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Bio 1113 > Bacteriophage basics > Flashcards

Bacteriophage basics Flashcards

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1
Q

How many genes are in the typical phages (dsDNA tailed)

A

50-250 genes

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2
Q

What must be required for a successful plaque assay?

A

Multiple rounds of phage infection and growth

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3
Q

Why do lytic phages generally form clear plaques?

A

They kill the bacteria

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4
Q

What does a phage have to be able to interact with in a host bacteria?

A

The host cellular machinery including the host transcription and translation systems

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5
Q

What happens to the phage genome in the lysogenic cycle?

A

It becomes stably maintained within the cell, even through many subsequent generations of cell division

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6
Q

How do bacteriophages replicate?

A

They require a bacterial host and take advantage of the host’s cellular machinery and redirecting it toward viral reproduction

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7
Q

What are some other less known structures of phages?

A

Single stranded DNA or RNA can can be enveloped with a lipid membrane, have one or than one chromosome, or have a variety of other configurations

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8
Q

Are bacteriophage particular to hosts? If so, how?

A

Yes, the host range can be a single bacteria strain or it can span multiple bacterial species or genera. However, there are few if any phages with a host range that spans different bacterial orders and the possibility of spanning different phyla is even less likely

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9
Q

When the bacterial host cell is lysed and the new virions are released. Part of the lytic cycle

A

Phase 6 - Cell lysis and phage release

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10
Q

How simple can it be for phages to alter their host ranges?

A

Sometimes a single base mutation in their genome is enough to alter their host range

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11
Q

How long does it take G. terrae to form a lawn in lab?

A

2-3 days

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12
Q

When prophage-encoded and expressed proteins alter the host cell surface in such a way that other phages are excluded from adsorption and DNA injection

A

Exclusion

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13
Q

When the phage chromosome circularizes inside the host cell. Part of the lytic cycle

A

Phase 2 - Phage DNA circularization

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14
Q

What is morphology?

A

The color, size, and shape. The characteristics that vary between species

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15
Q

What are virions?

A

Late-gene products that are the structural proteins that comprise the new phage particle. The new phages

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16
Q

What is a common mechanism used by prophages to ensure its stability?

A

Integrating into the host chromosome through a process known as homologous recombination

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17
Q

What is the estimated number of phage population?

A

10^31 particles

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18
Q

What are the main parts of a bacteria?

A

A flagellum, cell wall, cytoplasmic membrane, cytoplasm, capsule, pili, ribosomes, and bacterial DNA

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19
Q

What happens when a prophage is integrated in a lysogen (host cell)?

A

The prophage is replicated by the host DNA polymerases and passed to both daughter cells during normal cell division

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20
Q

What is it called when we provide bacteria a media to grow in without other bacteria?

A

culturing bacteria

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21
Q

What happens to the genes required for the lytic cycle in the lysogenic cycle?

A

They are repressed, rather than expressed

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22
Q

How many bacteria are generally in a colony?

A

generally 10^7-10^8 cells

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23
Q

What are the percentages of a phage entering the lytic and lysogenic cycles?

A

80-90 go to lytic and 10-20 go to lysogenic

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24
Q

What do G. terrae colonies look like?

A

orange, round, rough, and dry in texture

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25
Q

What are bacteriophages?

A

viruses that infect bacterial hosts and have properties shared by all viruses

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26
Q

What has recent evidence suggested is possibly the “normal” phage life cycle?

A

Lysogenic cycle

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27
Q

What is the structure of the majority of the phages?

A

Tailed viruses containing a double stranded DNA genomes (Caudovirales). The linear DNA is contained in a protein shell (head or capsid) which is attached to a tail

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28
Q

What are the best characterized systems for bacterial resistance to phages?

A

Restriction, abortive infection, and CRISPR

29
Q

What are the two phage life cycles?

A

Lytic and lysogenic (temperate)

30
Q

What are late-genes?

A

Following early gene expression, a new set of phage genes are expressed called late genes

31
Q

What do rRNA do for bacteria?

A

construct models of their evolutionary relationships (phylogeny)

32
Q

Who were the major contributors in discovering phages?

A

Frederick Twort and Felix D’Herrelle

33
Q

How is the growth rate of bacteria measured?

A

Doubling time. It is a logarithmic function

34
Q

What method did D’Herrelle develop that is still used today when discovering phages?

A

Plaque assay

35
Q

At what phase of the phage cycle do cells enter the lytic or lysogenic cycle?

A

Phase 2 - Phage DNA circulariziation

36
Q

When were phages first discovered?

A

1915-1917

37
Q

What is the host bacteria used in lab?

A

Gordon terrae 3612

38
Q

What is the most abundant “life form”?

A

Bacteriophage

39
Q

What is the range of doubling time for bacteria?

A

15-20 minutes up to days/weeks

40
Q

How does a lysogen resist infection?

A

constitutive expression of the immunity repressor protein from the prophage, its subsequent binding to the prophage DNA, and the repression of transcription of the lytic genes

41
Q

All bacteria have differing what?

A

ribsomal RNA (rRNA) sequences

42
Q

What are the 6 phases of the lytic cycle?

A
  1. ) Phage adsorption and DNA injection
  2. ) Phage DNA circularization
  3. ) Phage DNA replication
  4. ) Phage heads and tails production and more DNA replication
  5. ) DNA packaging and phage assembly
  6. ) Cell lysis and phage release
43
Q

When a phage attaches and adsorbs to a host cell using its tail fibers and injects its linear chromosome into the bacterium. Part of the lytic cycle

A

Phase 1 - phage adsorption and DNA injection

44
Q

Why do lysogenic phages generally form cloudy plaques?

A

They contain a mixture of dead bacteria and lysogens

45
Q

What is G. terrae grown in in lab?

A

PYCa media at 30 degrees C

46
Q

What is G. terrae?

A

a gram positive soil organism whose relatives are well equipped to break down hydrocarbons

47
Q

What do all bacteria in a colony have in common?

A

They are all identical because they came from the same single cell

48
Q

What is a key factor in determining if a phage can infect a bacterial host?

A

If the host includes a receptor in the cell wall a phage can recognize and adsorb to

49
Q

What happens to some prophages that don’t integrate into the host genome?

A

It is established as a large extrachromosomal plasmid (DNA) that encode and express several partitioning proteins that ensure each daughter cell receives a copy of the prophage plasmid

50
Q

What does CRISPR stand for

A

Clustered regularly-interspaced palindromic repeats

51
Q

When the phage heads and tails are produced. Part of the lytic cycle

A

Phase 4 - Phage head and tail production/more DNA replication

52
Q

What is a bacterial lawn?

A

When many bacterial cells are added to a media and cover the surface in one sheet rather than individual colonies

53
Q

What is the cell that carries a prophage called?

A

Lysogen

54
Q

How do we determine the host range of phages?

A

It must be determined experimentally because they change frequently

55
Q

Can a lysogen carry multiple prophages?

A

Yes, they are integrated at different locations in the chromosome

56
Q

Where did the bacteria come from in this lab?

A

An oil contaminated soil sample in China

57
Q

How many cells are considered to be in a saturated culture?

A

2-4 x 10^9 cells/mL

58
Q

What do all bacteria lack? And roughly how large are they?

A

They lack a nuclear membrane and other membrane-bound organelles. They are usually 1-5 microns across (a red blood cell is 8)

59
Q

What types of plaques do lytic and lysogenic (temperate) phages form?

A

Lytic phages form clear plaques and lysogenic phages form cloudy plaques

60
Q

What are lytic phages also know as?

A

Virulent phages

61
Q

How do bacterial cells divide?

A

Binary fission

62
Q

What is the range of genes phages can have?

A

A handful to more than 500

63
Q

When the phage DNA is replicated. Part of the lytic cycle

A

Phase 3 - Phage DNA replication

64
Q

When new virions are assembled. Part of the lytic cycle

A

Phase 5 - DNA packaging and phage assembly

65
Q

How many genes are typically in a bacterial host?

A

Possibly 6000 or more

66
Q

A single phage particle present within a lawn of bacteria (thin layer) growing in a Petri dish can propagate in the bacteria to form a clearing. It is created by the destruction of bacteria cells by phage

A

Plaque or plaque assay

67
Q

What is the phage genome called within the cell?

A

Prophage

68
Q

What is G. terrae often used for?

A

Bioremediation (breakdown of pollutants) and industrial biotechnology

69
Q

The ability of a lysogen to resist infection from an invading phage by repressing the invaders lytic genes

A

Superinfection immunity

Bio 1113 (22 decks)

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