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BM211: Introduction to Microbiology > Block D Lecture 2: Viruses of Archaea and Bacteria > Flashcards

Block D Lecture 2: Viruses of Archaea and Bacteria Flashcards

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Biology 101 flashcards
1
Q

What does the latent period of a virus life cycle encompass?

A

The eclipse and maturation periods
(Slide 7)

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2
Q

When does the eclipse period start?

A

As soon as the virus enters the host cell
(Slide 7)

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3
Q

What does “burst size” refer to?

A

The number of virions released from an infected host cell
(Slide 7)

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4
Q

What is a bacteriophage (sometimes known as a phage)?

A

A type of virus which infects (and replicates) within bacteria
(Slide 9)

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5
Q

What genomes do most bacteriophages use?

A

dsDNA genomes
(Slide 9)

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6
Q

What components do bacteriophages contain?

A

Heads
Tails
Other components
(Slide 9)

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7
Q

What do viruses which infect archaea resemble?

A

Those which infect enteric bacteria
(Slide 12)

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8
Q

What type of viruses are the only type which have been identified to infect archaea?

A

dsDNA viruses
(Slide 12)

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9
Q

What is the oldest known predator-prey interaction?

A

Bacteria and bacteriophages
(Slide 14)

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10
Q

Why is attachment of a virion to a host cell highly specific?

A

As it requires complementary receptors on the surface of the host and virus cells
(Slide 15)

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11
Q

What does the attachment of a virus to its host cell result in?

A

Changes in both the virus and the host cell’s cell surface that facilitate penetration
(Slide 16)

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12
Q

What bacteria does the bacteriophage T4 infect?

A

E.coli
(Slide 16)

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13
Q

How does the T4 bacteriophage attach to E.coli?

A

Via its tail fibres which interact with polysaccharides on the E.coli cell envelope
(Slide 16)

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14
Q

What happens after T4 bacteriophage tail fibres attach to polysaccharides on the E.coli cell surface?

A

The tail fibres retract, and the tail core makes contact with the E.coli cell wall
(Slide 16)

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15
Q

What happens after the T4 bacteriophage tail core makes contact with the E.coli cell wall?

A

A Lysozyme-like enzyme forms a small pore in the peptidoglycan layer
(Slide 16)

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16
Q

What happens after the bacteriophage T4 uses a lysozyme-like enzyme to form a pore in the peptidoglycan layer?

A

The tail sheath contracts, and viral DNA passes into the cytoplasm by travelling down the central tail tube
(Slide 16)

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17
Q

What 2 features does the doubled stranded DNA genome of the T4 bacteriophage have?

A

It is circularly permuted and terminally redundant
(Slide 17)

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18
Q

What does the T4 bacteriophage having a dsDNA genome that is circularly permuted and terminally redundant affect?

A

Genome packaging
(Slide 17)

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19
Q

What does circularly permuted mean?

A

Circular permutation involves breaking and re-joining the circular molecule at different positions along its backbone, resulting in a new circular molecule with a different starting point for the sequence
(Slide 17)

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20
Q

What does terminally redundant mean?

A

That it contains identical or nearly identical sequences at both ends of the genome
(Slide 17)

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21
Q

Many eukaryotes can utilise RNA interference to diminish virial infections. What is RNA interference?

A

It is a natural cellular process that regulates gene expression by degrading or inhibiting the translation of specific messenger RNA (mRNA) molecules
(Slide 17)

22
Q

What are 3 examples of mechanisms which prokaryotes can use to combat virial infections?

A

CRISPR (similar to RNA interference)
Restriction modification system
Restriction enzymes
(Slide 17)

23
Q

What is the restriction modification system?

A

A DNA destruction system which is only effective against dsDNA viruses
(Slide 17)

24
Q

How can bacteria prevent restriction enzymes they use as defence against bacteria from damaging their own DNA?

A

By modifying their own DNA at restriction enzyme recognition sites
(Slide 17)

25
Q

What are 3 virial mechanisms that T4 ( and other viruses) can use to evade bacterial restriction systems?

A

Chemical modification of virial DNA (via glycosylation or methylation)

Production of proteins which inhibit host cell restriction system

T4 specifically contains a modified base, called 5-hydroxymethylcytosine which is resistant to almost all known restriction enzymes
(Slide 18)

26
Q

What 3 things do T4 bacteriophage early proteins code for?

A

Enzyme for the synthesis and glucosylation of the T4 base 5-hydroxymethylcytosine
Enzymes that function in T4 replisome
Proteins which modify host RNA polyremase
(Slide 20)

27
Q

What does a replisome refer to?

A

The molecular machinery responsible for DNA replication
(Slide 20)

28
Q

What are T4 middle proteins?

A

Additional proteins which modify host RNA polymerase

(Slide 20)

29
Q

What do T4 late proteins code for?

A

Proteins of the virus coat
Structural components
(Slide 21)

30
Q

How is the T4 genome packaged?

A

Precursor of head is assembled
Packaging motor is assembled
dsDNA is pumped into head under pressure using ATP
(Slide 21)

31
Q

What occurs after the dsDNA of the T4 genome is pumped into the head?

A

The T4 tail, tail fibres and other components are added
(Slide 21)

32
Q

What 2 modes can a virus life cycle be?

A

Virulent and temperate modes
(Slide 22)

33
Q

What is the virulent mode?

A

Viruses lyse host cells after infection
(Slide 22)

34
Q

What is the temperate mode?

A

Viruses replicate their genomes in tandem with the host genome and do so without killing the host cell
(Slide 22)

35
Q

What relationship can temperate viruses form with the host cell?

A

A stable genetic relationship
(Slide 22)

36
Q

What is lysogeny?

A

A state where most virus genes are not expressed and the virial genome (known as a prophage) is replicated with the host chromosome
(Slide 22)

37
Q

What is a lysogen?

A

A bacterium containing a prophage
(Slide 22)

38
Q

What may lysogenic viruses do?

A

They may revert back to the lytic pathway and begin producing virions under certain conditions
(Slide 22)

39
Q

What kind of genome does the bacteriophage lambda have?

A

A linear, dsDNA genome
(Slide 23)

40
Q

How can the bacteriophage lambda genome from a double-stranded circle?

A

It contains single-stranded regions at the 5’ terminus of each strand and upon penetration of a cell, these DNA ends base-pair, which forms the cos site, and then the DNA ligates and forms a double-stranded circle
(Slide 23)

41
Q

What can bacteriophage lambda do when it is lysogenic?

A

Integrate its gene into E.coli chromosome at the lambda attachment site
(Slide 23)

42
Q

What does bacteriophage lambda do once it enters the lytic pathway?

A

It synthesises long, linear concatemers of DNA using rolling circle replication
(Slide 25)

43
Q

What is a concatemer?

A

A long DNA molecule that consists of multiple copies of the same DNA sequence linked end to end
(Slide 25)

44
Q

How are lysogenic and lytic events regulated in bacteriophage lambda?

A

By a complex genetic switch containing 2 repressor proteins called the cl protein and the Cro repressor
(Slide 26)

45
Q

What does the cl protein do?

A

It is also known as the lambda repressor and causes repression of lambda lytic events resulting in the activation of lysogeny
(Slide 26)

46
Q

What does the cro repressor do?

A

It controls activation of lytic events by repressing lysogenic genes
(Slide 26)

47
Q

What is key to the balance of cl protein and cro repressor in the cell of the bacteriophage lambda?

A

The physiology of the bacterial host
(Slide 26)

48
Q

What is transduction?

A

The transfer of DNA from one cell to another due to host cell DNA being mispackaged into a phage, which then “infects”another cell with the previous host cell’s DNA
(Slide 27)

49
Q

What does transduction drive?

A

Bacterial evolution
(Slide 27)

50
Q

What are the 2 modes of transduction?

A

Generalised and Specialised transduction
(Slide 27)

51
Q

What is the difference between generalised and specialised transduction?

A

Generalised transduction is when DNA from any portion of the host genome is packed inside the virion

Specialised transduction is when DNA from a specific region of the host chromosome is integrated directly into the virus genome
(Slide 27)

BM211: Introduction to Microbiology (21 decks)

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