Lecture 11
The viral proteins that stick out from either the lipid bilayer of enveloped viruses or the capsid of non-enveloped viruses, and attach to host cells, are ______.
Spikes
How is a latent infection different from a chronic infection?
- latent infection: symptomless period followed by reactivation of the virus with accompanying symptoms. (DNA or RNA viruses)- chronic infection: infectious virus can be demonstrated at all times. Disease symptoms may be present or absent during an extended period of time or may develop late.
Viral genomes can be ______.
either single-stranded or double-stranded
In ______-strand RNA viral genomes, the genome functions as an mRNA molecule
+ (Reason: Positive sense means that the RNA can be immediately translated)
Blank 1 phages cause productive infections that do not kill the host cell.
Blank 1: Filamentous, M13, Temperate, or Lysogenic
Which types of viruses are released by budding?
Enveloped viruses
Which of the following describe a type of relationship that bacteriophages can have with their host?
Productive lytic infection Latent infection where host cell genotype is changed
The binding of a bacteriophage surface protein to a host cell receptor is called ______.
attachment
In a lysogenic infection, the phage DNA that is incorporated into the bacterial host genome is called a ______.
prophage
Viruses that have an RNA genome and use reverse transcriptase to synthesize a DNA copy of that genome are called _____
retroviruses
Reverse transcriptase is a(n) ______ polymerase.
RNA-dependent DNA
Replicases are ______ polymerases.
RNA-dependent RNA
Which of the following are non-cellular infectious agents?
Viroids Viruses Prions
When two different strains of a segmented virus enter the same cell, reassortment of the gene segments can occur, resulting in _____
antigenic shift
The process by which a virus is taken up by a host cell as a result of the host cell's cytoplasmic membrane surrounding the virion to form a vesicle is called ______.
endocytosis
In the case of animal viruses, the molecules that viral spikes attach to on the host cell in order to gain entry are typically ______.
glycoproteins
Symptoms of acute viral diseases result from _____
host tissue damage host immune response
Viruses are best described as ____
infectious agents
During the process that leads to a lysogenic infection, which of the following inserts the phage DNA into a bacterial chromosome?
integrase
The study of bacteriophages has advanced much faster than investigations on animal viruses in part because ______.
it is easier to grow bacterial cells than animal cells in the lab
The smallest virus is approximately 10 ______ in diameter.
nanometers
Most animal DNA viruses replicate within the host cell's ______.
nucleus
In acute viral infections, although the infected host cells may die, the host may survive because ______.
the host's immune system may gradually eliminate the virus
A complete viral particle, which typically consists of nucleic acid surrounded by a protein coat, is called a(n)
virion
An infectious agent that consists of protein and no nucleic acid is called a(n) Blank 1
Blank 1: prion
Bacteriophages that can enter into a lytic cycle or a lysogenic cycle are called Blank 1 phages.
Blank 1: temperate
How does a temperate phage differ from a lytic phage?
Temperate phage: phage that can multiple in either the lytic or latent cycle. Lytic phage: phage that can only multiple in the lytic cycle and kill the cell by lysis at the end of the cycle.
Which of the following statements about viruses are true?
The viral capsid is composed of protein. Viruses contain RNA or DNA but not both.
Some lysogenic phages can increase the pathogenicity of their bacterial host
True (Reason: Temperate phages are associated with lysogenic conversion, in which phage toxins increase the pathogenicity of the host.)
Lysogeny is best described as ______.
integration of the viral genome into the host chromosome
The stage of viral multiplication at which budding occurs is ______.
release
In a lysogenic infection, ______.
the bacteriophage DNA integrates into the host chromosome
In animals, replication of most DNA viruses occurs within the host cell's Blank 1
Blank 1: nucleus
There is no need to classify viruses because they are not living organisms.
False (Reason: Although viruses are not living, classification is still important for identification and study.)
Lysogens are more susceptible to reinfection by the same type of phage.
False (Reason: Lysogens are immune to superinfection.)
DNA viruses can only replicate when the host cell is replicating its own genome.
False (Reason: Many DNA viruses encode their own DNA polymerase and can replicate even if the host cell is not replicating)
How does bacteriophage nucleic acid enter the host cell?
Injection
In which type of infection does the virus remain in the host for years, sometimes without symptoms?
Persistent
What is the difference between a productive and latent infection?
Productive infection (new viral particles are produced) vs. latent infection (viral genome remains silent within the cell but is replicated with the host cell genome)
Match each possible outcome of phage replication with the correct definition.
Productive infection=> New viral particles are produced Latent state => Viral genome remains silent within the cell
During the Blank 1 or maturation step in viral multiplication, capsids and genetic material are packaged into
Blank 1: assembly
Mutations in the influenza virus genome can result in minor changes in key viral surface proteins. This type of variation is called antigenic Blank 1.
Blank 1: drift
The nucleocapsid is composed of ______.
DNA or RNA, and protein
Which are the two major categories of viral infections?
Persistent Acute
Replication of single-stranded DNA viruses is quite similar to that of double-stranded DNA viruses, except that ______.
a complement to the single-stranded DNA molecule must be synthesized
This image shows the ______ stage of the T4 phage lytic cycle.
attachment
The replication scheme of double-stranded DNA viruses ______.
follows the central dogma of molecular biology
When an enveloped virus gains entry to an animal cell by fusion, the virus envelope fuses with the ______.
cytoplasmic membrane
In this figure, the ______ stage of the T4 phage lytic cycle is shown.
genome entry
All of the following are required for synthesis of new virus particles in a host cell EXCEPT ______.
homologous recombination
A ______ phage can either cause a lytic infection or can incorporate its DNA into the host genome as a prophage.
temperate
Bacteriophages that exit the host cell at the end of an infection by lysing it are called _______ phages.
virulent
This figure highlights a stage of the T4 phage lytic cycle known as _______.
synthesis
Which of the following are non-cellular infectious agents composed of only a single-stranded RNA molecule?
Viroids
Describe the general structure of naked and enveloped viral particles.
Naked viral particles (do not have the envelope of outer lipid bilayer) vs. Enveloped viral particles (has outer layer lipid bilayer)
What would be the consequence if a temperate phage lost the ability to synthesize a repressor?
Since a repressor binds to a viral operator that controls transcription of the integrated genes required for excision, the inability to synthesize a repressor will result in the synthesis of an enzyme (an excisase) that removes the viral DNA from the bacterial chromosome. A productive infection with lysis will result in vision release.
The major categories of animal viral infections are Blank 1 infections, characterized by the sudden onset of symptoms of a relatively short duration, and Blank 2 infections that can continue with or without symptoms for years.
Blank 1: acute Blank 2: persistent
Some pathogenic bacteria produce toxins that are encoded on prophage DNA, and these are examples of Blank 1 conversion.
Blank 1: lysogenic
HIV is described as a Blank 1 because it uses reverse transcriptase to make a DNA copy from its RNA genome.
Blank 1: retrovirus
The virally encoded polymerase needed for replication of RNA viruses is called a Blank 1
Blank 1: replicase
Which groups of viruses need to carry their own polymerase within the virion? Why?
Negative as RNA because they don't code for replicase. Replicate is needed so RNA can be transcribed to a +ve strand b4 transcription.
Blank 1 infections remain for years, or even the lifetime of the host, sometimes without any symptoms.
Blank 1: Persistent or Chronic
Infection of bacteria by Blank 1 phages always ends with the lysis of the host cell.
Blank 1: lytic, virulent, or T4
Why are phages important?
Bacteriophages (BPs) are viruses that can infect and kill bacteria without any negative effect on human or animal cells. For this reason, it is supposed that they can be used, alone or in combination with antibiotics, to treat bacterial infections.
Naked viruses do not have an outer lipid bilayer. These viruses are called Blank 1 Blank 2 viruses.
Blank 1: non Blank 2: enveloped
At a minimum, all viruses are composed of ______.
nucleic acids (Reason: All viruses have a type of nucleic acid as the heritable material for their replication.) and proteins (Reason: All viruses will have a capsid, which is composed of proteins, that surrounds their nucleic acids.)
Many animal viruses have proteins called Blank 1 that attach to receptors on host cells.
Blank 1: spikes, spike, or spike proteins
An enzyme that uses an RNA molecule as a template to make a complementary copy of DNA is called ______.
reverse transcriptase
Human cells are larger than viruses by which size factor?
Thousand
Why are virally encoded polymerases significant medically?
Because they are a target for antiviral drugs
Enveloped viruses have an outer layer made up of _______.
lipid
A ______ infection results from the integration of bacteriophage DNA into the chromosome of the bacterial host.
lysogenic
During viral replication, when the genome of a (+) single-stranded RNA virus is used as a template, which of the following is generated?
(-) single-stranded RNA molecules
Which of the following describes the various viral parts coming together to produce virions?
Assembly
Replication of temperate phages and lytic phages have which steps in common?
Genome entry Assembly Biosynthesis of viral components Attachment Release (Reason: Temperate phages and lytic phages do all the same sorts of things, except temperate phages can integrate their genomes into the host genome)
Why does a virus need a host cell?
It is unable to replicate on their own, and they need the intracellular environment and energy supplies to replicate. Indeed, they use the host translation machinery to synthesize their proteins, and the cell provides structures and/or host factors to achieve the synthesis of viral genomes.
What is lysogenic conversion? Give an example.
When a prophage can confer new properties on the cell because of the expression of genes on the integrated phage DNA. In all of these cases, non-lysogens cannot synthesize toxin. The genes that code for these toxins are phage genes, which are expressed only when the phage DNA is integrated into the bacterial chromosome.Ex: lysogenic strains of Streptococcus pyogenes and Clostridium botulinum manufacture toxins that are responsible for scarlet fever and botulism, respectively.
A prion is best described as ______.
a proteinaceous infectious agent
Infectious agents that have a simpler structure than viruses include ______.
both viroids and prions
The viral genome is protected from the environment by a protein shell called the ______.
capsid
A capsid is ______.
the protein coat that surrounds the viral genome
Which of the following about classifying viruses is TRUE?
- Viruses can be classified based on different viral characteristics. - An online database classifying viruses is kept by the ICTV (International Committee on Taxonomy of Viruses). - It provides a useful way to identify and study viruses.
What is reverse transcriptase? What group of viruses encode it?
Enzyme copies the single-stranded viral RNA into a complementary stand of DNA. A second strand of DNA complementary to the first strand is then synthesized. The double-stranded DNA is integrated permanently into a chromosome of the host cell as a provirus. Reverse transcriptase is usually associated with retroviruses.
Consequences of lysogeny include ______.
immunity to superinfection lysogenic conversion
What term is used to describe the transfer of genetic information from one bacterium to another bacterium by a bacteriophage?
transduction
List the steps of an animal virus infection cycle in the correct order. Start with the earliest at the top.
1. attachment 2. penetration and uncoating 3. synthesis of viral proteins and replication of the genome 4. assembly 5. release
Which of the following describes a consequence of lysogeny that could result in human disease?
Lysogenic conversion
______ is a change in the phenotype of a lysogen as a consequence of the specific prophage it carries.
Lysogenic conversion
The replication strategy of viruses can be divided into three general categories: those used by ______.
RNA viruses reverse transcribing viruses DNA viruses
Which of the following statements about virus nucleic acid is true?
Viruses contain either DNA or RNA.
A _______ is a single virus particle.
virion
How is the genome of a virus sometimes different from that of a cell?
the lack of a cellular structure. Viruses are acellular entities, meaning they don't have a cellular structure like living organisms do. This means they lack most components of cells, such as organelles, ribosomes, and the plasma membrane. Instead, a virus, or virion, is composed of a nucleic acid core, an outer protein coating or capsid, and sometimes an outer envelope made of protein and phospholipid membranes derived from the host cell. This nucleic acid core contains the genome or total genetic content of the virus.Another important distinction of viral genomes is that they can use either DNA or RNA as their genetic material, which is unlike living organisms that only use DNA.
The replication strategies of animal viruses can be divided into three general categories: those used by Blank 1 viruses, Blank 2 viruses, and reverse transcribing viruses
Blank 1: DNA Blank 2: RNA
A generalized infection cycle of an animal viruses can be divided into five steps: 1. Blank 1; 2. Blank 2 entry; 3. Blank 3; 4. assembly; and 5. Blank 4
Blank 1: attachment, attach, or adsorption Blank 2: genome Blank 3: synthesis or biosynthesis Blank 4: release or lysis
DNA viruses often encode their own Blank 1 for DNA synthesis, which allows them to replicate even if the host cell is not actively duplicating its own chromosome.
Blank 1: polymerase
RNA viruses have a higher mutation rate than DNA viruses because replicases typically lack Blank 1 ability.
Blank 1: proofreading
Reassortment of gene segments that encode viral surface proteins recognized by the immune system can result in a loss of the immune system's ability to recognize and respond to the virus. This phenomenon is called antigenic Blank 1
Blank 1: shift
Phage DNA and proteins are made during the Blank 1 step of the T4 lytic cycle.
Blank 1: synthesis or biosynthesis
Bacteriophages play a fundamental role in a type of horizontal gene transfer called Blank 1.
Blank 1: transduction
A(n) Blank 1 is an infectious agent that lacks a capsid and consists only of RNA.
Blank 1: viroid
How do viruses attach to host cells?
Protein fibers at the end of the phage tail attach to specific receptors on the bacterial cell wall and the base plate with its tail spikes settles on the surface of the bacterium.
Describe (briefly) how viruses can exit host cells.
Viruses can exit host cells because an enzyme lysozyme is t synthesized during the latter stages of the infection period.This enzyme digests the host cell wall from within, resulting in cell lysis and the release of phage. - It could also extrude from the host. After multiplying, it can leak out of the host cell without killing the host cell.
The accumulation of mutations in genes that encode viral surface proteins recognized by the immune system results in a type of antigenic variation called ______
antigenic drift
Which of the following processes are required for production of virus particles in a host cell?
Translation of viral genes Transcription of viral genes Replication of viral genome
The enzyme of RNA viruses that typically lacks proofreading ability and thus makes many mistakes compared to the polymerases of DNA viruses is _____
replicase
Attachment of animal viruses to the host cell typically occurs by means of ______.
spikes
In acute viral infections, although the infected host cells may die, the host may survive because _____
the host's immune system may gradually eliminate the virus