(6-13) Viruses of Bacteria-- Bacteriophages Flashcards
1. Describe the composition of a virus. 2. Define: Virus, Virion, Capsid, Nucleocapsid, Capsomere, Spikes or attachment proteins 3. Explain why the structure of the viral genome is unusual. 4. Explain why viruses can multiply only inside cells. 5. Define: Productive infection, Lytic phage, Temperate phage, Latent infection, Lysogenic state 6. Describe the following steps in DNA phage replication: Attachment, Penetration, Transcription, Replication, Assembly or maturation, Release 7. Descri
Viruses can infect organisms of which domain?
Viruses can infect all 3 domains.
A virus particle is called a _______.
Virion
A virion consists of what 2 parts?
Nucleic acid surrounded by protein coat
A viral protein coat is called what?
Capsid
What is a capsid composed of?
Capsomers
What are the 3 virusal shapes?
- Isometric
- Helical
- Complex
Describe the viral genome, including its nucleic acid, shape, and strand characteristics.
- Contains either DNA or RNA
- Can be linear or circular
- Single stranded or double-stranded
Why can viruses only multiply inside metabolizing cell?
Viruses use host machinery to support their reproduction.
Every virus contains information to perform which 3 tasks?
- make viral proteins
- assure replication
- move in/ out of host cells
What 2 phases do viruses live in and what is their metabolic state in each phase?
- Extracellular phase (Metabolically inert)
2. Intracellular phase (“Metabolically” active)
What are the six stages of the Lytic Cycle?
- Adsorption
- Penetration
- Transcription
- Replication
- Assembly (or maturation)
- Release
What occurs during the Adsorption stage of the Lytic Cycle?
- The phage collide by chance with E. coli
~ Remember viruses are metabolically inactive - Protein fibers on phage attach to specific receptors on E. coli
~ Receptors perform other function on cell, but phage co-ops for own purpose
~ T4 attaches to a permease in the outer membrane of E. coli
What occurs during the Penetration stage of the Lytic Cycle?
- Lysozyme located at tip of phage tail degrades E. coli cell wall
- Tail contracts and double stranded DNA is injected through phage tail into cell
- Protein coat remains outside
What occurs during the Transcription and Replication stages of the Lytic Cycle?
- Phage DNA transcribed into mRNA and translated into proteins
- Phage takes over metabolism of cell
- Not all phage proteins synthesized simultaneously
Describe the synthesis of early viral proteins during the Lytic Cycle.
Early viral proteins are synthesized first and are associated with the replication of viral nucleic acid
Ex. a nuclease that degrades E. coli DNA
Describe the synthesis of late viral proteins during the Lytic Cycle.
Late viral proteins are synthesized and are associated with the replication of other viral structures
Ex. capsid proteins, lysozyme to lyse bacteria
Describe the concept of self-assembly, with respect to the Lytic Cycle.
The protein components come together spontaneous due to the specific shape of the caspomers.
The Assembly Stage of the Lytic Cycle is also called _________.
Maturation
What occurs during the Assembly stage of the Lytic Cycle?
- Phage head is formed
- DNA is packed in head
- Tail is attached
- Tail fibers attached
What occurs during the Release stage of the Lytic Cycle?
- Lysozyme synthesized
- E. coli bursts and releases phage to environment
[In the case of T4, 200 phage are released in about 30 minutes]
How do some viruses pick up their envelope as they leave the host cell?
The envelope is made of a portion of the host cell plasma membrane which becomes the lipid envelope of the virus.
Describe 2 ways the Λ (Lambda) Phage may interact with E. coli.
- Λ can go through productive lytic infection (like T4)
2. Λ can be a temperate phage
How can the Λ Phage “Live in harmony” with E. coli?
- During the Lysogenic cycle, the Λ Phage integrates into a specific site in the E. coli genome (between gal and bio genes)
- If E. coli growing slowly (low nutrients) the Λ Phage will integrate.
- If bacteria gets damaged (ex. by UV light), Λ DNA is excised and lytic cycle progresses.
What are the 2 types of transduction that occur with bacteriophages?
- General Transduction
2. Specialized Transduction
What is the difference between general and specialized transduction in bacteriophages?
- General
~ Any gene from fragmented bacterial genome can be transferred to new bacteria - Specialized
~ Transfer of only a few specific genes
~ If Λ phage excises imprecisely from bacteria, may carry either gal gene or bio gene
Define the Host Ranges of Phages.
Number of different bacteria that phage can infect termed host range
Why are Host Ranges of Phages usually limited to a single bacterial species for a single phage?
Phage must be able to attach to host receptors.
What are the 2 ways receptors on bacterial surface can be altered?
- Receptor sites can be altered by mutation
2. Lysogenized bacteria can alter cell surface (alteration of receptor site)
How does virus interaction affect a bacterium?
The effect on bacteria cells depends on infecting phage
Which type of productive infection does not lyse the cell, but keeps it alive?
Extrude viruses
~ Ex. M13 virus of E. coli
Which type of productive infection kills the cell by bursting?
Lytic Phages
~ Ex. T4 virus of E. coli
What is a productive infection?
When phage multiply inside cell, producing numerous progeny (more viruses are produced).
When some phage integrate into host genome, it is termed ________, which means, “______”
- temperate
2. controlled
Which type of infection is termed latent because there may be no sign of infection?
Temperate
The bacteria carrying a temperate phage is termed a _______.
Lysogen
The phage that is integrated within a Lysogen is termed a __________.
Prophage
~ Ex. Lambda (Λ) virus of E. coli
How does a Lambda virus remain lysogenic (temperate) within an E. coli bacterium?
- Protein sticks to DNA
- Repressor sticks to promotor region & prevents Lambda from being excised.
- If damaged by UV light, repressive no longer works and Lambda virus can be released.
- Released Lambda will then enter lytic cycle.
