Microbio HW 4
Which of the following best defines a plaque-forming unit (PFU)?
A number of virions that generates a single plaque
Which of the following best defines a virulent phage?
A virus that always progresses to lysis of the infected cell
Which of the following best defines a temperate phage?
A virus that can integrate its genome into the host genome.
Viroids are infectious agents that consist of _____.
RNA only
Which of the following best defines what "lethal dose (LD50)" means?
The dilution that contains enough virions to kill 50% of the host organisms
Which is NOT true about lysogenic bacteria? They can reproduce normally. When they reproduce, they also copy the viral DNA. They would normally stop dividing. They could become pathogenic.
They would normally stop dividing.
Which two of the following viral activities occurs during "viral entry"?
Uncoating Penetration
The best definition of cytopathic effects caused by a viral infection of eukaryotic cells is
changes or abnormalities in infected cells that are distinct from lysis
Virally infected eukaryotic cells often show microscopic or macroscopic abnormalities that are generally called __________ effects.
cytopathic
In contrast to viral genomic DNA, which may be dsDNA, ssDNA, dsRNA, or ssRNA, cellular genomes are always _____
dsDNA
A single virus could have which of the following genomes?
dsRNA ssDNA dsDNA ssRNA
The second step of the viral life cycle is ____.
entry
The outer lipid membranous layer found surrounding some viruses is called the
envelope
Which of the following viral structures comes principally from the host cell?
envelope
Viruses with a lipid membrane are often called ____.
enveloped
The energy for viral replication, gene expression, and nucleocapsid assembly comes from _____
host ATP
Budding is best described as
how enveloped viruses acquire their membranes
What name is given to a viral capsid that is composed of 20 equilateral triangular protomer faces?
icosahedral
The dose of virions needed to infect 50% of host organisms is called the
id50 dose
Because it measures an effect of a virus, rather than actually counting virions, a hemagglutination assay is considered to be _____.
indirect
An icosahedral capsid ________
is a regular polyhedron
A helical capsid _____.
is shaped like a hollow tube with protein walls
A bacterial plaque assay requires the use of a ____.
lawn of cells
A viral envelope is composed of primarily ____.
lipids
Select the two most common forms of viral release.
lysis budding
Bacteria infected by temperate phages are called ______ bacteria.
lysogenic
The relationship between a temperate phage and the host cell is called ____.
lysogeny
Viruses that lack a viral envelope are often called ____.
naked
A tumor is a growth or lump of tissue resulting ________, which means unregulated abnormal new cell growth and reproduction of a similar cell type.
neoplasia
The simplest viruses consist of nucleic acid surrounded by a protein coat. This composite structure of viral nucleic acid and protein is called a ______.
nucleocapsid
The main difference between virulent phage and temperate phage is that virulent phage _____.
only have a lytic cycle
Viruses can be quantified using a lawn of cells and counting the number of "clear spots" where the cells were killed by viruses. This sort of assay is called ____________ assay.
plaque
One method of counting temperate viruses involves mixing the virus and susceptible cells on top of a solid medium. As each virus begins lysing more and more cells, holes can be visualized on top of the medium. The virus-induced holes are specifically called__________
plaques
A host cell that contains a _____________, the nucleic acid of a temperate phage, can divide many times.
prophage
The nucleic acid of a temperate phage that is either integrated into the host cell's genome, or remains free in the cytoplasm, is called a _____.
prophage
Which two of the following components make up a viral nucleocapsid?
protein coat nucleic acid
Prions are composed of _____.
protein only
Virus will attach to host cells via a viral ligand and a host
receptor
What term describes the host cell component that a virus will bind for attachment?
recptor
The last step in the replication cycle of a virus is generally called
release
Which stage of virus replication is shown in the image?
release
Which two stages of viral replication occur after viral synthesis?
release assembly
Once a virus enters the cytoplasm of a host cell, it begins to _____.
replicate its genome
A(n) __________ is a disease agent that can either have a RNA or DNA genome and must have a helper virus to facilitate replication.
satellite
Which of the following may be composed of RNA or DNA, encode one or more proteins, and must have a "helper" virus to replicate?
satellites
The viral-encoded proteins that project from a viral envelope surface are called ____.
spike proteins
Which of the following viral structures is principally involved in attaching to host cells?
spike proteins
What viral life cycle step generally occurs after the virus has uncoated?
synthesis
Which of the following describe a bacteriophage that may lyse its host cell, or remain within the cell without lysing it?
temperate
Bacteriophages that can integrate their genome into the host genome are called _________ phage.
temperate or lysogenic
Enveloped viruses gain their envelope from ____.
the host cell membrane
Virus (e) in this image has a capsid with which sort of viral symmetry?
Complex
Which type of genome would seem simplest to replicate in a host cell?
DNA
This image depicts which stage of T4 bacteriophage replication?
assembly
The function of viral spike proteins is to ____.
attach to a host cell surface
The first step in a typical viral life cycle is __________
attachment
When performing a viral plaque-forming assay and using the terminology "bacterial lawn", the word "lawn" refers to
bacterial cells virtually side-by-side, covering an agar plate.
Viral symmetry that is both icosahedral and helical and possibly other symmetry is collectively referred to as ____ symmetry
binal
Certain viruses can be counted using a hemagglutination assay, but this only works it the virus _____.
binds to red blood cells
The specific process of an enveloped virus leaving the cell is called
budding
The protein coat that surrounds the viral nucleic acid is called the _______
capsid
Which of the following viral structures is composed of just the protein that surrounds the nucleic acid?
capsid
The results of virus titration using a plaque-forming assay are normally expressed in PFUs, or plaque-forming ________
units
Spikes, or peplomers, are _____.
virally-encoded proteins that project from the envelope surface
A complete virus particle is referred to as a ____.
virion
An infectious agent composed of only RNA is called a(n)
viroid
Which of the following is the study of viruses?
virology
Bacteriophages that always proceed to lyse the infected cell are called ___________ phage.
virulent