Chapter 13

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

+ssRNA

bacterial DNA degraded.

synthesis

Why is lysogeny advantageous to a bacteriophage?

the genetic material of the bacteriophage can be passed on to future generations of cells

Which of the following describes why viruses are not considered to be alive?

they lack cellular structure They cannot grow or respond to th the environment. Cannot reproduce on their own.

How are prions different from all other known infectious agents?

they lack nucleic acid

After a virus has invaded a cell, it takes control of the cell's metabolic machinery to produce more virions.

true

Animal viruses that are released by budding acquire a portion of the host cell membrane which becomes the viral envelope.

true

Human viruses can be difficult to treat because treatment might disrupt healthy cells also.

true

Oncogenes (genes that code for uncontrolled cell division) are genes that can cause cancer to develop. Viruses can carry copies of oncogenes in their genome and insert these genes into the host cell to cause cancer.

true

Replication of bacteriophages (viruses that attack bacteria) is described as either lytic or Lysogenic. The main difference in the two types of replication is in lysogenic replication the viral genomic material is inserted into the bacterial chromosome.

true

The HIV virus can become latent by using the enzyme reverse transcriptase to make a DNA copy of its +RNA genome that is then incorporated into hosts DNA.

true

The process by which a lysogenic phage is excised from the bacterial chromosome is called induction and can be started by ultraviolet light.

true

Viruses are primarily classified according to their

type of nucleic acid

Which of the following statements best describes a prion.

contains beta sheets and is a proteinaceous infectious agent

Which of the following describes why the chicken egg is used to grow human viruses.

inexpensive, largest of cells, sterile, and contain a nourishing yolk

This vrial nucleic acid can act directly as mRNA.

positive strand ssRNA

Double-stranded RNA genomes can be found

only in viruses

Which of the following types of animal virus requires RNA-dependent RNA transcriptase to be replicated?

-ssRNA

persistent viral infections

A virus that buds from a cell may allow the cell to remain intact for some time and The virses are slowly shed from the host cell.

which of the following is(are) correct about the lysogenic phage replication cycle?

Phage does not immediately take over the invaded cell. An inactive phage is called a prophage. The genome of the phage becomes part of the bacterial chromsome and is passed on to daughter cells.

In contrast to most dsDNA animal viruses, the poxviruses replicate solely in the cytoplasm of the host cell. This fact implies that the viral genome may encode

a DNA polymerase

During the intracellular state, a virus exists as

a nucleic acid

Viruses are shed slowly and steadily during

a persistent infection

Which of the following is not a difference between a bacteriophage and a virus that attacks animals?

animal viruses require chemical attraction to the hosts cell

A random process requiring little or no enzymatic activity.

assembly

Phages are nonmotile and make contact with host by random colliaion.

attachment

Which of the following events occurs in the lytic cycle of bacteriophage T4 infection but not in the lysogenic cycle?

digestion of host DNA

TheThe polio virus injects the viral genome into the animal cell.

direct penetration

Properties of viruses

do not divide or grow, not free living, acellular, replicate by using the host enzymes and organelles, and are obligate intracellular parasites

Replication takes place in the same manner that the hosts DNA is replicated

dsDNA

This type of virus causes most cases of diarrehea in infants.

dsRNA

Viruses can have genomes made up of nucleic acids which are not present in the genome of any cell. Which of the following types of nucleic acids are almost never found in cells?

dsRNA and ssDNA

The Adenoviruses and herpeviruses stimulate the cell to engulf the entire virus.

endocytosis

T4 uses lysozyme carried within the capsid to weaken petidoglycan cell wall.

entry

Which of the following would NOT be found as a component of a bacteriophage?

envelope

Lysogenic phages can change a pathogenic form of a bacterium into a harmless form.

false

Naked viruses always lyse the cell when being released.

false

The time of replication in both animal viruses and bacterial viruses is about 24 hours.

false

Viroids are small proteins that infect plants.

false

viruses come in many shapes and sizes they all have capsids made up of proteinaceous subunits and they all have a viral envelope that is acquired from the host cell.

false

Virus replication results in the death of the cell in a(n) __________ infection.

lytic

Measles and AIDs viruses fuse their membrane envelope with host cell membrane dump the capsid into host cell.

membrane fusion

This type of nucleic acid is not recognized by ribsomes so has to be converted.

negative sense ssRNA

The outermost layer of a virion fulfills which of the following functions of the virus?

protection and recognition

Which of the following is associated with the attachment of a bacteriophage to a bacterial cell?

random collisions, chemical attractions, and receptor specificity

Lysozyme completes work on cell walla and bacterium disintegrates.

release

Reverse transcriptase is associated with which of the following?

retroviruses

This type of virus uses reverse transcritase to make a DNA strand.

retroviruses

Before transcription takes place the host uses the viral nucleic acid as a templete to make a complementary strand of the viral nucleic acid.

ssDNA