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