment microbial ecosystems

22
Q

What effects do viruses have on the ecosystem?

A
23
Q

What effect did the seastar wasting disease have on its ecosystem?

A

Decreased ecosystem diversity
- Mussel population grew out of control
- No room for other organisms like barnacle or algae

24
Q

To which other groups are plant viruses clustering? Why?

A

Fungi and arthropods
- Probably because they are generalists

25
Q

Define trade-offs in ecology.

A

The use of resources for one function (such as reproduction) can reduce the resources available for another function (such as survival)

26
Q

Why is the diversity of this pool of viruses maintained?

A
27
Q

Explain what is happening here.

A

The infection by cyanophages substantially limited the range in which procholorococcus thrives

27
Q

Why are water fowl the primary reservoir for influenza viruses?

A
  • Viruses are shed in feces (easily spread through water)
  • Water fowl are usually migratory
28
Q

What makes viruses so succesful?

A
  1. Growth
    - Faster than eukaryotes and prokaryotes
    - Infection of one cell culd produces thousands of particles per cell
    - Viruses have more options to pass on genetic material
  2. Abundance
    - Outnumber all biological forms
  3. Biodiversity
    - Simple to complex body form

Microbial Ecology (BIOL 355) (17 decks)

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