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Biology > Genetics of Viruses > Flashcards

Genetics of Viruses Flashcards

1
Q

What type of bacteriophage is the T4 bacteriophage?

A

Lytic Bacteriophage (Goes through the lytic cycle)

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2
Q

What does the T4 Bacteriophage infect?

A

Escherichia Coli bacterium (E. Coli)

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3
Q

Mnemonic for the T4 Lytic Cycle

A 
[APSAR]
Attachment
Penetration
Synthesis
Assembly
Release
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4
Q

Attachment of T4 Bacteriophage

A
  • tail fibres bind complementarily to specific cell surface receptors on the host cell wall
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5
Q

Penetration of T4 Bacteriophage

A
  • phage tail release phage lysozyme that digests peptidoglycan cell wall
  • at the same time, base plate pins attach irreversibly to the outer membrane
  • tail sheath contracts, thrusting hollow core and injecting dsDNA into host
  • phage genome enters with help of pilot protein
  • capsid left outside
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6
Q

Synthesis of T4 Bacteriophage

A
  • once inside, T4 takes over host metabolic machinery ; initiates production of phage structural components, phage enzymes and viral dsDNA
  • viral dsDNA used to synthesise mRNA using host RNA polymerase
  • some highly virulent phages produce early viral proteins that degrade host DNA to supply free dNTPs to synthesise viral dsDNA
  • virus dsDNA escapes degradation due to methylation ; more resistant to host restriction enzymes
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7
Q

Assembly of T4 Bacteriophage

A
  • nucleic acids and protein subunits assembled into new virus particles
  • head, tail and tail fibres assembled independently in a sequential manner
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8
Q

Release of T4 Bacteriophage

A
  • phage-coded lysozyme digests peptidoglycan cell wall

- causes osmolysis in which water enters the cell, causing it to burst, releasing the newly assembled virus particles

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9
Q

What type of bacteriophage is the Lambda bacteriophage?

A

Temperate bacteriophage (goes through both the lytic and lysogenic life cycle)

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10
Q

What does the Lambda Bacteriophage infect?

A

Escherichia Coli bacterium (E. Coli)

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11
Q

Mnemonic for the Lamba Bacteriophage reproductive cycle

A

[AP (I PR SI) S A R]

Attachment
Penetration
Integration
Prophage Replication

[Lytic Cycle]
Spontaneous Induction
Synthesis
Assembly
Release
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12
Q

Attachment of Lambda Bacteriophage

A
  • tail fibre binds to specific, complementary cell surface receptors on host cell wall
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13
Q

Penetration of Lambda Bacteriophage

A
  • phage tail release phage lysozyme that digests peptidoglycan cell wall
  • tail sheath contracts, thrusting hollow core and injecting dsDNA into host
  • phage genome enters with help of pilot protein
  • capsid left outside
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14
Q

Integration of Lamba Bateriophage

A
  • dsDNA circularises, preventing degradation by host exonuclease
  • cicularised dsDNA integrated into specific site on bacterial chromosome by the enzyme integrase, forming prophage
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15
Q

Prophage Replication of Lambda Bacteriophage

A
  • prophage genes code for lambda repressor protein ; ensures that prophage remains silent (bacterial cell can continue to reproduce)
  • prophage is replicated together with the bacterial chromosome in binary fission
  • propagation of virus in prophage form without lysis of host cells
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16
Q

Spontaneous Induction of Lambda Bacteriophage

A
  • when host cell experiences stress or cellular damage, prophage is induced to excise from bacterial chromosome
  • repressor protein is destroyed by activated bacterial enzyme
  • lambda phage enters lytic cycle
17
Q

Replication of Lambda Bacteriophage

A

[Early Replication]
- viral dsDNA replicates and directs host metabolic machinery to use cellular raw materials to synthesise bacteriophage components

[Late Replication]
- production of bacteriophage components and enzymes progresses

18
Q

Assembly of Lambda Bacteriophage

A
  • nucleic acids and protein subunits assembled into new virus particles
  • head, tail and tail fibres assembled independently in a sequential manner
19
Q

Release of Lambda Bacteriophage

A
  • phage-coded lysozyme digests peptidoglycan cell wall

- causes osmolysis in which water enters the cell, causing it to burst, releasing the newly assembled virus particles

20
Q

Advantages of Lysogenic Pathway to the Lambda Bacteriophage

A
  1. 1 lambda phage is able to give rise multiple infected cells
  2. Integration of viral dsDNA into the bacterial chromosome to form prophage allows the virus to propagate in prophage form during binary fission
21
Q

Mnemonic for Influenza reproductive cycle

A 
[APUSAR]
Attachment
Penetration
Uncoating
Synthesis
Assembly
Release
22
Q

Attachment of Influenza Virus

A
  • haemagglutinin attaches to sialic acid receptors on the surface of the epithelial cells of the respiratory tract
23
Q

Penetration of the Influenza Virus

A
  • enters host by receptor-mediated endocytosis

- host cytoplasmic membrane invaginates and pinches off, placing the Influenza virus in an endosome

24
Q

Uncoating of Influenza Virus

A
  • low pH environment in endosome stimulates the viral membrane to fuse with the lipid bilayer of the vesicle membrane, releasing the nucleocapsid
  • nucleocapsid degraded by cellular enzymes, leaving 8-segmented ssRNA (-) genome
  • virus RNA polymerase and genome transported to nucleus of host
25
Q

Synthesis of Influenza Virus

A
  • ssRNA (-) used as template by RDRP to synthesise ssRNA (+) / cRNA (+)
  • cRNA (+) serve as templates for synthesis of more viral ssRNA (-) and as mRNA to synthesise virus proteins
26
Q

Assembly of Influenza Virus

A
  • capsid assembles around each viral genome

- HA and NA through GA and transported to cell surface membrane by golgi vesicles

27
Q

Release of Influenza Virus

A
  • each new virus buds from host cell and acquires new coat from host plasma membrane, leaves cell covered in sialic acid
  • sialic acid needs to be removed by NA so HA on other viruses do not attach and cause clumping

Biology (8 decks)

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