Chapter 13: Characterizing & Classifying Viruses & Prions

When a bacteriophage infects hosts 19 cells and allows them to grow and replicate normally for many generations before lysis, this is considered _.

lysogeny

Assembly of enveloped viruses requires (membrane/matrix/receptor) to bring together the nucleocapsid and the envelope.

matrix

An animal virus that does not have an envelope is described as a(n) (naked/unenveloped/capsid) virion.

naked

The combination of a virus's protein coat and nucleic acid core is called the (capsid/virion/nucleocapsid).

nucleocapsid

Classification of viruses includes

orders and families.

Which of the following is a feature shared by viruses and living organisms? metabolic capability presence of cytoplasm responsiveness the ability to increase in size possession of a genome that directs synthesis of materials necessary for replication

possession of a genome that directs synthesis of materials necessary for replication

During a lytic replication cycle, what action does a phage take to ensure that its host bacterium does NOT continue synthesizing cellular molecules?

Phage enzymes degrade the bacterial DNA. By degrading the host DNA, the phage ensures that only phage proteins are synthesized.

In this stage of replication, the virion overcomes the cell wall barrier and cytoplasmic membrane and injects its genetic material into the bacterium cell.

entry

When the phenotype of a bacterium is changed via _, harmless bacteria can become pathogenic and are able to produce deadly toxins and proteins.

lysogenic conversion

In _, a phage is excised from the host chromosome via physical or chemical agents that damage the genetic material of the host.

induction

Host specificity of a virus is due to

interactions between viral and cellular surface molecules.

During the lysogenic cycle, it is possible for integrated phage genes to change the characteristics of the host cell. This is known as _____.

lysogenic conversion Lysogenic conversion involves phenotypic changes to the bacterium due to new genes from the integration of the phage genome.

Once entry into the bacterial cell has been achieved, the next step in a lytic replication cycle is _____.

synthesis Once the phage has entered a cell, viral protein synthesis begins.

Conventional genetic analyses of prions involving rRNA sequences are impossible because __________.

they do not contain nucleic acids

In this stage of replication, the phage is put together in the host cell. The capsid heads are made from capsomeres, the tails assemble and attach to heads, the tail fibers attach to tails, and this creates a mature virion.

assembly

The normal function of the PrP protein in mammals is believed to be:

assisting in normal synaptic development and function.

A phage T4 particle that has lost its tail fibers will have a replication cycle that is blocked at which of the following stages?

attachment

In this stage of replication, the virion comes in contact with the bacterium and the tailfibers bind to the receptors on the surface of the bacterium cell wall.

attachment

_ is another name for lysogenic phages that have a lysogenic replication cycle.

temperate phages

How is the HIV provirus different from a lambda-phage prophage?

the HIV provirus is integrated permanently into the host cell's DNA.

In a lytic cycle of replication, release of phages involves _____.

the bacterial cell bursting open The bacterial cell undergoes lysis, meaning that it is destroyed. Phages are then released.

Why is lysogeny advantageous to a bacteriophage?

the genetic material of the bacteriophage is amplified many times over that seen in a lytic phage.

A major difference between the lytic and lysogenic cycles of phage replication is that during the lysogenic phase _____.

the phage genome inserts itself into the host genome The phage DNA is integrated into the host DNA without destroying the cell.

How does the number of infectious prions increase?

Prions transform normal proteins into the misfolded beta-pleated sheet configuration; therefore, prions multiply by conversion.

Contact between a phage and its bacterial host occurs by _____.

a random collision Phages are incapable of movement, and thus are completely reliant on randomly colliding with a bacterium before attachment.

Which of the following is an accurate description of a virion? the protein portion of a viral particle the nucleic acid of a viral pathogen the nucleic acid of a viral pathogen inside a host cell the nucleic acid of a viral pathogen inside a host cell an infectious particle of protein and nucleic acid outside a host cell

an infectious particle of protein and nucleic acid outside a host cell

The process in which viral capsids are removed within the infected cell is called (entry/disassembly/uncoating).

uncoating

The viruses of fungi have RNA genomes and lack a capsid. They are therefore similar to

virioids

The genome of which of the following types of animal virus can act directly as mRNA?

+ssRNA viruses

Which of the following may occur in a lysogenic infection, but NOT a latent one? The viral DNA integrates (inserts) into the host cell DNA. The provirus/prophage directs the synthesis of viral proteins. The prophage/provirus alters gene expression in the host cell. The inserted viral DNA may leave the host DNA. The prophage/provirus is replicated with the host DNA.

The inserted viral DNA may leave the host DNA.

Why are the beta-pleated multimers of PrP potentially pathogenic?

The multimers are more stable and resistant to protease.

Which of the following is NOT a way in which viruses differ from all other living things? They do not grow. They live inside host cells. They cannot respond to environmental stimuli through metabolic changes. They cannot self-replicate.

They live inside host cells.

All members of a virus family have the same type of genome structure.

True

Bovine spongiform encephalopathy is an example of a prion disease.

True

Which of the following agents is capable of inducing conversion of a prophage to the lytic cycle? presence of +ssRNA UV light X-rays both UV light and X-rays both UV light and the presence of +ssRNA

both UV light and X-rays

Which test confirmed the presence of this prion disease?

brain scan The spongiform lesions noted on the brain scan are characteristic of prion diseases.

The process known as ________ is a mechanism of release for enveloped viruses.

budding

Parts of a bacteriophage

capside, tail sheath, tail fibers, baseplate with pins, envelope, glycoproteins

A 32-year-old father of two small children lived in the Midwestern United States. An avid hunter since childhood, the man visited annually with family and friends in Colorado for elk hunting. His job required frequent travel to Europe, where he enjoyed exotic foods. In 1988, his wife recalls, he began having problems. Frequently he forgot to pick up things from the store or even that his wife had called him. Later that year, he was unable to complete paperwork at his business and had difficulty performing even basic math. In England on business, he had forgotten his home phone number in the United States and couldn't remember how to spell his name for directory assistance. By September, his wife insisted he seek medical care. All the standard blood tests came back normal. A psychologist diagnosed depression, but a brain scan revealed spongiform changes. He was given six weeks to live because there is no treatment for this disease. What is the most likely etiology (cause) of this disease?

prion Prion diseases in a wide number of species are associated with spongiform changes in brain tissue.

An inactive bacteriophage is a _ that can remain in the host chromosome and render the bacterium resistant to additional infection by other similar viruses.

prophage

Which of the following is involved in the attachment of a bacteriophage to a bacterial cell? random collisions chemical attractions receptor specificity both chemical attractions and receptor specificity random collisions, chemical attractions, and receptor specificity

random collisions, chemical attractions, and receptor specificity

In this stage of replication, the mature virions exit the cell and lysis occurs.

release

Retroviruses require the activity of ________ to complete their infection cycle.

reverse transcriptase

Viruses can be grown in all of the following EXCEPT __________. live animals sterile nutrient agar embryonated eggs tissue culture

sterile nutrient agar

In this stage of replication, the virus' enzymes cause the bacterium to synthesize viral molecules instead of its own molecules. The steps involved in this stage can vary in complexity depending on what type of genetic material is housed in the viral capsid.

synthesis

How did this man most likely become exposed to this disease agent?

He is likely to have been exposed while hunting elk in Colorado during his childhood. Elk are part of the family Cervidae that have been shown to carry prions.

The enzyme lysozyme is critical for which of the stages of a bacteriophage T4 infection cycle?

entry and release

Is this disease contagious?

No, the disease is not contagious. There is no evidence that prion diseases are contagious. All have been associated with consuming tissues (especially neurological tissues, such as brain and spinal cord) of affected animals.

How do normal prion proteins (PrP) differ from the infectious prion proteins?

Normal PrP have alpha-helices; infectious PrP have beta-pleated sheets.

What portion of bacteriophage T4 enters E. coli?

Only the T4 genome enters the bacterial cell. The capsid remains on the surface of the cell, and the genome is the only portion to enter the cell.

Capsids functions to surround and protect the nucleic acid core.

True

Protozoa are susceptible to viral attack.

True

The genetic material of a virus can be DNA or RNA

True

The genomes of viruses are usually smaller than the genomes of bacteria.

True

Virus entry requires the presence of specific cell structures.

True

Viruses are not capable of metabolic activity on their own; they must have a host cell to reproduce.

True

Viruses can have different shapes.

True

What factor may induce a prophage to enter the lytic cycle?

UV light Ultraviolet radiation is known to cause the induction of prophage into the lytic cycle.

What is the typical incubation period for prion diseases?

decades Prion diseases are usually apparent decades after the initial exposure.

Which of the following events occurs in the lytic cycle of bacteriophage T4 infection but not in the lysogenic cycle? digestion and host DNA entry attachment viral protein synthesis both digestion of host DNA and viral proteins synthesis

digestion and host DNA

All viruses have both a capsid and an envelope.

False

All viruses use the host cell's nucleic acid polymerases for replication.

False

Capsids are acquired from the host cell during replication or release.

False

The intracellular state of a virus is called a virion.

False