Viruses, Viroids, and prions

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

lytic (virulent)

without an envelope

naked

The smallest virus is approximately 10 ______ in diameter.

nanometers

Viruses that specifically target and kill cancer cells are called

oncolytic viruses

genome is injected into cell or diffuses into cell

penetration of bacterial viruses

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

specialized

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

spikes

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

temperate

act as mRNAs and can be directly translated by host cell machinery. Must encode as RNA-dependent RNA polymerase They are usually translated as a singly polyprotein, which is cleaved by host cell or viral proteases.

+ssRNA

has to encode RNA-dependent RNA polymerase enzyme but not right away

+ssRNA

our cells only deal with _____, they can't handle _____

+ssRNA, -ssRNA

must have the RNA-dependent RNA polymerase enzyme encoded and premade

-ssRNA

Characteristics that classify viruses

Genomic Structure Virus Particle Structure Presence of absence of envelope

DNA or RNA, single-stranded or double stranded

Genomic structure of viruses (used to classify)

Each virus has unique adhesion on its surface that bind to spec. cellular receptors limiting which cells can be infected many so specific they only infect a particular cell in a particular host.

Mechanism by which viruses are specific for their host cells.

Protective protein coat composed of capsomeres

Structure of viral capsid

RNA in cytoplasm, DNA in nucleus

Synthesis of animal viruses

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

Human cells are larger than viruses by which size factor?

Thousand

rapid onset and short in duration

acute

what capsid is made out of

capsomeres

infectious virus particle

virion

is an infectious agent that lacks a capsid and consists only of RNA.

viroid

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

Filamentous

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

Generalized

The study of bacteriophages has advanced much faster than investigations on animal viruses in part because ______.

It is easier to grow bacterial cells than animal cells

Which of the following about classifying viruses is FALSE?

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

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

Specialized

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

both Viroids and prions

animal viruses. outgrowth of the parent cell receives a copy of the genetic material, enlarges, and detaches.

budding

Surrounded by lipid membrane which is derived from a cellular membrane during a process called budding

enveloped

include the proteins that enable the virus to bind to host cells.

functions of viral envelope

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

Double stranded RNA viruses are treated the same way as

negative sense RNA viruses

must encode an RNA dependent RNA polymerase, which is also packaged in capsid and makes complementary mRNA from the - strand template. Resulting mRNAs usually encode a single protein each.

-ssRNA

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

virulent

Which of the following are non-cellular infectious agents?

virus, viroid's, and prions

Some carry copies of oncogenes as part of their genome, some promote oncogenes already present in host, some interfere with tumor repression, specific viruses is only ~15% of human cancers. Double-stranded DNA viruses are responsible for most virus-induced tumors in humans.

ways a cell can become cancerous

removal of capsid by cell enzymes

Uncoating of animal viruses

Which of the following statements about viruses are true?

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

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 describes the various viral parts coming together to produce virions?

assembly

in cytoplasm

assembly of bacterial viruses

spikes, capsids or envelope proteins attach to proteins or glycoproteins on cell membrane

attachment of animal viruses

proteins on tails attach to proteins on cell wall

attachment of bacteria viruses

Animal viruses ______.

can only be grown in animal cells

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

cell culture

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

cell growth

infectious virus can be detected at all times. Disease may be present or absent during extended times or may develop later. Hepatitis B.

chronic

replicase prepacked

dsRNA

Which types of viruses are released by budding?

enveloped viruses

associated with animal viruses. Some animal viruses incorporate viral genetic material into genome

latency

Infection is followed by symptomless period, then reactivation. Herpes, Shingles, Chickenpox

latent infections

Viral genome remains silent within the cell

latent state

Animal viruses can be studied by infecting ______

live animals cell or tissue culture Fertilized chicken eggs

bacteriophages . A process that kills the cell by bursting its membrane and cell wall if present

lysis

virus enters cell, viral genome is integrated into host cell genome and lies dormant until reactivation that ends in lytic infection. Integrase enzymes helps with integration of the viral genome into the host.

lysogenic

protein coat with nucleic acid inside

nucleocapsid

derived from a cellular membrane via budding

origin of viral envelope

capsid enters cell by direct penetration, fusion, or endocytosis

penetration of animal viruses

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

persistent

includes latent, chronic, and slow infections. Viruses are continually present in the host. Release via budding NOT lysis.

persistent

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

plaque assay

new viral particles are produced

productive infection

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

release

naked version: exocytosis or lysis enveloped version: budding

release of animal viruses

lysis

release of bacterial viruses

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

False

The term helical, icosahedral, and complex refer to

shapes of viruses

lipid membrane containing viral proteins

structure of viral envelope

in cytoplasm

synthesis of bacterial viruses

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

transduction

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

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

viroid

Protect nucleic acid of virus from attack by host's defensive cells. Attaches to a specific receptor site of a cell membrane.

Functions of viral capsid

Polyhedral, pleomorphic, helical

virus particle structure

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

assembly

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

Productive lytic infection Latent infection where host cell genotype is changed

none

uncoating of bacteria viruses

Which are the two major categories of viral infections?

Acute; persistent

RNA in cytoplasm, DNA in nucleus

Assembly in animal viruses

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

Lysogenic

infectious agent gradually increases over a long period of time. No significant symptoms appear during this time. Retroviruses like HIV and Prions

Slow infections

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

Transcription of viral genes Translation of viral genes Replication of viral genome

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

homologous recombination

Symptoms of acute viral diseases result from

host tissue damage Host immune response

require rapidly growing host cells.

how DNA genomes are replicated and expressed

Viruses are best described as _______.

infectious agents

An infectious agent that consists of protein and no nucleic acid is called

a prion

A prion is best described as ______.

a proteinaceous infectious agent

Oncoviruses are viruses that can ______.

cause cancer in humans

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

cytoplasmic membrane

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

associated with certain bacteriophages like lambda phage. Characterized by formation of a prophage which is a viral genome that is inserted into the genome of the host cell

lysogeny

virus enters, takes over host cell machinery, replicates and bursts the cell

lytic

proteinaceous infectious agents, linked to a number of fatal human diseases. Cellular PrP^C protein made by all mammals with helixes. Prion PrP^SC disease causing form with beta-pleated sheets.

prions

Outside living cells, viruses are

metabolically inert

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

transduction

extremely small, circular pieces of RNA that are infectious and pathogenic in plants. Similar to RNA, but lack a capsid.

viroids

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

Attachment Penetration and Uncoating Synthesis of viral proteins and replication of the genome Assembly Release