Chapter 13 - Viruses Viroids and Prions - MIC 205A

Lysogeny is best described as ______.

integration of the viral genome into the host chromosome

Viruses that can cause cancer in humans are known as ______ viruses.

oncogenic or oncoviruses

Viruses that specifically target and kill cancer cells are called ________ viruses.

oncolytic

An infectious agent that consists of protein and no nucleic acid is called a(n) ____________

prions

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

release

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

retrovirus

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

specialized

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

temperate

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

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

- Latent infection where host cell genotype is changed - Productive lytic infection

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

Persistent or Chronic

Replicases are ______ polymerases.

RNA-dependent RNA

Human cells are larger than viruses by which size factor?

Thousand

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

cell growth

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

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

Filamentous

Which of the following about classifying viruses is FALSE?

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

Infectious agents that have a simpler structure than viruses include ______.

both viroids and prions

The smallest virus is approximately 10 ______ in diameter.

nanometers

Which of the following statements about viruses are true?

- Viruses contain RNA or DNA but not both. - The viral capsid is composed of protein.

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

- negative, -, minus, or (-) - positive, +, plus, or (+)

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

1. Attachment 2. Penetration and uncoating 3. Synthesis of viral proteins and replication of the genome 4. Assembly 5. release

A(n)________ is an infectious agent that lacks a capsid and consists only of RNA.

vivoid

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

Nucleus

_______ are viruses that are capable of infecting and selectively killing cancer cells.

Oncolytic viruses

Which of the following are non-cellular infectious agents composed of only a single-stranded RNA molecule?

Viroids

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

assembly

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

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

cytoplasmic membrane

True or false: it is easier to cultivate animal viruses than bacteriophages.

false; animal viruses need animals or animal cells for cultivation

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

plaque assay

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

replicase

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

reverse transcriptase

True or false: There is no need to classify viruses because they are not living organisms.

False

______________ phages cause productive infections that do not kill the host cell.

Filamentous

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

spikes

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

temperate

Viral infections in plants can cause diseases ______.

that are economically devastating

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 single strand (+) RNA viruses, ______.

the viral genome functions as mRNA and is translated

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

tumor

A _______ is a single virus particle.

virion

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

virion

Symptoms of acute viral diseases result from ______.

- host immune response - host tissue damage

What are the two types of transduction?

- specialized - generalized

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

Generalized

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

Generalized

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

retrovirus

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

lytic, virulent, or T4

Specialized transduction ______.

- results from errors in excision of the prophage - transfers phage DNA and adjacent host genes - produces defective phage particles

What are the two types of transduction?

- specialized - generalized

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 are non-cellular infectious agents?

- Viruses - Prions - Viroids

A bacteriophage plaque assay is designed to enumerate phage particles. Place these steps in the correct order, starting with the host cell prep at the top.

1. Regular bacterial growth 2. Dilutions of viral samples is prepared 3. Host bacteria and dilution of viral sample are mixed in liquid soft-agar 4. Mixture is poured on top of plate and allowed to harden 5. Plates are incubated overnight 6. Circular zones of clearing in bacterial growth are observed and counted.

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

1. attachment or adoption 2. genome 3. synthesis or biosynthesis 4. Release or lysis

Signs of viral infections in plants include ______.

= presence of tumors - yellowing of leaves - stunted growth

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

Assembly

Unlike animal viruses that attach to specific receptors in order to gain entry into the cell, _______________ viruses can gain entry into a cell through damage in the cell wall.

Plant

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

Plaque

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

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

Reverse transcriptase is a(n) ______ polymerase.

RNA-dependent DNA

In transduction, only bacterial genes adjacent to the prophage can be transferred.

Specialized

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

homologous recombination

Viruses are best described as _______.

infectious agents

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

Specialized

True or false: Double-stranded RNA viruses carry their own replicase because the host cell cannot translate double-stranded RNA.

True

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

prophage

A prion is best described as ______.

a proteinaceous infectious agent

Animal viruses ______.

can only be grown in animal cells

Oncoviruses are viruses that can ______.

cause cancer in humans

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

nucleus

Plant viruses initially gain entry to host cells by ______.

passing through wounds in the host cell wall

Which types of viruses are released by budding?

Enveloped viruses

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

Which are the two major categories of viral infections?

- Persistent - Acute

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

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

Animal viruses can be studied by infecting ______.

- fertilized chicken cells - cell or tissue cultures - live animals

Bacteriophages play a role in two types of transduction____________ and ______________.

- generalized - specialized

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

Electron

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

virulent