microbio ch 6 smartbook

Arrange the steps in Delbruck and Ellis' one-step growth experiment in chronological order, with the earliest step at the top.

1.Mix T4 phage with E. coli bacteria2.Wait a short period to allow viral attachment3.Dilute the culture so virions don't infect new cells, then incubate4.Remove samples over time to determine the number of infectious phage particles

Which of the following best defines a virulent phage?

A virus that always progresses to lysis of the host cell

Which of the following best defines a temperate phage?

A virus that can integrate its genome into the host genome.

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

Both enveloped and naked viruses

Which of the following statements about lysogenic bacteria is false?

Lysogens normally stop dividing.

Viroids are infectious agents that consist of ___

RNA only

Which of the following best defines a plaque-forming unit (PFU)?

The number of virions that generates a single plaque

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

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

Which statement regarding viral assembly is false?

Viral assembly of the protein capsid around the genome occurs simply and without energy.

The study of viruses is termed ______

Virology

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

Which two of the following are correct descriptions of viroid structure?

circular ssRNA relatively short; about 250 to 430 nucleotides long

The normal PrPC protein converts to the abnormal PrPSC form by ___

contact between the two molecules

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

Arrange the parts of a viral growth curve determined by the one-step growth experiment performed by Delbruck and Ellis. The beginning of the viral growth curve should be at the top.

eclipse, latent period, rise period, plateau

The second step of the viral life cycle is ______

entry

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

envelope

Select three human diseases that are known to be caused by prions

fatal familial insomnia Creutzfeldt-Jakob disease kuru

Select the three methods used by animal viruses to gain entry to host cells.

fusion of the viral envelope with host cell membrane direct transfer of viral nucleic acid into the cell endocytosis of the virus into the cell

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

host ATP

Viral specificity for a host cell type is dependent on ______

host receptor, viral ligand

Budding is best described as ____

how enveloped viruses acquire their membranes

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, it is called ___

induction

A bacterial plaque assay requires the use of a ___

lawn of cells

What is the general term used to describe the viral component that binds 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 relationship between a temperate phage and the host cell is called ___

lysogeny

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

lysogeny

Bacteriophages that always proceed to lyse the infected cell are called ____ phages

lytic

Which two mechanisms are used by some virions to enter an animal cell?

macropinocytosis endocytosis

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 image shows typical results of what type of demonstration?

one-step growth curve with bacteriophage

The main difference between virulent phages and temperate phages is that virulent phages ___

only have a lytic cycle

Proteins synthesized by a virus are classified as structural or nonstructural. A nonstructural protein ____

participates in the viral life cycle but is not a part of the mature virion

Viroids cause disease in what type of host?

plants

Viruses can be quantified using a lawn of cells and counting the number of clear spots where the cells were lysed by viruses. This type of assay is called a(n) ___ assay

plaque

The image shows the result of mixing bacteriophage T4 with E. coli and adding to a solid medium. The visible holes are called ___

plaques

Infectious agents composed entirely of protein are called ___

prions

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

prions

A host cell that contains a ____, the genome of a temperate phage, can divide many times.

prophage

The genome 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

A virus will attach to a host cell via a viral ligand and a host _____

receptor

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

receptor

Which two stages of viral replication occur after viral synthesis?

release, assembly

Once a virus enters the cytoplasm of a host cell, which step would occur next? Multiple choice question.

replication of the viral 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

This picture represents which of the following macromolecules?

ssRNA

Which of the following could be the genome of a single virus?

ssRNA dsDNA ssDNA dsRNA

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

synthesis

Bacteriophages that can integrate their genome into the host genome are called ___ phages

temperate

Which of the following describes a bacteriophage that may either lyse its host cell or remain within the cell without lysing it?

temperate

Which type of viral genome uses only host enzymes to replicate?

DNA

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 medium d - number of virions produced per infected cell

Two important characteristics of PrPSC that promote pathogenesis are its ______ and its ______

aggregation stability

The viral life cycle begins when the virus and host first meet, in a step termed _____

attachment

Proteins synthesized by a virus are classified as structural or nonstructural. A structural protein _____

becomes a part of the mature virion

All known prion diseases cause degeneration of what tissue?

brain

The specific process of an enveloped virus leaving the cell is called _____

budding

Which of the following best describes viral tropism?

the specific viral type that a virus can infect

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

tropism

Which two of the following events occur during viral entry?

uncoating, penetration

The results of virus titration using a plaque-forming assay are normally expressed in PFUs, or plaque-forming ___

units

Which two of the following have direct involvement with viral attachment?

viral ligand, host receptor

Viral specificity for a host cell type is dependent on _____

viral ligand, vira receptor

A complete virus particle is called a(n)

virion

A mature virus particle assembled from all of its components is referred to as a _____

virion

An infectious agent composed of only RNA is called a(n) ___

viroid

In the context of virus replication, fusion with the host cell membrane, direct transfer 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