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