Chapter 13: Viruses

Viruses are best described as _______.

infectious agents

Human cells are larger than viruses by which size factor?

Thousand;

Human cells are approximately 1 thousand times larger than viruses.

A _______ is a single virus particle.

virion

Which of the following statements about virus nucleic acid is true?

Viruses contain either DNA or RNA.

The viral genome is protected from the environment by a protein shell called the ______.

capsid

Which of the following statements about viruses are true?

1) Viruses contain RNA or DNA but not both.

2) Viruses contain both DNA and RNA in one capsid.

3) The viral capsid is composed of carbohydrates.

4) The viral capsid is composed of protein.

1) Viruses contain RNA or DNA but not both.

4) The viral capsid is composed of protein.

At a minimum, all viruses are composed of ______.

1) proteins

2) Lipids

3) carbohyrates

4) nucleic acids

1) proteins

4) nucleic acids

The smallest virus is approximately 10 ______ in diameter.

nanometers

Many animal viruses have proteins called _____ that attach to receptors on host cells.

spike

A complete viral particle, which typically consists of nucleic acid surrounded by a protein coat, is called a(n)

virion

Enveloped viruses have an outer layer made up of _______.

lipid

Viral genomes can be ______.

either single-stranded or double-stranded

A capsid is ______.

protein coat that surrounds the viral genome

In enveloped viruses, sandwiched between the nucleocapsid and the envelope is the ______.

matrix protein

The nucleocapsid is composed of ______.

DNA or RNA and protein.

There is no need to classify viruses because they are not living organisms.

False;

Although viruses are not living, classification is still important for identification and study.

The viral proteins that stick out from either the lipid bilayer of enveloped viruses or the capsid of non-enveloped viruses, and attach to host cells, are ______.

spikes

Naked viruses do not have an outer lipid bilayer. These viruses are called _____ _____ viruses.

non-enveloped

Which of the following describe a type of relationship that bacteriophages can have with their host?

1) Latent infection where the host cell lyses

2) Latent infection where host cell genotype is changed

3) Productive lytic infection

2) Latent infection where host cell genotype is changed

3) Productive lytic infection

Bacteriophages that exit the host cell at the end of an infection by lysing it are called _______ phages.

virulent

The phospholipid bilayer found surrounding the capsid of some viruses is the ______.

envelope;

Some enveloped viruses have a protein layer called a matrix that is sandwiched between the capsid and envelope.

This image shows the attachment stage of the T4 phage lytic cycle.

Which of the following about classifying viruses is FALSE?

1) An online database classifying viruses is kept by the ICTV (International Committee on Taxonomy of Viruses).

2) It is not as important as classifying organisms since they are not living entities.

3) It provides a useful way to identify and study viruses.

4) Viruses can be classified based on different viral characteristics.

2) It is not as important as classifying organisms since they are not living entities.

How does bacteriophage nucleic acid enter the host cell?

Injection

Match each possible outcome of phage replication with the correct definition.

1) Productive infection

2) Latent state

-Productive infection -> new viral particles are produced

-Latent state -> viral genome remains silent within the cell

This figure highlights a stage of the T4 phage lytic cycle known as synthesis

synthesis

lipid

Infection of bacteria by ____ phages always ends with the lysis of the host cell.

lytic

In which phase of the T4 phage lytic cycle are new phage particles put together?

Assembly

The binding of a bacteriophage surface protein to a host cell receptor is called ______.

attachment

In this figure, the genome entry stage of the T4 phage lytic cycle is shown.

Bacteriophages that can enter into a lytic cycle or a lysogenic cycle are called _____ phages

temperate

Phage DNA and proteins are made during the _____ step of the T4 lytic cycle.

synthesis/biosynthesis

In a lysogenic infection, the phage DNA that is incorporated into the bacterial host genome is called a ______.

prophage

Replication of temperate phages and lytic phages have which steps in common?

1) Integration of the viral genome into the host genome

2) Attachment

3) Genome entry

4) Release

5) Assembly

6) Biosynthesis of viral components

2) Attachment

3) Genome entry

4) Release

5) Assembly

6) Biosynthesis of viral components

The ____ or maturation stage of the T4 phage lytic cycle is marked by the formation of new phage particles inside of the host cell.

assembly

In a lysogenic infection, ______.

the bacteriophage DNA integrates into the host chromosome

A ______ phage can either cause a lytic infection or can incorporate its DNA into the host genome as a prophage.

temperate

Consequences of lysogeny include ______.

1) immunity to superinfection

2) lysogenic conversion

3) morphological changes

4) phage induction and conversion

1) immunity to superinfection

2) lysogenic conversion

Lysogeny is best described as ______.

integration of the viral genome into the host chromosome

______ is a change in the phenotype of a lysogen as a consequence of the specific prophage it carries.

Lysogenic conversion

During the process that leads to a lysogenic infection, which of the following inserts the phage DNA into a bacterial chromosome?

integrase

Some lysogenic phages can increase the pathogenicity of their bacterial host.

True

A ______ infection results from the integration of bacteriophage DNA into the chromosome of the bacterial host.

lysogenic

Bacteriophages play a fundamental role in a type of horizontal gene transfer called _____

transduction

Lysogens are more susceptible to reinfection by the same type of phage.

false

Which form of transduction results from packaging errors during phage assembly?

Generalized;

Which of the following describes a consequence of lysogeny that could result in human disease?

Lysogenic conversion;

Recall that a lysogen contains phage genes. These may confer new characteristics on the lysogen - for example, the ability to produce a toxin that causes human disease. Host cell lysis is not a consequence of lysogeny.

Which form of transduction results from excision errors during the transition from a lysogenic to lytic cycle?

Specialized

Some pathogenic bacteria produce toxins that are encoded on prophage DNA, and these are examples of _____ conversion.

lysogenic

A generalized infection cycle of an animal viruses can be divided into five steps: 1. _____; 2. ____ entry ; 3____; 4. assembly; and 5.

1) attachment

2) genome entry

3) synthesis

4) assembly

5) release

Which of the following phage types cause productive infections that do not kill the host cell?

1) Virulent

2) Lytic

3) T4

4) Filamentous

Filamentous

Attachment of animal viruses to the host cell typically occurs by means of ______.

spikes

What term is used to describe the transfer of genetic information from one bacterium to another bacterium by a bacteriophage?

transduction

When an enveloped virus gains entry to an animal cell by fusion, the virus envelope fuses with the ______.

cytoplasmic membrane

_____ transduction is the result of packaging errors during the assembly stage of phage replication.

generalized

Which of the following processes are required for production of virus particles in a host cell?

1) Replication of viral genome

2) Translation of viral genes

3) Replication of host genome

4) Cleavage of host polypeptides

5) Transcription of viral genes

1) Replication of viral genome

2) Translation of viral genes

5) Transcription of viral genes

_____ transduction is the result of excision errors made as temperate phages transition from a lysogenic to a lytic cycle.

specialized

The replication strategy of viruses can be divided into three general categories: those used by ______.

1) enveloped viruses

2) reverse transcribing viruses

3) DNA viruses

4) RNA viruses

2) reverse transcribing viruses

3) DNA viruses

4) RNA viruses

List the steps of an animal virus infection cycle in the correct order. Start with the earliest at the top.

-penetration&uncoating

-assembly

-synthesis of viral proteins and replication of the genome

-release

-attachment

1. attachment2. penetration and uncoating3. synthesis of viral proteins and replications of the geonome4. assembly5. release

DNA viruses often encode their own DNA _____ for DNA synthesis, which allows them to replicate even if the host cell is not actively duplicating its own chromosome.

polymerase

In the case of animal viruses, the molecules that viral spikes attach to on the host cell in order to gain entry are typically ______.

glycoproteins

Most animal DNA viruses replicate within the host cell's ______.

nucleus;

DNA is replicated within the nucleus of eukaryotes.

The process by which a virus is taken up by a host cell as a result of the host cell's cytoplasmic membrane surrounding the virion to form a vesicle is called ______.

endocytosis

The replication scheme of double-stranded DNA viruses ______.

follows the central dogma of molecular biology

All of the following are required for synthesis of new virus particles in a host cell EXCEPT ______.

homologous recombination

The replication strategies of animal viruses can be divided into three general categories: those used by ____ viruses, ____ viruses, and reverse transcribing viruses.

DNA; RNA

DNA viruses can only replicate when the host cell is replicating its own genome.

False; Many DNA viruses encode their own DNA polymerase and can replicate even if the host cell is not replicating.

The virally encoded polymerase needed for replication of RNA viruses is called a

replicase

In animals, replication of most DNA viruses occurs within the host cell's

nucleus

During viral replication, when the genome of a (+) single-stranded RNA virus is used as a template, which of the following is generated?

(-) single-stranded RNA molecules

Replication of single-stranded DNA viruses is quite similar to that of double-stranded DNA viruses, except that ______.

a complement to the single-stranded DNA molecule must be synthesized

Mutations in the influenza virus genome can result in minor changes in key viral surface proteins. This type of variation is called antigenic _____

drift

The enzyme of RNA viruses that typically lacks proofreading ability and thus makes many mistakes compared to the polymerases of DNA viruses is ______.

replicase

When two different strains of a segmented virus enter the same cell, reassortment of the gene segments can occur, resulting in ______.

antigenic shift

Replicases are ______ polymerases.

RNA-dependent RNA

In ______-strand RNA viral genomes, the genome functions as an mRNA molecule.

(+);

Positive sense means that the RNA can be immediately translated.

Reverse transcriptase is a(n) ____ polymerases.

Reverse transcriptase is a(n)

Viruses that have an RNA genome and use reverse transcriptase to synthesize a DNA copy of that genome are called ______.

retroviruses

The accumulation of mutations in genes that encode viral surface proteins recognized by the immune system results in a type of antigenic variation called ______.

antigenic drift

antigenic shift

Recall that antigenic shift occurs as a result of genetic reassortment between two viruses.

Which of the following describes the various viral parts coming together to produce virions?

Assembly

RNA viruses have a higher mutation rate than DNA viruses because replicases typically lack ____ ability.

proofreading

The stage of viral multiplication at which budding occurs is ______.

release

Reassortment of gene segments that encode viral surface proteins recognized by the immune system can result in a loss of the immune system's ability to recognize and respond to the virus. This phenomenon is called antigenic ____.

shift

An enzyme that uses an RNA molecule as a template to make a complementary copy of DNA is called ______.

reverse transcriptase

HIV is described as a ____ because it uses reverse transcriptase to make a DNA copy from its RNA genome.

retrovirus

Which are the two major categories of viral infections

1) Chronic

2) Acute

3) Latent

4) Persistent

5) Asymptomatic

2) Acute

4) Persistent

During the _____ or maturation step in viral multiplication, capsids and genetic material are packaged into virions.

assembly

Symptoms of acute viral diseases result from ______.

1) viral budding

2) host immune response

3) host tissue damage

4) lysogenic conversion

2) host immune response

3) host tissue damage

Which types of viruses are released by budding?

Enveloped viruses

____ infections remain for years, or even the lifetime of the host, sometimes without any symptoms.

persistent/chronic

An abnormal growth of tissue resulting from a malfunction in the normally highly regulated process of cell growth is a

antigenic shift

An abnormal growth of tissue resulting from a malfunction in the normally highly regulated process of cell growth is a ____.

tumor

Reverse transcriptase is a(n) ______ polymerase.

RNA-dependent DNA

Oncoviruses are viruses that can ______.

cause cancer in humans

The major categories of animal viral infections are ____ infections, characterized by the sudden onset of symptoms of a relatively short duration, and ____ infections that can continue with or without symptoms for years.

acute; persistent

Viruses that specifically target and kill cancer cells are called ____ viruses

oncolytic

In acute viral infections, although the infected host cells may die, the host may survive because ______.

the host's immune system may gradually eliminate the virus

In which type of infection does the virus remain in the host for years, sometimes without symptoms?

Persistent