Micro Exam 1 ch. 6

three methods used by viruses to gain entry into host cells.

1. injection of viral nucleic acid into the cell 2. fusion of the viral envelope with host cell membrane 3. endocytosis of the virus into the cell

Which is NOT true about lysogenic bacteria?

They would normally stop dividing.

Many RNA viruses must ______ to replicate their genomes.

carry their own enzymes

Examples of viral ligands on bacterial and archaeal viruses include

claw-like structures beard-like fiber clusters tail fibers

Which of the following best describes the normal mechanism of RNA silencing in eukaryotic cells?

detection and degradation of dsRNA

In contrast to viral genomic DNA, which may be dsDNA, ssDNA, dsRNA, or ssRNA, cellular genomes are always _____

dsDNA

The second step of the viral life cycle is ____.

entry

The outer lipid membranous layer found surrounding some viruses is called the

envelope

What viral structure is different between these two viruses?

envelope

The portion of the illustrated bacteriophage life cycle labeled A is termed _____.

lytic

Normal cellular genes that result in cancer when mutated are called proto-

oncogenes

Viroids cause disease in what type of host?

plants

Prions are composed of _____.

protein only

During T4 bacteriophage release, holin will ____.

put holes in the cell membrane

What term describes the host cell component that a virus will bind for attachment?

receptor

Once a virus enters the cytoplasm of a host cell, it begins to _____.

replicate its genome

Which of the following best describes a virus?

An acellular infectious agent that can only replicate within a host cell.

What types of viruses can use endocytosis as a means of viral entry?

Both enveloped and naked viruses

What name is given to a viral capsid that is shaped like a hollow tube with protein walls?

Helical

What name is given to a viral capsid that is composed of 20 equilateral triangular protomer faces?

Icosahedral

Most viruses will leave a host cell by bursting the cell, a process called _______________ , or by pushing through the cell membrane while taking some of that membrane with it, a process called ___________.

Lysis, lytic, or lysing budding

Which of the following describes the role of tumor suppressor proteins?

Most regulate cell division

Viroids are infectious agents that consist of _____.

RNA only

Because their host cells typically lack the appropriate enzymes, which type of viruses always encode the enzymes needed to copy their genome?

RNA viruses

Which two of the following are tumor suppressor proteins?

Rb and p53

Which two of the following are examples of lysogenic conversion?

Salmonella producing novel lipopolysaccharides Corynebacterium diphtheria causing diphtheria

What viral life cycle step generally occurs after the virus has uncoated?

Synthesis

Which of the following best defines what "infectious dose (ID50)" means?

The dilution that contains enough virions to infect 50% of the host organisms

Which of the following best defines what "lethal dose (LD50)" means?

The dilution that contains enough virions to kill 50% of the host organisms

The study of viruses is termed

Virology

Fertilized chicken eggs are a good medium to grow _____

animal viruses

This image depicts which stage of T4 bacteriophage replication?

assembly

Which two stages of viral replication occur after viral synthesis?

assembly and released

The function of viral spike proteins is to ____.

attach to a host cell surface

The energy for viral replication, gene expression, and nucleocapsid assembly comes from _____.

host ATP

RNA viruses always encode the enzymes needed to replicate their genomes because

host cells typically do not have ways to make RNA from RNA templates.

Viral specificity for a host cell type is dependent on ____.

host receptor and viral ligand

Budding is best described as

how enveloped viruses acquire their membranes

During T4 bacteriophage release, lysozyme will ____.

hydrolyze the peptidoglycan cell wall

Oncoviruses are known for their ability to _______.

induce cancer

What name is given to the process that leads a lysogenic virus to transition to the lytic cycle?

induction

When a change in conditions causes a prophage to begin synthesizing and assembling new virions, this is called ___________.

induction

Which two of the following techniques allow the cultivation of animal viruses?

inoculating tissue culture with animal cells inoculating fertilized chicken eggs

An icosahedral capsid _____.

is a regular polyhedron

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

latent period rise period plateau

A bacterial plaque assay requires the use of a ____.

lawn of cells

The dose of virions needed to kill 50% of host organisms is called the ________ dose.

lethal

What is the generalized term used to describe the viral component that is used to bind to a host cell for attachment?

ligand

A viral envelope is composed of primarily ____.

lipids

Bacteria infected by temperate phages are called ______ bacteria.

lysogenic

The portion of the illustrated bacteriophage life cycle labeled B is termed _____.

lysogenic

_____________ ______________ is when a temperate phage causes a change to the phenotype of an infected bacterial cell.

lysogenic conversion

When a temperate phage integrates its genome into a host genome, the relationship between the phage and the host is termed

lysogeny

Which two of these eukaryotic cell endocytic pathways are used by some virions to enter the cell?

macropinocytosis clathrin-dependent endocytosis

The image shows one mechanism of animal virus entry to the host cell, specifically _____.

membrane fusion

Cells from cancerous tumors actively spread throughout the body in a process known as _____.

metastasis

Which three of the following are larger than the average virus? mitochondrion animal cell fungal cell oxygen atom hemoglobin

mitochondrion animal cell fungal cell

Viruses that lack a viral envelope are often called ____.

naked

A tumor is a growth or lump of tissue resulting from ____________, which means unregulated abnormal new cell growth and reproduction of a similar cell type.

neoplasia

What effect would lysozyme have on a eukaryotic cell?

none, Lysozyme hydrolyzes peptidoglycan cell walls.

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

Which two of the following components make up a viral nucleocapsid? protein coat envelope cell wall peptidoglycan nucleic acid

protein coat and nucleic acid

The main difference between proto-oncogenes and tumor suppressor genes is that

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

What name is given to the repeating protein subunits that compose viral capsids?

protomer

Enveloped viruses gain their envelope from ____.

the host cell membrane

Which of the following best describes viral tropism?

the specific cell type that a virus can infect

Some viruses infect specific tissue types but not others. This is called ____.

tropism

True or false: Viruses that have RNA genomes must carry enzymes in their virion to aid in replication once in a host cell.

true

Which two of the following viral activities occurs during "viral entry"?

uncoating and penetration

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

Bacteriophages that always proceed to lyse the infected cell are called __________ phage.

virulent

An acellular infectious agent that must replicate within a host cell is a(n)

virus

In the context of virus replication, fusion with the host cell membrane, injection of nucleic acid, and endocytosis are the three modes of _____.

virus entry into host cells

The image shows the result of mixing bacteriophage T4 with E. coli and adding to a solid medium. The plaques, indicated by the arrow, represent _____.

viruses and lysed bacterial cells

Viral genes are classified as early, middle, or late based on _____.

when they are expressed during the infection

Which of these viruses is considered naked?

A

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.

The image shows typical results of a one-step growth curve. Match the letter representing each component shown in the graph with the best description of what's happening at that time.

A: time during which host cells contain no complete virions B: time when infective virions are present but none are released. C: time when infective virions are released into the median D: Number of virions produced per infected cell

Select the two direct methods for counting viruses.

electron microscopy immuno-fluorescence microscopy

The image shows one mechanism of animal virus entry to the host cell, specifically _____.

endocytosis

Viruses with a lipid membrane are often called ____.

enveloped

Describes virus (c)?

enveloped helical virus with spikes

Which of the following best describes virus (b)?

enveloped icosahedral virus with spikes

True or false: The cell membrane is the only host cell structure from which enveloped viruses obtain their envelope.

false, Actually several viruses get their envelopes from the ER and Golgi.

Select the three methods that would most likely be successful in cultivating (growing) a plant virus.

- grafting part of an infected plant onto a healthy plant - inoculating a culture of protoplasts - rubbing a mixture of virus and an abrasive on whole plants

The first step in a typical viral life cycle is

attachment

Which three of the following statements about prion diseases in humans and other animals are correct?

- there are no cures or effective treatments. - They cause brain degeneration. - They are uniformly fatal

The RNA of viroids encodes how many gene products?

0

Arrange the steps in Delbruck and Ellis' one-step growth experiment in chronological order, with the earliest step at the top. - Remove samples over time to determine the number of infectious phage particles - Mix T4 phage with E. coli bacteria - Wait a short period to allow viral attachment - dilute the culture so visions don't infect new cells, then incubate

1. Mix T4 phage with E. coli bacteria 2. Wait a short period to allow viral attachment 3. dilute the culture so visions don't infect new cells, then incubate 4. Remove samples over time to determine the number of infectious phage particles

Rank the following from smallest to largest. a typical virus a typical bacterial cell a typical eukaryotic cell a typical protein

1. a typical protein 2. a typical virus 3. a typical bacterial cell 4. a typical eukaryotic cell

Arrange the steps in RNA silencing by viroids according to the order in which they occur, with the earliest event at the top.

1. dsRNA is cut into small fragments 2. Viroids hybridize to specific host mRNA molecules 3. Normal host cell functions are compromised, cause disease

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

DNA

Because viroids code for no enzymes of their own, it is believed that they are replicated by a normal host cell enzyme called _____.

DNA-dependent RNA polymerase

Which of the following viral structures comes principally from the host cell?

Envelope

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.

If a tumor cells remain in place to form a compact mass, the tumor is said to be _____.

benign

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

Select the two most common forms of viral release.

budding and lysis

The protein coat that surrounds the viral nucleic acid is called the

capsid

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

Virus (e) in this image has a capsid with which sort of viral symmetry?

complex

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

cytopathic

The main difference between virulent phage and temperate phage is that virulent phage _____.

only have a lytic cycle

The virus-associated pyramids found in Sulfolobus cells infected with STIV function to release virions by

opening like flower petals

Inoculating protoplasts, tissue cultures, or whole organisms, or grafting a diseased part onto a healthy organism, are all methods used to cultivate _____ viruses.

plant

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 ___________.

plaque

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

Select the two indirect methods for counting viruses.

plaque assay hemagglutination assay

Select the four cellular structures that can be the source of viral envelopes.

plasma membrane endoplasmic reticulum Golgi apparatus nuclear membrane

Viruses that have a somewhat variable shape due to the viral envelope are called ____.

pleomorphic

Infectious agents composed entirely of protein are called _____.

prions

Kuru, Creutzfeldt-Jakob disease, fatal familial insomnia, and Gerstmann-Strassler-Scheinker syndrome are human disease caused by _____.

prions

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 are correct descriptions of viroid structure?

relatively short; about 250 to 400 nucleotides long circular ssRNA

The last step in the replication cycle of a virus is generally called

release

The virus-associated pyramids found in Sulfolobus cells infected with STIV function in which stage of the viral life cycle?

release

Which stage of virus replication is shown in the image?

release

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

Viral genomes composed of multiple pieces of RNA are called ________ genomes.

segmented

The viral-encoded proteins that project from a viral envelope surface are called ____.

spike proteins

A single virus could have which genomes?

ssDNA dsDNA dsRNA ssRNA

This picture represents which of the following macromolecules?

ssRNA

Early proteins in a viral life cycle function to _____.

take over the host cell

Examples of viral receptors on bacterial cells include

teichoic acids flagella cell wall polysaccharides

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