Chapter 13. Viruses, Viroids, and Prions

Match each gene type with the correct description

Proto-oncogene - stimulates cell growth Tumor suppressor gene - inhibits cell growth

Replicases are _____ polymerases

RNA-dependent RNA

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

Retrovirus

In ____ transduction, only bacterial genes adjacent to the prophase can be transferred; whereas in _______ transduction, any bacterial gene can be transferred

Specialized; generalized

In single strand (+) RNA viruses ______

The viral genome functions as mRNA and is translated

True or False: Normal prion proteins can have the same amino acid sequence as the abnormal form of the protein

True

True or false: Replication of a single stranded (-) RNA virus requires synthesis of a (+) RNA before new viral particles can be produced.

True

True or false: Tumor tissue can serve as a cell line for viral culture

True

True or false: Viruses can contain either DNA or RNA, but not both

True

This image shows the ____ stage of the lytic cycle of the T4 phage

assembly

This image shows the _____ stage of the M13 filamentous phage replication cycle

attachment

Identify all the methods by which an enveloped virus can gain entry into animal cells

b. fusion of the viral envelope and the cell membrane c. endocytosis of the virus by the host cell

Although live animals and fertilized chicken eggs have been used to cultivate animal viruses in the past, these have now been largely replaced by _____ culture

cell

Tumors are abnormal growths that result from a malfunction in the regulation of ______

cell growth

Multinucleated cells and inclusion bodies are examples of _____ effects

cytopathic

Which types of viruses are released by budding?

enveloped viruses

M13 particles are assembled during a process called ______, which the virus uses to exit the cell

extrusion

_______ phages cause productive infections that do not kill the host cell

filamentous

Replication of double-stranded DNA viruses _____

follows the central dogma of molecular biology

The molecules that viral spikes attach to on the host cell in order to gain entry are typically ______

glycoproteins

The _____ assay involves serially diluting viral samples, mixing each dilution with red blood cells, and determining the highest dilution that shows maximum clumping of the red blood cells

hemagglutination

During specialized transduction, DNA from another bacterial cell may be integrated into the recipient cell chromosome by _____ recombination

homologous

Following generalized transduction, DNA from the donor cell may be integrated into the host chromosome by _____ recombination

homologous

Following generalized transduction, DNA from the donor cell may be integrated into the recipient cell chromosome by ______ recombination

homologous

Protection of lysogens from infection by the same phage is called _____

immunity to superinfection

Through the process of phage ______, a prophage is excised and enters the lytic cycle

induction

The parameters illustrated in this figure best describe a(n) _____ infection

latent

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

lysogenic conversion

Most animal DNA viruses replicate within the host cell's

nucleus

Lysogens are protected against infection by the same phage because the phage-encoded repressor protein binds to the ____ on the incoming phage, preventing expression of the phage genes.

operator

_____ assays are routinely used to quantify phage particles in environmental samples such as sewage

plaque

To maintain the lysogenic state, a _______ protein prevents expression of the gene required for excision

repressor

A virus acquired by inhalation would be called a(n)

respiratory virus

Reassortment of gene segments that encode viral surface proteins that are 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

_____ phages have the option of entering the prophage state, while _____ phages always burst the host cell shortly after infection.

- Temperate - lytic

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

- translation of viral genes - replication of viral genome - transcription of viral genes

Which of the following occur during the synthesis stage of the T4 lytic cycle?

-synthesis of phage proteins -Degradation of bacterial DNA -Synthesis of phage DNA

Which suffix represents a viral genus?

-virus

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

DNA RNA

True or false: All virus infections can be clearly categorized as either acute or persistent

False

True or false: Most bacteria engulf bacteriophages as part of the phage replication strategy

False

Why are bacteriophages easier to study than animal viruses?

It is easier to grow the bacteriophage host cells in the lab

Rank the following by size, from smallest to largest, starting with the smallest at the top

1. Viruses 2. Bacteria 3. Human cells

The typical symptoms of cold sores can be caused by _______

- an initial infection with HSV-1 - latent HSV-1 that has reactivated

List the steps of an animal virus infection cycle in the correct order:

- attachment - penetration and uncoating - synthesis of viral proteins and replication of the genome - assembly - release

Enveloped viruses can derive their envelopes from ______

- certain host organelles - the host cytoplasmic membrane

The two categories or persistent infections are _____ and ______

- chronic - latent

Which of the following methods can be used to quantify animal viruses?

- quantal assay - plaque assay - hemagglutination - direct count

Regarding animal viruses, which of the following statements are true?

- some viruses require more than one host receptor for attachment - blocking a host receptor with a drug would prevent a virus from infecting that cell - viruses use their spikes to attach to host cell receptors

In the case of retroviruses, reverse transcriptase use a viral RNA template to synthesize DNA, which can then be _______.

- transcribed and translated to form new virions - integrated into a host cell chromosome where it remains latent

In a(n) _____ viral titer can be determined by counting clear zones in a monolayer of cells

plaque assay

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

envelope

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

lysogenic

Which of the following are the three general shapes of most viruses?

- helical - complex - icosahedral

Which of the following about classifying viruses is FALSE?

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

True or false: Viral particles can be shed from a host in feces, urine, genital secretions, blood, or mucus and saliva released from the respiratory tract during coughing or sneezing, allowing for transmission to a new host.

True

What are the two types of transduction?

generalized and specialized

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

specialized

After a virus enters a cell, the nucleic acid separates from the protein coat, a process called ____

uncoating

Which of the following cycles ends with the death (lysis) of the bacterial host cell?

Lytic

Infections that have a sudden onset of symptoms of relatively short duration are described as _____ infections

acute

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 persistant

Enveloped viruses exit host cells by _____; non-enveloped viruses are released upon ____ of the host cell

budding, apoptosis

The number of phage particles released from a host cell is called the _____ size

burst

Animal viruses ________

can only be grown in animal cells

The concentration of infectious phage particles in a sample is called the ________

titer

Phage heads that contain only bacterial DNA are called generalized _____ particles

transducing

Match the genome of each type of RNA virus with its description of function

(+) strand genome - serves as mRNA (-) strand genome - Is the complement to mRNA double-stranded genome - Consists of both a(+) and (-) strand

In double-stranded RNA viruses, the viral replicase uses the ___ strand of RNA to make ___ strands of RNA that can then be translated

(-) then (+)

Which of the following are diseases caused by prions?

- Creutzfeldt-Jakob disease - Bovine spongiform encephalopathy - Scrapie

Which of the following statements about prions are true?

- Infectious prion proteins are insoluble and aggregate in brain tissue - Infectious prion proteins can convert normal prion proteins into an abnormal form - Infectious prion proteins have a different shape from normal prion proteins

Match each tumor type to the correct statement

- Malignant - spreads to nearby tissue - Benign - does no spread to nearby tissue (fatty tissue)

True or False: Lysogen are more susceptible to reinfection by the same type of phage

False

True or false: Viroids contain a capsid but lack an envelope

False

True or false: When a bacterial culture is infected with a temperate phage, all particles of the phage will lysogenize their host

False

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

assembly

This image shows the _____ stage of the T4 phage lytic cycle

attachment - where the little bodies are crawling on the cell

A viral capsid is made up of subunits called _______

capsomeres

Tumors are abnormal growths that result from a malfunction in the regulation of _____________.

cell growth

The hepatitis B virus sometimes causes an infection that results in a continuous and low-level production of virus particles. This type of infection pattern is specifically described as a(n) _____ viral infection

chronic

If viruses are present in high enough concentrations in a sample, they can be quantified directly using a(n) ______ microscope

electron

RNA viruses have a higher mutation rate than DNA viruses because replicase lacks ______ ability

proofreading

A _____ is an animal virus genome residing silently in a host cell genome

provirus

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

reverse transcriptase

Which are the two major categories of viral infections?

- Persistent - Acute

The physical rupture of a cell is termed

- lysis

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

-Assembly -Attachment -Release -Biosynthesis of viral components -Genome entry

Circular clearings in a bacterial lawn, caused by phage-induced lysis, are called ________

plaques

In this image of a lawn of bacteria infected by a phage, the small, circular clearings are called _____

plaques

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

- Productive infection - New viral particles are produced - Latent state - Viral genome remains silent within the cell

Which of the following are viral protein components that attach to specific receptors on host cells?

- Spikes - Tail fibers

Which of the following are cytopathic effects of viruses?

- Synctia - Inclusion bodies

When cultivated in flasks, human cells from solid tissues _______

- adhere to the bottom of the surface - grow as a monolayer

Methods for cultivating animal viruses include _____

- embryonated chicken eggs - tissue culture

A non-enveloped virus can gain entry into animal cells via _____

- endocytosis of the virus by the host cell

Animal viruses can be studied by infecting _____

- fertilized chicken eggs - cell or tissue culture - live animals

Which are the two main criteria used in classifying viruses?

- genome structure - host range

In RNA viruses that have a single strand (+) RNA genome, the viral genome _____.

- is used as a template to make complementary (-) RNA strands that act as templates to produce more (+) RNA strands - can be translated to make proteins

At a minimum, all viruses are composed of ______.

- nucleic acids - proteins

Which of the following are non-cellular infectious agents?

- prions - viroids - viruses

Some viruses cause an infected cell to form a distinct region called an ______ body, which is the site of viral replication

inclusion

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

DNA ploymerase