bmf Chapter 13

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Viruses of Bacteria

Who coined the term filterable viruses?

Iwanowsky.

Who was responsible for the crystallization of Tobacco Mosaic Virus?

Stanley.

Viruses that infect bacteria are called?

Bacteriophages.

What is a virion?

It is an individual virus particle.

The protein coat of a virus is composed of..

Protein, and either RNA or DNA.

What shapes can a virus be and what determines its shape?

Icosahedral (isometric), helical, or complex. It is determined by its capsid.

The viral envelope closely resembles?

The eukaryotic cell membrane.

Describe spikes and their function.

They are protein projections on the surface of a virus that are involved in attachment to the host cell.

Viruses can live outside or inside cells; what state are they in respectfully?

Outside of living cells, viruses are metabolically inert.

The bacteriophage enters through the host cell wall by?

The nucleic acid.

List the correct order for the stages of a phage infection.

Attachment, penetration, transcription, replication of nucleic acid and protein, assembly, and release.

*A surprisingly relatively recent finding is that, in the ocean..

Bacteria and viruses occur in much larger numbers than originally thought.

*Viruses...

Probably keep the numbers of bacteria in check and are active in passing DNA from one bacterium to another.

*A phage that replicates inside the host cell and then lyses its host during its release is a..

virulent phage.

*Phages that can either replicate and cause cell lyrsis or can integrate their DNA into the host DNA are called

lysogenic phages

*One of the most intensively studied virulent phages which infects E. coli is

T4

*During attachment of phage to E. coli, the phage

Randomly bump into the bacteria and attach to proteins or carbohydrates on the bacterial surface

*What part of the E. coli T4 phage attaches to the host cell receptors?

Protein fibers at the end of the phage tail.

*During penetration of E. coli by the T4 phage..

the tail acts as a "hypodermic needle", injecting the phage DNA into the cell.

*Phage-induced proteins are..

Proteins normally present in the uninfected cell and early proteins.

*Phage-induced enzymes are ..

Produced in a sequential manner and used to customize the cell for viral production.

*Assembly of the T4 phage..

May involve some self-assembly and may involve the use of scaffolds.

*the process of separate replication of viral protein and its nucleic acid is termed..

Vegetative reproduction.

*In the case of T-even phages, the burst size is about..

200 per host cell.

*The time from absorption to release for T-even phage is about..

30 minutes.

An exit method used by viruses which does not immediately destroy the host bacterium is..

budding.

*A positive-sense strand of RNA..

Is the only form of RNA found in phages and acts directly as mRNA.

*In the replication of phage containing positive-sense RNA,..

a phage-encoded RNA polymerase is used to make negative-sense RNA using the phage positive-sense RNA as a template.

RNA phages usually contain..

Positive-sense RNA.

Describe phage replication.

The majority of phages are temperate. When integrated into host DNA, the phage DNA is called a prophage. Lambda is a good example of a temperate phage.

*A temperate phage..

May be lysogenic and chooses between lysogenic and lytic cycles shortly after entering the host cell.

*The integration of phage DNA into the bacterial chromosome occurs because of..

Identical DNA sequences in both.

*Once integrated, phage DNA can remain in the prophage state as long as..

Certain phage genes are repressed.

*The activation of the SOS system in a bacterium infected with a prophage results in..

Complete lysis of the bacterial culture and destruction of the viral repressor through host protease activity.

*Lysogenic cells..

Are immune to infection by the same virus and may have new properties.

*The phenomenon responsible for the ability of Corynebacterium diptherium to produce the virulent toxin responsible for the devastating effects of diptheria is called

Lysogenic conversion.

*Which of the following organisms does not have its virulence increased by lysogenic conversions?

Mycobacterium tuberculosis.

*The bacterial viruses that are released by a process terms extrusion are called..

Filamentous phages.

The filamentous phages all contain..

Single-stranded DNA

*Bacteria infected with filamentous phages are termed..

Carrier cells.

*Transducing virulent phages do not lyse the cells they invade because..

Bacterial DNA has replaced critical viral DNA in the phage.

*The groups of organisms that a virus may infect is known as its..

Host range.

DNA is protected from restriction enzymes by which process?

Methylation.

What is/are the limiting factor(s) for viral infection?

The presence of specific receptor molecules on the host cell.

*If the infecting phage lacks some critical pieces of DNA necessary for replication it is called..

defective.

*Specialized transduction..

Involves the transfer of a few specific genes, utilized a defective virus, and only involves genes near the viral DNA integration site.

*Isometric phages such as phi X174..

Synthesize double-stranded DNA and single-stranded DNA, go through a lytic life cycle, and carry a positive single-strand of DNA.

What is the replicative form of nucleic acid in filamentous phages?

dsRNA.

*Filamentous phage...

Only infect E. coli that have pili.

*What is an example of a filamentous phage?

M13

T/F
The RNA phages contain only a single positive-sense strand of RNA.

True

T/F
A lysogenic cell contains viral DNA a prophage, integrated into the host chromosome.

True.

T/F
The integration of phage DNA into host DNA occurs in much the same fashion as seen in transformation, transduction, or conjugation.

True

T/F
Filamentous virus are incapable of causing a lytic infection.

True.

T/F
Completed filamentous phages are often found in the cytoplasm of infected bacteria.

False.

T/F
Virulent as well as temperate phages can serve as generalized transducing phages.

True.

T/F
Transduction often involves defective virus.

True.

T/F
The restriction-modification system always has two genes involved, the cutting enzyme and the methylating enzyme.

True

T/F
All single-stranded DNA phages are extruded.

False.

T/F
The host range of a virus depends on the presence of host receptor molecules.

True.

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