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Microbiology > Viruses: Bacteriophages > Flashcards

Viruses: Bacteriophages Flashcards

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Biology 101 flashcards
1
Q

Basic description of viruses

A
  1. Obligate Intracellular parasites
  2. Infectious agents, but not alive
  3. Inert outside of host cell: only because it is not growing
  4. Once inside host cell: viral genome hijacks host cell’s replication machinery, directs activities of cell
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2
Q

T/F If a dead virus is returned to a host body it will begin to grow again

A

False, nothing will happen, but if an inert virus finds another host it will continue to grow

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3
Q

What is the range of size for a virus and how is it compared to other microbes

A

The smallest of all microbes. Range from the smallest being ~10nm with 10 genes to the largest being ~500 nm

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4
Q

T/F you can observe a virus using a regular light microscope

A

False: can only view an electron microscope

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5
Q

What is a virion

A

A single viral particle

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6
Q

What does a virion contain

A

A nucleocapsid

Genetic information + a protective coat (capsid made up of proteins)

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7
Q

What kind of genetic information is found in a virion

A

DNA or RNA, never both

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8
Q

Naked Virus

A
  • Nucleocapsid
  • Lacks an envelope
  • Not easily destroyed, more resistant to disinfectants
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9
Q

Enveloped Viruses

A

-Nucleocapsid + Envelope
Envelope= a lipid layer
-easily destroyed by disinfectants because the alcohol will interfere with the lipid layer more than the protein coat in naked viruses

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10
Q

Spikes

A

Allow the virus to attach to the specific host cells, essential to enter the host
considered glycoproteins, not always present
animal viruses=spikes
tail fibers=phage

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11
Q

Attachment of naked vs. enveloped virus

A

an envelope virus will always use spikes or envelope to attach
naked virus will use its capsid

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12
Q

Viral nucleic acid/genome (3 points)

A
  • either DNA OR RNA (never both)
  • Linear/circular/fragmented - fragmented is specific to viruses
  • Double or single-stranded- DNA is not always double stranded and RNA is not always single stranded
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13
Q

Capsid

A

-A protein coat: composed of identical subunits called capsomers

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14
Q

How does the virus get its shape

A

By the arrangement of the capsomere subunits

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15
Q

Do viruses contain enzymes, ribosomes or have the ability to generate ATP?

A

NO- they don’t have ribosomes of their own, some completely lack enzymes while some have a few, and don’t have any mechanism for energy production

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16
Q

What is the range of hosts that viruses can affect? How do they choose what host to bind to?

A

There is a great range , they look for specific receptors on the surface of the cell that allows for the binding of the virus

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17
Q

Host specificity

A

viruses will exploit certain receptor molecules that are already present excessively within our cells, which is why specific infections happen in different parts of our body

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18
Q

T/F Viruses are easier to kill once they are intracellular

A

False, you need to catch a virus before it attaches to the host cell because they are very difficult to kill once they are intracellular

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19
Q

What are the three shapes of viruses and what is important about each

A

Icosahedral- specific number of sides
Helical- looks like a tunnel
Complex- contains a phage, uses tail fibers for attachment (spikes)

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20
Q

Naming viruses: family

A

end in suffix- viridae

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21
Q

Naming viruses: genus

A

ends in -virus

Ex: retovirus, Enterovirus

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22
Q

Naming viruses: species

A

name is often the name of the disease
ex: poliovirus, influenza virus

viruses are commonly referred to only by their species names

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23
Q

Bacteriophages: Productive Infections

A
  • Virus goes into the host and actively multiplies

- Increases the number of virulent prodigy

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24
Q

Bacteriophages: Latent Infection

A
  • Virus goes into the cell and remains dormant
  • As a human cell multiplies, a latent cell will multiply its DNA or RNA but will NOT create more prodigies
  • Can remain dormant as long as our immune system can surpass them
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25
Q

T/F Most viral infections are active

A

TRUE

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26
Q

What is a bacteriophage

A

A virus that only infects bacteria

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27
Q

What is the fate of the infected host if there is a productive infection

A

A: Release of virions, host cell lyses and dies
B: Release of virions, host cell does not die and continues to multiply with continuous release of virions

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28
Q

What are the three general types of bacteriophage life cycles based on their relationship with host

A
  1. Lytic phage (virulent)- Productive infection ending with lysis
  2. Temperate phages- (Latent/Lysogenic)- latent infection
  3. Filamentous phages (Extrusion)- productive, but host cell survives
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29
Q

Lytic Phage Infection- Basics

A
  • Lytic/virulent phage exits the host
  • Host cell is lysed
  • It is considered productive infetion since new phage particles are formed
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30
Q

What phage is the model for lytic phage infections

A

T4 phage (dsDNA)

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31
Q

What is the 5 step process of the lytic phage lifecycle

A
  1. Attachment
  2. Genome entry
  3. Synthesis
  4. Assembly
  5. Release
32
Q

Genome entry (3)

A
  1. Only the nucleic acid is injected into the cell, the rest of the phage is outside of the cell where it gets disintegrated
  2. T4 Phage carries enzyme; lysozyme which degrades a little bit of cell wall and allows the nucleic acids to enter
  3. Tail contracts and injects genome through cell wall and membrane
33
Q

Attachment

A
  • Phage exploits bacterial receptors on cell wall

- tail fibers are used

34
Q

T/F phages can only attach to the cell wall of bacteria

A

False, some attach to the flagella or the pilli

35
Q

Synthesis of protein and genome (step 3)

A
  1. Early proteins and late proteins are synthesized
36
Q

What is the role of an early protein during the synthesis phase?

A

Translated within minutes

  • They hijack the host & they take control of the host cell and manipulate it
  • Proteins modifies host’s RNA polymerase (so that it does not recognize its own promoters and will now recognize the phage promoters)
37
Q

What is the role of a late protein during the synthesis phase?

A

produced towards the end of the cycle, are the structural components to make the structure of the new phage (capsid and tail)

38
Q

In what step does this occur? The phage genome is transcribed and phage proteins are produced, and the phage DNA is replicated while other virion components are made and the host DNA is degraded

A

Synthesis phase

39
Q

T/F In the assembly phase, protein modifies the host RNA polymerase so that it will now recognize the phage promoters and not the host promoters

A

False, this occurs in the synthesis phase

40
Q

Assembly (step 4)

A

also called Maturation

  • phage components are assembled to form mature viruses
  • some proteins randomly assemble, others require protein scaffolds
41
Q

What are protein scaffolds

A

components of the new phage that assemble together through protein-protein interactions

42
Q

Release (step 5)

A
  • Lysozyme produced in late infection digests the cell wall

- cell will LYSE, releasing phage

43
Q

What is burst size and what is typical for a T4 phage

A

T4 ~200

-it is the number of phage particles that are released from each infected host

44
Q

Life cycle #2: Temperate Phages

Basics

A

Have the option of following two patterns: Lytic or Lysogenic Infection

45
Q

What is the phage model for the temperate phage

A

Phage Lambda

46
Q

What is the basic definition of a lysogenic infection

A

The virus remains latent in the host cell by incorporating phage DNA into the hosts DNA

(lysogenic always means temperate)

47
Q

What are the steps of a lysogenic pathway (7 steps)

A
  1. attaches to the bacterium
  2. Injected linear phage DNA circularizes and enters lytic or lysogenic cycle
  3. Prophage is integrated into the bacterial chromosome
  4. Phage remains latent in the prophage stage
  5. Cell divides
  6. Prophage DNA is excised and carries an independent lifecycle (becoming active)
  7. Phage DNA enters lytic cycle at the synthesis step
48
Q

What does the term prophage mean

A

Incorporation of phage DNA into host cell genome (lysogeny)

49
Q

T/F an infected cell carrying a prophage is called a lysogen

A

True

50
Q

Once the phage DNA comes out of the dormant stage, it is still considered a prophage

A

FALSE, once it is excised and becomes active it is no longer considered a prophage

51
Q

Until what step is the prophage dormant in the temperate phage life cycle

A

Until after it is excised and no long a part of the bacterial chromosome

52
Q

How does the lambda phage integrate the phage DNA into the bacterial chromosome

A

Through site specific recombination (remains latent)

53
Q

How does the replication of phage DNA occur in the host genome

A
  • Replicates with host chromosome

- The host cell is able to multiply unaffected by the harbored phage

54
Q

What maintains the latent lysogenic state

A

A repressor protein that keeps the phage DNA in the latent stage and in the prophage form

55
Q

How is the phage excised

A

by phage-encoded enzyme

56
Q

What is the trigger for the phage to come out of latency

A

Damage to the host cell DNA will cause the cell to return to lytic infection

57
Q

T/F DNA excised from chromosome only about once per 1,000 divisions of lysogen

A

False, 10,000

58
Q

Why is the prophage DNA excised if DNA is damaged?

A

the repair system will turn on and activate a protease that will in turn destroy the repressor that is keeping the prophage latent

59
Q

What does the term phage induction mean?

A

Causing the phage to become active again by allowing the phage to escape a damaged host

60
Q

What is the difference between the lytic and lysogenic cycle in terms of host DNA

A

lytic: host DNA is degraded
lysogenic: Host DNA is saved and prophage DNA is incorporated within it.

61
Q

What are two advantages of Temperate Phage Infections

A
  1. Partial Immunity

2. Lysogenic Conversion

62
Q

Describe Partial Immunity

A
  • Lysogen is immune to superinfection

- Infected bacterial cell becomes immune, has a higher chance of survival

63
Q

What is superinfection

A

Infection by the same phage

64
Q

Describe Lysogenic Conversion

A
  • bacteria that harbor a phage actually gain new properties
  • Change in phenotype of lysogen from prophage
  • Ex; Aquire the ability to produce toxins
  • Carry the ability to transfer DNA
65
Q

Explain the importance of toxin production by viruses in lysogenic conversion

A

Bacterial phages carry the genes that are responsible for toxin production, will donate this DNA to bacteria then if these bacteria infect humans it will cause the disease

66
Q

T/F Toxins can be produced even when bacteria are not infected by a phage

A

False, Bacteria only produce toxins when they are infected by a phage

67
Q

Match with Medical Importance

  • Corynebacterium diphthariae
  • Clostridium botulinum
  • Escherichia coli O157:H7
  • Stretococcus pyogenes
  • Salmonella enterica
  • Vibrio cholerae
A
  • Causes diphtheria
  • Causes botulism
  • Causes hemolytic uremic syndrome
  • Causes Scarlet fever
  • Causes Food poisoning
  • Causes cholera
68
Q

Life Cycle 3: Filamentous Phage

Basic

A
  • ss-DNA phages that look like long filament
  • Productive infection
  • Host cells not killed by lysis, but grow more slowly
  • Released through extrusion
69
Q

What type of infection does the filamentous phage cause

A

Productive infection- multiplies b large numbers and increases its prodigy

70
Q

What is the model phage for the Filamentous Phage

A

M13

71
Q

How do filamentous phages attach?

A

On the F pili of E. Coli

72
Q

T/F All bacteria can be infected through the filamentous phage

A

False, only bacteria that have a pili

73
Q

What type of DNA is used in the filamentous phage

A

single stranded phage DNA, enters through a hollow tube

74
Q

What is the phage replication method used

A

DNA polymerase of the host synthesizes complementary DNA strand for M13
One DNA strand used as a template for synthesis of mRNA
Another new strand used for copies of the genome

75
Q

What occurs with the protein molecules from the original M13 (2 points)

A
  • When phage DNA replicates, phage capsomeres are synthesized and embedded into the host cell membrane
  • others form pores
76
Q

Describe the Release mechanism of the filamentous phage

A
  • Phage DNA is excreted through pores, coat proteins coat the DNA and form nucleocapsids
  • Phage DNA attaches to the proteins that are incorporated into the membrane, which pushes against the membrane and is released through pores
  • Mature phage DNA leaves surrounded by capsid proteins
77
Q

True/False Bacteria cells lyse when filamentous phages are released

A

False, they exit through pores

Microbiology (7 decks)

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