Micro Exam Chapter 13

Why is it not surprising that AIDS patients frequently suffer a viral-induced tumor?

HIV genomes integrate into the host cell chromosome. This integration might result in loss of control of the cell cycle (also known as cancer).

Explain why HIV becomes resistant so quickly when a single drug is used therapeutically.

HIV uses reverse transcriptase to make a cDNA version of its RNA genome. This polymerase is "'sloppy," with a high rate of error and lack of a proofreading capability. This leads to a high rate of mutation of the viral genome and increased chance for drug resistance.

Most temperate phages integrate into the host chromosome, whereas some replicate as plasmids. Which kind of relationship do you think would be more likely to maintain the phage in the host cell, and why?

Integration, because plasmids are frequently lost during cell division, which could leave a daughter cell without the virus genome.

The concentration of virus that infects or kills 50% of the host cells is referred to as the

LD50 AND ID50

Would ID50 and LD50 necessarily be the same for a given virus? Why or why not?

No, because a virus may be highly infectious (very low ID50 value) but only marginally lethal (very high LD50 value), for example the rhinovirus (common cold virus).

Would you expect the number of virions to be the same if you measured them by the plaque assay or by counting using the electron microscope? Why?

No—the plaque assay only measures viable virus particles, while the electron microscope cannot distinguish between defective and viable virus.

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

Protein fibers at the end of the phage tail.

For which of the following processes are enzymes not required?

Self-assembly

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

T4

TRUE OR FALSE: A filamentous phage is incapable of causing a lytic infection.

TRUE

TRUE OR FALSE: Transduction often involves defective virus.

TRUE

TRUE OR FALSE: Viruses that cause acute infection result in productive infections.

TRUE

What part of the attached bacteriophage enters through the host cell wall?

The nucleic acid.

You add an unknown phage to a mixture of F+ and F− cells of E. coli and plate out the bacteria. The bacterial colonies that grow are all F−. How can you explain this phenomenon?

The phage bound to a receptor on the sex pilus, and therefore only infected the F+ cells (leaving the F− cells alone).

Which of the following is not a characteristic of normal cells?

They grow as multiple layers.

Phage-encoded proteins are

coded for by phage DNA AND early proteins.

A virion is a(n)

complete, extracellular virus particle.

The best known chronic infection involves

hepatitis B.

Normal tissue taken from animals and prepared immediately as a medium for viral growth is termed a(n)

primary culture.

A virion is composed of

protein, either RNA or DNA, and possibly lipid.

During attachment of phage to E. coli, the phage

randomly bumps into the bacteria AND attaches to proteins or carbohydrates on the bacterial surface.

The terms helical, icosahedral, and complex refer to

shapes of viruses.

The filamentous phages all contain

single-stranded DNA.

Attachment of animal viruses to the host cell may be by means of

spikes.

The genome of retroviruses is made of

ssRNA.

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

temperate phages.

During penetration of E. coli by the T4 phage,

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

True or false: If a virus utilizes a lytic life cycle of reproduction, it will not induce tumors.

true

True or false: Non-enveloped and enveloped viruses both may enter the host via endocytosis.

true

True or false: transduction often involves defective virus

true

true or false: the integration of phage DNA into host DNA occurs in much the same fashion as seen in transformation, transduction, or conjugation.

true

Spongiform encephalopathy occurs in all of the following EXCEPT

plants.

Viroids cause disease in

plants.

There are ______ major families of RNA containing viruses that infect vertebrates.

13

There are ______ major families of DNA-containing viruses that infect vertebrates.

7

Which statement regarding phage replication is TRUE?

A lysogen is a bacterial cell with an integrated prophage.

Why do animal viruses have envelopes and phages rarely do?

Animal viruses will often use the envelope in order to fuse with the plasma membrane of a new target cell, gaining entry into the cytoplasm.

Which does not refer to the shape of a virus?

Bacillus

What are two ways that phage can replicate without directly lysing their host cell?

Extrusion and lysogeny

TRUE OR FALSE: Completed filamentous phages are often found in the cytoplasm of infected bacteria.

FALSE

TRUE OR FALSE: Infective and non-infective viruses may be distinguished by growth on MacConkey's agar.

FALSE

Why is it virtually impossible to eradicate a disease caused by a zoonotic virus?

You would have to drive the vector organism extinct to do so. Many vector organisms have multiple stages of their life cycle that can carry a zoonotic virus, which complicates controlling the vector-borne transmission. Many viruses transmitted in this manner may utilize more than one vector organism. Many zoonotic viruses may be able to reside in more than one host organism, complicating control measures.

The site at which a virus has infected and subsequently lysed the infected cell, releasing its progeny to infect and lyse surrounding cells, thereby forming a "clear zone," is

a plaque.

Diseases of short duration frequently followed by long-term immunity are referred to as

acute infections.

If you had three tubes of flu viruses and you exposed tube 1 to protease, tube 2 to protease and RNase, and tube 3 to protease and DNase, and the contents of tube 2 were be degraded, you would be able to conclude that

an RNA virus.

Prions are

an infectious protein.

Genetic exchange in segmented viruses that allows a zoonotic virus to infect humans is an example

antigenic shift.

Transducing virulent phages do not lyse the cells they invade because

bacterial DNA has replaced critical viral DNA in the phage.

Viruses are not cultivated in

blood agar.

In addition to lysis, animal viruses may exit the host cell by

budding.

The shape of the virus is determined by its

capsid.

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

certain phage genes are repressed.

Entry of bacteriophages and animal viruses into host cells

differs because bacteriophages leave the capsid outside the cell, while animal virus entry involves the entry of the whole nucleocapsid.

Viruses are commonly referred to by their ______ name.

disease AND species

If reasonably pure preparations of virus are available, the number of virus present may be determined by

electron microscopy.

When a non-enveloped animal virus adsorbs to the host cell with its protein spikes, the virions are taken into the cell by the process of

endocytosis.

The viral envelope closely resembles the

eukaryotic cytoplasmic membrane.

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

extrusion.

True or false: capsids are made of a number of capsomeres that are covalently bonded to one another.

false

true or false: Capsids are made of a number of capsomeres that are covalently bonded to one another.

false

The bacterial viruses that are released by a process termed extrusion are called

filamentous phages.

The enveloped viruses typically obtain their envelope

from the host cytoplasmic membrane as they exit the host.

Enveloped viruses

have a lipid bilayer membrane containing various proteins.

Which of the following BEST describes the protein coat of a virus? It

is called a capsid, protects the nucleic acid, AND is involved in the recognition of host cell receptors by non-enveloped viruses.

Once inside the host cell, phage DNA

is replicated, is replicated, may get degraded by bacterial nucleases, and may integrate into the host chromosome.

All of the statements about specialized transduction are correct EXCEPT

it involves the random transmission of any gene.

In the region of budding, the inside of the cytoplasmic membrane becomes coated with

matrix proteins.

A temperate phage

may be lysogenic AND enters a lysogenic or lytic life cycle shortly after entering the host cell.

The term "segmented" refers to viruses that

may contain several pieces of RNA.

Carriers

may have a persistent infection AND may be a source of infection.

Using phages to treat a bacterial infection is an interesting idea because

of the increasing problem of antibiotic resistance in pathogens.

Filamentous phages

only infect E. coli that have pili.

An infection in which the virus is continually present in the body is referred to as

persistent