Microbiology - Chpt. 6 - Unit 2

Viruses attach to their hosts via ______.

A. Host glycoproteins

A treatment for bacterial infections from the early 20th century has made a comeback; the use of bacterial viruses to eliminate bacterial infections. Which explanation most accurately describes the reason for the return of this treatment?

Antibiotic resistance in bacteria is on the increase, so using a different kind of therapy offers an alternative to traditional drugs.

Select the statement that most accurately describes the action of antimicrobial drugs today.

Antiviral drugs often result in toxic side effects due to their inhibition of host cell activity.

Sterilizing filters have a pore size of 0.22 μm. Which of the following statements is true?

Bacterial cells are typically between 1-10 μm and are blocked by the filter, whereas most viruses are between 20 and 200 nm and therefore pass through.

A/an _______ is the protein shell around the nucleic acid core of a virus.

Capsid

Which of the following is incorrect about prophages?

Cause lysis of host cells

During lysogeny, an inactive prophage state occurs when the viral DNA is inserted into the host ______.

DNA

Which of the following is not a characteristic of a transformed cell?

Decreased growth rate

Viral nucleic acid types include which of the following?

Double-stranded, DNA Single-stranded, DNA Double-stranded RNA, Single-stranded RNA. All of the choices are correct.

Which of the following is not associated with every virus?

Envelope

Animal viruses have the ability to attach to and enter almost any animal host cell.

False

Bacteriophages do not undergo adsorption to specific host cell receptors prior to penetration.

False

Each virus is classified into a genus based on its host, target tissue, and type of disease it causes.

False

The adeno-associated virus (AAV) and the delta agent are prions.

False

Viral nomenclature uses the same system as living organisms; a genus and specific epithet is designated for each virus.

False

Viruses are considered ultramicroscopic because they range in size from 2 mm to 450 mm.

False

Viruses are not filterable.

False

Which of the following represents a virus family name?

Herpesviridae

Host cells of viruses include ______.

Humans and other animals, plants and fungi, bacteria, protozoa and algae. All of the choices are correct.

Which of the following is/are type(s) of cytopathic effects?

Inclusions in the nucleus, Multinucleated giant cells, Inclusions in the cytoplasm, Rounding of cells, All of the choices are correct.

The event that occurs in bacteriophage multiplication that does not occur in animal virus replication is ______.

Injection of only the viral nucleic acid into the host cell

Which of the following will not support viral cultivation?

Live lab animals, Embryonated bird eggs, Primary cell cultures, Continuous cell cultures, All of the choices will support viral cultivation

When a bacterium acquires a trait from its temperate phage, it is called ______.

Lysogenic conversion

Who developed a rabies vaccine after realizing the disease was caused by something smaller than a bacterium?

Pasteur

How are viroids transmitted?

Plant seeds

Why do some animal viruses have an external envelope, while bacteriophages never do?

Some animal viruses bud out, taking part of the plasma membrane with them, whereas phages always lyse the host bacterial cell when they exit.

Successful anti-HIV drug therapies today work by blocking the action of viral reverse transcriptase. Select which step of virus multiplication that would be directly blocked by this mechanism.

Synthesis

What structures are used by bacteriophages to attach to host cell receptors?

Tail fibers

Tamiflu is a common medication given for influenza treatment. It works by protecting and blocking sialic acid molecules on the surfaces of host cells and influenza virus envelopes as they leave the cell. Which statement reflects the mechanism of Tamiflu's action?

Tamiflu interferes with the release of the budding viruses from the infected host cells.

What type of phage enters an inactive prophage stage?

Temperate

Which of the following is not a typical capsid shape?

Tetrahedral

A treatment for bacterial infections from the early 20th century has made a comeback; the use of bacterial viruses to eliminate bacterial infections. Which explanation most accurately describes the mechanism of action behind this treatment?

The attachment structures on the virus and the receptors on the host cells make for exquisite specificity of viruses for particular bacterial species.

Which of the following is a true statement regarding lysogeny?

The host bacterial cell acquires new characteristics that are often detrimental to humans.

A fully formed virus that can cause an infection in a host cell is called a virion.

True

Prophages can be activated into viral replication and enter the lytic cycle.

True

Spikes are glycoproteins that can be found projecting from the viral capsid.

True

Using species names for viruses is controversial since viruses are not considered living organisms, and they change over time so characteristics that may be used for speciation are unstable.

True

Viral spikes are inserted into the host cell membrane before budding or exocytosis.

True

Viruses are simple, noncellular, lacking mRNA and ribosomes

True

Viruses are the most common cause of acute infections that do not result in hospitalization.

True

Viruses are unable to multiply outside of a host cell

True

Viruses are used to produce vaccines for prevention of certain viral infections.

True

Viruses mutate, and some viruses have not been discovered.

True

When a virus enters a host cell, the viral genes redirect the genetic and metabolic activities of the host cell.

True

Which of the following is not a viral order in the classification system?

Vaccinia virus

The correct sequence of events in viral multiplication is ________.

adsorption, penetration, uncoating, synthesis, assembly, and release

You are working in a laboratory that is studying a newly isolated virus. Your job is to culture the virus using in vitro methods. Upon observing your inoculated tissue culture specimen one day, you notice clumps of cells growing on top of the original monolayer of cells. Microscopic analysis of stained cells from the culture reveal an alteration in host cell membrane protein content and chromosomal structure. Based upon this information, you hypothesize that the virus you are studying is ______.

an oncovirus

Diagnosis of viral infections sometimes involves analyzing the patient's blood for specific _____ that the immune system produces against the virus.

antibodies

Viral spikes ________.

are always present on enveloped viruses

Viruses that infect bacteria are specifically called ______.

bacteriophages

Classification of viruses into families involves determining all the following characteristics except ________.

biochemical reactions

Viruses ______.

cannot be seen in a light microscope

Helical and icosahedral are terms used to describe the shape of a viral ______.

capsid

Viral capsids are made from subunits called ______.

capsomeres

A common method for cultivating viruses in the lab is to use in vitro systems called _____ cultures

cell

Persistent viruses that can reactivate periodically are ______.

chronic latent viruses

Satellite viruses are _______.

depend on other viruses for replication

Uncoating of viral nucleic acid _______.

does not occur in bacteriophage, multiplication involves enzymatic destruction of the capsid, occurs during penetration in the multiplication cycle, occurs before replication, All of the choices are correct.

The core of every virus particle always contains ______.

either DNA or RNA

One of the principal viral capsid shapes is a 20-sided figure with 12 evenly spaced corners referred to as a/an _______ capsid.

icosahedral

In transduction, the viral genome _______.

includes DNA from the previous host

The activation of a prophage is called ______.

induction

T-even phages ______.

infect Escherichia coli cells

The envelope of enveloped viruses _______.

is obtained by viral budding or exocytosis

The primary purpose(s) of viral cultivation is/are to _______.

isolate and identify viruses in clinical specimens, prepare viruses for vaccines, do detailed research on viral structure, lifestyle, genetics, and effects on host cells, perform wide-scale harvesting of viruses, All of the choices are correct.

Viruses that cause infection resulting in alternating periods of activity with symptoms and inactivity without symptoms are called ______.

latent

All of the following pertain to virus envelopes except ________.

located between the capsid and nucleic acid

New, nonenveloped virus release occurs by ______.

lysis

Oncogenic viruses include all the following except ______.

measles virus

Viruses exhibit all the following except _

metabolism

Cells grown in culture form a/an ______.

monolayer

In order to replicate within a host cell, a virus with a genome comprised of single-stranded positivesense RNA ______

must use its genomic strand as a template to make copies of negative-sense RNA for packaging

In order to synthesize proteins, a virus with a genome comprised of single-stranded negative-sense RNA _______.

must use its negative-sense strand as a template to make a positive-sense RNA

A naked virus only has a/an ______.

nucleocapsid

In general, most DNA viruses multiply in the host cell's _____, while most RNA viruses multiply in the host cell's _____.

nucleus; cytoplasm

Mammalian viruses capable of starting tumors are ______.

oncoviruses

Visible, clear, well-defined patches in a monolayer of virus-infected cells in a culture are called ______.

plaques

Viral growth in bird embryos can cause discrete, opaque spots in the embryonic membranes called ______.

pocks

Viruses with _____-sense RNA contain the correct message for translation, while viruses with _____-sense RNA must first be converted into a correct message.

positive; negative

Freshly isolated animal tissue that is placed in a growth medium and allowed to produce a cell monolayer is referred to as a/n _____ cell culture.

primary

Infectious protein particles are called ______.

prions

Two noncellular agents, smaller than viruses, are infectious proteins called _____ and infectious RNA strands called _____.

prions; viroids

Viruses acquire envelopes around their nucleocapsids during ______.

release

A negative RNA virus must first ________.

synthesize a positive RNA copy of its genome

Lysogeny refers to _______.

the viral genome inserting into bacterial host chromosome

Viral tissue specificities are called ______.

tropisms

Host range is limited by the _______

type of host cell receptors on cell membrane

The process of dissolving the envelope and capsid to release the viral nucleic acid is ______.

uncoating

Reverse transcriptase synthesizes ________.

viral DNA from RNA

Infectious naked strands of RNA that affect plants are called ______.

viroids

Viral classification has changed over the years and while they are given genus names, the use of species names has not been widely accepted. This is because ________.

viruses are not organisms, viruses change over time making species characteristics difficult to stabilize, viruses that could be classified into a single species may have many, but not all, properties in common, All of these choices are arguments against using species designations for viruses.

Antiviral drugs are often difficult to develop, largely because ________.

viruses are obligate intracellular parasites so the drugs must enter the host cell and often cause toxic side effects in order to destroy the virus

Compared to bacteria that have a typical size range between 1-10 μm, _______.

viruses have a much greater size range; between 22 nm and 1000 nm

Which of the following occurs during assembly?

A nucleocapsid is formed and viral spikes insert in host cell membrane.

Some animals can become infected with multiple influenza virus strains usually associated with other animals. Which statement below describes the result of these infections?

A new novel strain of flu may be produced, for which the human population has no immunity, Major genetic variations in the flu viruses can be reproduced, The viral genomes within the host cells can become recombined, All of the choices are correct.

Creutzfeldt-Jacob disease is _______.

a spongiform encephalopathy of humans