Chapter 13: Viruses, Viroids, and Prions

Which of the following can cause a phage in the lysogenic stage to revert to the lytic stage?

UV light

The stage of T4 replication that involves interaction between the protein fibers on the phage and receptors on the bacterial cell wall is the

attachment stage

Viruses that infect bacterial cells are called ______.

bacteriophages

In virology, a plaque is a(n)

clearing in a lawn of bacteria

Please choose the term that describes a virus that has a lipid bilayer (derived from the host cell) surrounding its capsid.

Enveloped virus

What term describes the type of bacteriophage infection cycle where the bacteriophage DNA is inserted into the host cell DNA as a prophage and the infected bacteria can continue to grow and divide?

Lysogenic

Virulent phage

Phage that lyses the bacterial host when completing its life cycle.

A difference between plasmids and fragments of DNA that have been transferred between cells is

plasmids can replicate independently

In viral entry by endocytosis

the host cell's cytoplasmic membrane surrounds the whole virion and forms a vesicle.

T or F: The enzyme lysozyme is used by the T4 phage to assist in the injection of its DNA into the target cell.

True.

T or F: Both enveloped and non-enveloped (naked) viruses can enter a cell by endocytosis.

True. Both enveloped and non-enveloped (naked) viruses can enter a cell by endocytosis.

T or F: In order for viruses to enter host cells, they must bind to receptors on the host cytoplasmic membrane.

True. No matter how a virus enters the host cell (fusion or endoxytosis), the first step for entry is binding to host cell receptors.

T or F: Bacteriophage DNA directs the degradation of the bacterial host cell's DNA.

True. Once inside the cell, the virus takes over the cell and degrades the host cell DNA.

T or F: Almost immediately upon entry, the viral nucleic acid alters the gene expression of the host cell.

True. The viral nucleic acid alters the gene expression of the host cell soon after infection.

T or F: More than one mechanism of viral entry into a host cell exists

True. Viruses can enter a host cell by membrane fusion (enveloped viruses) or by endocytosis (non-enveloped or enveloped viruses).

A major difference in the replication of animal viruses and bacteriophages is the ______ step.

penetration

After host cell DNA is broken down by a viral enzyme

phage DNA is replicated and phage coat proteins are produced.

During viral infection of a host cell, which is the third step of the process?

Release of nucleocapsid into host cytoplasm

Please order the following steps to reflect the order in which they occur in the replication cycle of an animal virus. - Assembly of viral particle - Penetration and uncoating - Adsorption (attachment) to host cell surface - Synthesis of viral nucleic acid and proteins - Release from host cell

1. Adsorption (attachment) to host cell surface 2. Penetration and uncoating 3. Synthesis of viral nucleic acid and proteins 4. Assembly of viral particle 5. Release from host cell

Place the steps of T4 phage replication into the correct sequence. - Synthesis—phage genome is transcribed and translated; phage DNA is replicated. - Assembly—newly synthesized phage components are assembled into mature virions. - Genome entry—phage tail contracts and phage DNA is injected into bacterial cell. - Release—bacterial cell lyses, releasing new infectious virions. - Attachment—phages attach to receptors on bacterial surface.

1. Attachment—phages attach to receptors on bacterial surface. 2. Genome entry—phage tail contracts and phage DNA is injected into bacterial cell. 3. Synthesis—phage genome is transcribed and translated; phage DNA is replicated. 4. Assembly—newly synthesized phage components are assembled into mature virions. 5. Release—bacterial cell lyses, releasing new infectious virions.

Which of the following is required to maintain a lysogenic state?

A repressor protein

The advantageous genes that can be transferred by transduction are genes for - sugar fermentation. - toxin production. - drug resistance. - All of the answer choices are correct. - None of the answer choices is correct.

All of the answer choices are correct

In animal virus replication, an uncoating step is needed to release the nucleic acid from the capsid. Why is this step not needed in bacteriophage replication?

Bacteriophages inject their DNA into the host cell.

What bacterial enzyme is used by the virus for replicating its nucleic acid?

DNA polymerase

T or F: T-even phages can replicate independently of a host cell.

False. All viruses require host cell machinery in order to replicate.

T or F: In the lysogenic stage of phage replication, the host cell is lysed.

False. At the lysogenic phase, the virus DNA integrates into the host cell genome.

T or F: All viruses can infect any cell type or tissue type.

False. Because a virus must attach to host cell cytoplasmic membrane receptors for entry into that cell, a virus may only be able to infect a single or a limited number of cells or tissues (tissue tropism).

How does bacteriophage DNA get into the host cell?

It is injected

Which of the following describes a latent viral infection?

Long periods of time with essentially zero viral replication, punctuated by outbreaks of active replication and disease manifestation. Infected individuals are largely non-infectious between outbreak periods.

When present, of what is the viral envelope composed?

Mainly lipids

Temperate phage

Phage that is able to incorporate its genome into the host chromosome.

A bacteriophage initially associates with which bacterial structure?

The bacterial cell wall

Generalized transduction

Transduction resulting from a packaging error.

Specialized transduction

Transduction resulting from an error in excision of a prophage.

Generalized transduction occurs when

a bacteriophage packages a piece of bacterial DNA during replication.

During maturation or formation of phage particles

a few phage heads may surround fragments of host bacterial DNA.

The capsid of a virus is

a protein shell that surrounds the nucleic acid.

The general steps in viral replication (in order) are

adsorption, penetration, synthesis, assembly, release.

The basic parts of a bacteriophage are

an isohedral head, tail, tail pins, and fibers

Viral spikes

attach specifically to host cell receptors

Every virus particle contains ______.

either DNA or RNA

The phages T4 (lytic) and lambda (temperate) share all of the following characteristics EXCEPT

existing as a prophage.

In transduction, bacterial DNA is transferred to a new cell when

it is injected by the virus.

The final step in T2 bacteriophage infection results in:

lysis of the bacterial cell and release of new viral particles.

Bacteriophages involved in generalized transduction are ______ phages

lytic

Viral cycles that end in release of the new phages and immediate destruction of the host bacterial cell are referred to as ______.

lytic

What term describes the type of bacteriophage infection in which the host bacteria are lysed and killed as a result of the infection?

lytic

Once inside the host cell, viral DNA directs production of _______.

new viral particles

Viral capsids are composed of ___________.

protein

Phage DNA encodes for the proteins of the viral capsid and

regulatory proteins that direct the production and assembly of the capsid proteins.

All of the following could serve as receptors for phage attachment EXCEPT

ribosomes

Removal of the capsid to release the virus nucleic acid into the host cytoplasm is called ______.

uncoating.

Acute infection

Infection in which a virus multiplies rapidly and spreads in the host.

Please choose the statement that best describes the role of viral surface proteins or spikes.

Viral spikes provide means of attachment to host cell surface.

After entry of the bacteriophage into the host cell, a phage enzyme

breaks the host DNA into fragments.

Bacteriophages adsorb or attach

only to members of the same bacterial species

In lytic phage infections, the early viral proteins are important for initial steps of phage multiplication. Which of the following are functions of these proteins? - Degrade host cell's DNA. - Modify host cell's RNA polymerase so that it doesn't recognize bacterial promoters. - Degrade host cell's ribosomes. - Activate bacteriophage's DNA polymerase for copying bacterial RNA.

- Degrade host cell's DNA. - Modify host cell's RNA polymerase so that it doesn't recognize bacterial promoters.

Please select the methods that are used to cultivate animal viruses. - Use of cell culture techniques - Use of enriched agar media - Use of animal inoculation - Inoculation of embryonated eggs - Use of enriched broth media

- Use of cell culture techniques - Use of animal inoculation - Inoculation of embryonated eggs

The T-even bacteriophages such as T2 and T4 infect

Escherichia coli.

T or F: Generalized transduction is so called because specific bacterial genes are transferred during this process.

False. In generalized transduction, any segment of bacterial DNA can be transferred. During specialized transduction, specific genes are transferred, depending on where the viral DNA is integrated into the bacterial chromosome.

T or F: Generalized transduction involves the transfer of phage genes from one bacterial cell to another.

False. The genes that are transferred are bacterial genes.

T or F: Once a phage becomes lysogenic, it will remain lysogenic and never be lytic again.

False. The virus may revert to a lytic stage if the host cell is exposed to a DNA-damaging agent such as UV light.

What are the two entry mechanisms used by enveloped viruses?

Fusion and endocytosis

When the bacteriophage transfers bacterial DNA into a recipient bacterial cell, this DNA

can integrate into the chromosome.

Expression of viral oncogenes in infected animal cells

can mimic proto-oncogenes, causing imbalance in cell cycle control towards unchecked proliferation, leading to tumor formation.