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2. BIOL2044- Medical Microbiology > FN - Bacteriophages > Flashcards

FN - Bacteriophages Flashcards

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Biology 101 flashcards USMLE® Step 1 flashcards
1
Q

Which viruses have spikes on their surface?

A

Bacterial viruses have spikes

  • Different from human viruses
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2
Q

What is a virus? (3)

A
  1. Virus infect all living things
  2. We eat and breathe billions of viruses regularly
  3. We carry viral genomes as part of our own genetic material
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3
Q

What is a bacteriophage? (3)

A
  • Virus of bacteria (and archaea), “bacteria eaters”
  • Depend upon a host (bacteria) for replication
  • Bacteria are outnumbered by a factor of 10 to 1 by phages
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4
Q

What acts to increase bacteriphage diversity?

A

crASSphage was assembled in the gut and is present in 50% of humans

  • Acts to increase diversity of the phage in the body
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5
Q

What differences are found in various bacteriophages? (2)

A
  • Type of nucleic acid
  • Morphology
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6
Q

Which phage type is the most abundant?

A

Tailed phages (dsDNA with a tail)

  • 96% of all phages
  • 3 families - myoviridae, siphoviridae, podoviridae
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7
Q

What are bacteriophages made of? (5)

A

Genomic material (linear dsDNA for tailed phages)

Protein content (structural proteins)

  • A capsid encloses and protects the dsDNA
  • A tail, long contractile, long non-contractile, short
  • Adsorption apparatus (baseplate, tail fibers, tail spikes, tail tip
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8
Q

What is the adsorption apparatus?

A

Proteins responsible for the first contact with the host bacteria – adsorption

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9
Q

How does adsoprtion occur? (3)

A

1) First contact of the phage with a “receptor” on the cell surface
reversible adsorption

  • WEAK

2) Phage “walks” on the cell surface to find an ideal place to adsorb irreversibly

  • STRONG

3) DNA ejection into the cell
(may or may not be aided by proteins that degrade the inner membrane)

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10
Q

What is the implication of diversity caused by adsorption apparatus?

A

Adsorption apparatus of phages typically adsorbs to one or two bacterial receptors

→ Implications on the diversity of bacterial strains/species that can be infected by one phage

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11
Q

What are features of bacteriophages adsorbing to hosts?

A

Between Gram

  • Distinct surface compositions

Within Gram

  • Species and strains diverge in the surface molecules displayed
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12
Q

What 2 features contribute to bacteriophage specificity?

A
  • Usually phages infecting species of Gram+ cannot infect species of Gram-
  • Phages can only infect a limited number of strains
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13
Q

How is the DNA ejected into the cell? (3)

A
  1. Viral contractile tail ejection system
  2. Viral long flexible ejection system
  3. Viral short tail system
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14
Q

What type of replication do Virulent phages use?

A

Virulent phages only undergo lytic replication

  • Hijacking of host machinery for genome replication and protein expression
  • DNA packaging and virion assembly
  • Cell burst and release of phage progeny
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15
Q

How does cell lysis occur? (4)

A

Endolysins / Holins

  1. Lytic proteins accumulation
  2. Inner membrane disruption
  3. Peptidoglycan disruption
  4. Outer membrane fusion with inner membrane
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16
Q

What type of replication do Temperate phages use?

A

Temperate phages undergo lytic and lysogenic replication

  • Genome integration
  • Prophage DNA replication with the cell
17
Q

How do temperate phages make the decision between lytic or lysogenic life cycle? (2)

A

1) Environmental

  • Abundance of bacteria and phage
  • Growth conditions

2) Molecular

  • Phages communicate using small molecules
18
Q

What is involved in the Pseudo-Lysogenic life cycle? (2)

A
  • Phage DNA neither replicates nor integrates
  • Phage DNA is carried by one of the daughter cells
19
Q

Why Pseudolysogeny? (2)

A
  • Increases mutation rates in certain parts of genomes
  • Increase specificity to certain types of host
20
Q

Can temperate phages affect bacteria when integrated? (2)

A

Generalised Transduction

  • The phage can carry any part of DNA
  • Initiated during the lytic cycle of a virulent bacteriophage

Specialised Transduction

  • The phage carries only the specific part of DNA
  • Initiated during the lysogenic cycle of a temperate bacteriophage
21
Q

During phage assembly inside the cell, how is DNA encapsidated? (4)

A

Most dsDNA viruses follow a headfull packaging system

  1. Terminase binds viral genome
  2. Terminase-DNA binds procapsid portal
  3. DNA translocation
  4. Contamer cleavage and packaging completion
22
Q

How do we isolate phages? (5)

A
  1. Add sample to bacteria
  2. Add phage-infected bacteria to molton top agar
  3. Pour immediately onto the agar plate
  4. Rotate to spread evenly, agar solidifies
  5. Incubate overnight

2. BIOL2044- Medical Microbiology (20 decks)

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