Chapter 6: Viruses and Other Acellular Infectious Agents

Which type of genome would seem simplest to replicate in a host cell?

DNA (it is the natural genomic material of all life)

What is the name of the repeating protein subunits composing viral capsids?

Protomer

____ viruses always encode the enzymes needed to copy their genome because the host cells usually lack the needed enzymes to do it.

RNA

Viral proteins that can bind to tumor suppressor proteins would have what 2 likely targets?

Rb & p53

What are the viral activities during "viral entry"?

penetration and uncoating

Viral envelopes can often give a collection of identical viral species different shapes. What is this called?

pleomorphic

What host cell structures can enveloped viruses obtain their envelope?

ER, Golgi, nuclear membrane, and plasma membrane

What is the name for a viral capsid composed of 20 equilateral triangular protomer faces?

Icosahedral

What are the 3 ways viruses use to gain entry into host cells?

injection of viral nucleic acid, endocytosis of the virus, fusion of the viral envelope with host cell membrane.

List parts of a viral growth curve determined by one-step growth experiment by Delbruck and Ellis.

latent period, rise period, & plateau

Viruses will attach to host cells via a viral ____ and a host ____.

ligand, receptor

What is it called when a temperate phage integrates its genome into the host genome?

lysogeny

what is the 3rd step in RNA silencing by viroids?

normal host cell functions are compromised, causing disease.

What is a prophage?

nucleic acid of a temperate phage that has integrated into the host's genome or remains free in the cytoplasm

What makes up the nucleocapsid of a virus

nucleic acid, capsid, protomers

What is the burst size of the one-step growth curve?

number of virions produced per infected cell

describe this step of the one-step growth curve: burst size

number of virions produced per infected cell

What are viruses that can cause cancers?

oncoviruses

viruses that tend to cause cancer are called....

oncoviruses

What is the main difference between proto-oncogenes and tumor suppressor genes?

proteins encoded by proto-oncogenes stimulate cell division; proteins encoded by tumor suppressor genes inhibit cell division.

What is it called when a preexisting gene is mutated by a virus that results in cancer?

proto-oncogenes

What are the components of the nucleocapsid of a virus?

protomers, capsid, nucleic acid

Either 5 or 6 ______ usually combine to make each _____ in the icosahedral capsids of viruses.

protomers, capsomers

What is a plaque assay?

quantitative method used to count viruses by numbering the clear spots on a cell lawn.

CD4 & CCR5 are host cell _____ which are targets for which virus?

receptors, HIV

What is the difference between satellite viruses and nucleic acids?

satellite viruses composed of nucleic acid AND protein while satellite nucleic acids are composed of nucleic acids only

Viral genomes composed of multiple pieces of RNA or DNA are called ____ genomes

segmented

the following are listed how regarding size: protein, virus, bacterial cell, eukaryotic cell

smallest to largest

Viruses that infect plant cells require what in order to infect the cell?

something to damage the cell wall

What kind of genomes do most plant viruses have?

ssRNA

What step of viral entry occurs after the virus has "uncoated".

synthesis

What is a plaque-forming unit or PFU?

the dilution of viruses that generates the number of plaque seen in a plaque assay.

What is LD50

the dose of virions needed to kill 50% of host organisms

What is viral budding?

the process of an enveloped virus leaving the cell.

What is the capsid?

the protein coat that surrounds the viral nucleic acid

What are peplomers or spike proteins?

the proteins that extend out from the viral envelope used to bind to host cell

One clear distinction between cellular organisms and viruses is what?

their genomes: cellular genomes are always double-stranded DNA

What is a temperate phage?

these have 2 options: act like a virulent phage or they can remain within the host without destroying it. lysogenic.

describe this step of the one-step growth curve: latent period

time after infection where an increasing number of infective virions are present but none are released

What is the latent period of the one-step growth curve?

time after infection where an increasing number of infective virions are present but none are released.

describe this step of the one-step growth curve: rise period

time when infective virions are being released into the medium

What can influence viral morphology?

type of capsid symmetry, presence or absence of an envelope

What happens during "viral entry"?

uncoating & penetration

What is neoplasia?

unregulated abnormal new cell growth and reproduction of a similar cell type, usually results in a tumor.

What is the first step in RNA silencing by viroids?

viroids hybridize to specific host mRNA molecules

What is the rise period of the one-step growth curve?

when infective virions are released into the medium

What is multiplicity of infection or MOI?

when there are many different infectious agents, a temperate bacteriophage can inhibit infection of the same cell by other virions.

What is a satellite?

-a disease agent that can either have a RNA or DNA genome -must have helper virus to facilitate replication

What can the size of a viral genome be?

4000 to 1.2 billion nucleotides long

When a virus can infect the nasopharynx, gut, & anterior horn cells of the spinal cord, but NOT other is called?

Tropism

What is directly involved with viral attachment?

Viral ligand & host receptor

Most bacteriophages are either ____ or ____.

Virulent or temperate

When does lysogenic conversion occur?

When a phage causes a new phenotype to be expressed/integrated in an infected bacterial cell.

What is a lysogenic bacteria

a bacteria infected by temperate phages

What is a virulent phage?

a bacteriophage that immediately begins to multiply upon entering its bacterial host, followed by release from the host by lysis.

What is a virion?

a complete virus particle

describe the poxviruses.

among largest of animal viruses, can be seen with light microscope, complex internal structure with ovoid- to brick-shaped exterior, vaccinia virus morphology

What is Neuraminidase?

an influenza virus protein that allows mature virons to leave infected cells

What is Hemagglutinin?

an influenza virus protein that facilitates viral attachment to host cells

What is it called when a tumor has reverted to a more primitive or less differentiated state?

anaplasia

What two stages of viral replication occur after viral synthesis?

assembly and release

What is the first step of a typical viral life cycle?

attachment

starting with "floating around", give the order for a typical viral life cycle.

attachment, entry, synthesis, self-assembly, & release

Virus that infect bacterial cells are generally called ____.

bacteriophages or phages

What are the most common forms of viral release?

budding and lysis

What is the difference between the envelope and the capsid?

capsid is composed of protein, envelope is composed of lipids

viruses that show both icosahedral and helical symmetry have what type of symmetry?

complex

The T4 phage has what kind of viral symmetry?

complex or binal

Lysogenic bacteria usually _____ dividing.

continue

Virally infected eukaryotic cells often show microscopic or macroscopic abnormalities that are generally called ____ effects.

cytopathic

What is a good definition of cytopathic effects caused by a viral infection of eukaryotic cells?

degenerative changes or abnormalities in infected cells.

During T4 bacteriophage release, lysozyme will ____.

degrade the peptidoglycan wall

What is the 2nd step in RNA silencing by viroids?

destruction of viroid-host hybrid dsRNA molecule

What is dsDNA

double-stranded DNA

most bacterial viruses have what kind of genomes?

dsDNA

Explain the events of an enveloped virus' entry into host cell in chronological order

envelope glycoproteins interact with host membrane proteins, both membranes fuse, proteinaceous fusion pore, synthesizing viral mRNA

Which viruses can use endocytosis as a means of viral entry?

enveloped and naked viruses

What are the three modes of virus entry into host cells in context of virus replication?

fusion, injection of nucleic acid, & endocytosis

What are the 2 INDIRECT methods for counting viruses?

hemagglutination assay, plaque assay

Protomers which combine as groups of six to make capsomers are called what?

hexons

If "holin" were added to a bacterial cell, what is expected to happen?

holes forming in the cell membrane

What type of viral counting method is hemagglutination assay?

indirect

Oncoviruses are known for their ability to ____.

induce cancer

What is it called when changes in conditions cause a prophage to begin synthesizing & assembling new virions?

induction

What is the ID50?

infectious dose that causes 50% of host organisms to become infected

What is the eclipse of the one-step growth curve?

initial portion of latent period when host cells contain no complete virions

describe this step of the one-step growth curve: eclipse

initial portion of the latent period during which host cells contain no complete virions

What are the methods used by viruses to get into host cells?

injection of nucleic acid, endocytosis into cell, fusion of viral envelope with host cell membrane