Genetics Ch18
Prophage DNA in a lysogenic bacterium is replicated ________
when the bacterial cell prepares to divide
Which of the following are examples of emerging viruses? -H1N1 (swine flu) -Zika virus -Epstein-Barr virus (which causes mononucleosis) -Tobacco mosaic virus (which infects many types of plants) -Varicella zoster (which causes chickenpox) -HIV (which causes AIDS)
-H1N1 (swine flu) -Zika virus -HIV (which causes AIDS)
T/F: In order for new HIV particles to be assembled, the viral DNA must be excised from the host cell's chromosome.
False -- The HIV DNA incorporated into a chromosome can be transcribed within the host cell's nucleus so that viral RNA and protein molecules can be produced. The viral DNA is not excised from the host cell chromosome.
T/F: The genome of a virus is always a circular molecule of either DNA or RNA.
False -- can be DNA or RNA and circular or linear
A new strain of influenza virus that infects humans but carries two genes normally found in flu viruses that infect pigs, is identified as ________
H1N1
During lysogeny, how is prophage DNA replicated?
It is copied when the host cell's DNA is replicated.
What does it mean to say that a virus is latent?
Its genome is integrated into a host cell chromosome, and the virus is inactive.
What is the result of the lytic cycle of bacteriophage λ?
Lysis of the host cell and release of new bacteriophages
In a cell infected with HIV, how are new viruses produced?
Viral DNA in the host cell chromosome is transcribed into RNA.
During the assembly of HIV, capsid proteins assemble around reverse transcriptase, integrase, and viral RNA. The virus acquires an outer envelope in a process called ______________
budding
Arrange the steps that occur during synthesis of new bacteriophage λ viruses in the correct order
1. Prophage DNA is excised from the bacterial chromosome 2. Host cell enzymes copy phage DNA and transcribe the viral genes into mRNA 3. Host cell ribosomes translate viral mRNA into proteins
A prophage or provirus can remain inactive, or _____________, for long periods of time.
latent
Which of the following describe possible structures of the genome of a virus? -Multiple select question. -Linear -Circular -Spiky -Polyhedral
linear circular
A viral envelope is made of a ______ embedded with virally encoded spike glycoproteins.
lipid bilayer
The viral reproductive cycle in which bacteriophage DNA is incorporated into the host cell's DNA but new phages are not made immediately is called the _______________cycle.
lysogenic
In bacteriophages, another term for latency is _____________
lysogeny
In order for bacteriophage λ to be released from a bacterial cell, a phage enzyme called _________________ digests the bacterial cell wall, which causes the bacterial cell to burst
lysozyme
The reproductive cycle of phage λ that results in the release of new phage particles is called the ____________ cycle
lytic
Attachment of a virus to a host cell is specific because the virus must bind to specific ______________ on the surface of the host cell.
molecules/proteins/receptors
Because reverse transcriptase is unable to proofread, HIV has a very high _______________ rate
mutation
The term "host range" describes the ______________ by a virus.
number/type of species that can be infected
Viral DNA that is integrated into a chromosome in a eukaryotic cell is called a(n) _________
provirus
In order for new bacteriophage λ components to be produced and assembled, the prophage must be _________________ from the bacterial chromosome.
removed
The series of steps that occurs involving infection of a host cell, expression of viral genes, and production of new viruses is called the viral _____________ ____________.
reproductive cycle
In order for double-stranded HIV DNA to be incorporated into a host cell chromosome, DNA must be synthesized from an RNA template by the enzyme ____________ _______________.
reverse transcriptase
The viral enzyme that uses a viral RNA strand as a template for the synthesis of a complementary copy of DNA is called _____________ _____________
reverse transcriptase
After a viral genome enters a host cell, viral genes may be expressed immediately due to the activity of host cell enzymes and _______________, which can begin synthesizing viral proteins.
ribosomes
When phage λ infects a bacterial cell, it attaches to the surface of the host cell. Next, the phage coat proteins undergo a conformational change in which the ____________ of the phage contracts, allowing the phage to inject its _______________ into the bacterial cytoplasm.
shaft; DNA/genome
The genome of human immunodeficiency virus consists of ____________. It is an ______________ virus.
single stranded RNA; enveloped
In terms of size, a virus is _________
smaller than all cells
Place the steps that occur during the reproductive cycle of phage λ in the correct order
1. Phage binds to proteins in the bacterial cell membrane 2. Phage DNA is injected into the cytoplasm 3. Viral DNA and proteins are synthesized, and the host chromosomal DNA is digested 4. Phage components are assembled into new phages
What happens during the lysogenic cycle? -The bacteriophage DNA remains in the cytoplasm, separate from the bacterial chromosome. -New phages are not made. -Viral DNA is used to synthesize viral RNA and protein molecules. -Viral DNA is incorporated into the host cell's chromosome. -The host cell is killed. -New phages are assembled and released.
-New phages are not made. -Viral DNA is incorporated into the host cell's chromosome.
What components of tobacco mosaic virus can be mixed together to reconstitute an intact virus? -Glycoproteins -RNA -Phospholipids -DNA -Capsid proteins
-RNA -capsid proteins
Which of the following are reasons that viruses are considered nonliving? -They cannot maintain homeostasis. -They cannot reproduce by themselves. -They are not made of cells. -They cannot carry out metabolic reactions by themselves. -They do not contain DNA or RNA.
-They cannot maintain homeostasis. -They cannot reproduce by themselves. -They are not made of cells. -They cannot carry out metabolic reactions by themselves.
When HIV is assembled at the plasma membrane, what viral components become enclosed by capsid proteins and an outer envelope? -Viral RNA -Reverse transcriptase -Fragments of the host cell's chromosomes -Integrase -RNA polymerase
-Viral RNA -Reverse transcriptase -Integrase
Phage λ cannot self-assemble because assembly of new viral particles requires the function of ______. -enzymes that modify capsid proteins -proteins that serve as scaffolding for capsid assembly -nucleases encoded by the host cell genome -reverse transcriptase
-enzymes that modify capsid proteins -proteins that serve as scaffolding for capsid assembly
Arrange the steps that occur when HIV infects an animal cell in the correct order
1. Spike glycoproteins bind to receptors on the plasma membrane of the host cell 2. The viral envelope fuses with the host cell's membrane 3. The viral capsid, containing RNA and viral proteins, is released into the cytosol. 4. Cellular enzymes remove capsid proteins 5. Two copies of viral RNA and enzymes (reverse transcriptase, and integrase) are released into the cytosol
The diameter of a virus is usually around ______ nm.
20-400
What type of cell can be infected by a bacteriophage?
A bacterial cell
How are new bacteriophage λ particles released from a host cell?
A phage enzyme breaks down the bacterial cell wall, causing the cell to burst.
What is the difference between a temperate phage and a virulent phage?
A virulent phage has only a lytic cycle, while a temperate phage has both a lytic and a lysogenic cycle.
What is an emerging virus?
A virus that has arisen recently and is likely to cause infection
What is a retrovirus?
A virus with a genome made of RNA that copies its genome by reverse transcription
Which of the following molecules can serve as the genetic material of a virus? -DNA -Glycoprotein -Phospholipid -RNA -Protein
DNA RNA
After a virus attaches to a host cell, its _________ enters the host cell.
DNA/genome/RNA
The genome of a virus can be made of either _______________ or __________.
DNA; RNA
What is a prophage?
Phage DNA integrated into a bacterial chromosome
Which of the following events occurs only during the lysogenic cycle and not during the lytic cycle? -Phage DNA integrates into the host chromosome. -Phage DNA is injected into the cytoplasm of a bacterial cell. -DNA of the host cell is digested into fragments. -New phages are released.
Phage DNA integrates into the host chromosome.
In order for the tobacco mosaic virus to self-assemble in vitro, what two viral components need to be mixed together? DNA Glycoproteins Phospholipids RNA Capsid proteins
RNA capsid proteins
When a cell becomes infected by a virus, when and how are the viral genes expressed in the cell?
They can be expressed immediately by host cell enzymes and ribosomes.
When phage λ attaches to a host cell, what occurs that allows the phage DNA to be injected into the bacterial cytoplasm?
The phage coat proteins change their conformation.
What is a capsid?
The protein coat of a virus
When a cell becomes infected with a virus, what happens after the virus attaches to the host cell?
The viral DNA or RNA enters the host cell.
Which emerging virus can cause severe fetal brain defects, including microencephaly?
Zika
Which emerging virus is spread by mosquitoes of the genus Aedes?
Zika
What is a host cell?
a cell infected by a virus
Many animal viruses have a viral envelope that encloses the capsid. This envelope contains spike glycoproteins that are embedded in _________
a lipid bilayer derived from the plasma membrane of the host cell
Adenovirus, which is shown here, is an example of __________
a nonenveloped virus with a polyhedral capsid and protein fibers with knobs
During assembly of HIV, reverse transcriptase, integrase, and viral RNA become enclosed in capsid proteins. Where does the assembly process occur?
at the plasma membrane
A virus that infects bacteria is called a(n) _____________
bacteriophage
Viruses can only infect certain types of cells because proteins in the virus must __________
bind to specific molecules on the surface of the host cell
Evidence suggests that HIV is related to simian immunodificiency virus (SIV) that infects chimpanzees. Humans in West Africa hunt chimpanzees for meat and likely acquired the virus through contact with the ____________ of SIV-infected chimpanzees.
blood
Picture: Illustration shows an enveloped virus releasing from an animal cell. The mechanism used by virus is budding. In this process, the virus is enfolded in the plasma membrane of animal cell and buds out of the cell syrface. They don't lyse the cell. As shown in the image, the process in which new HIV particles are released from an infected cell is called ______.
budding
Capsomers are proteins that make up the viral _________
capsid
Reconstituted tobacco mosaic viruses can be made by the self-assembly of purified _____________ and ________________ molecules from different viruses. The RNA composes the genome
capsid proteins; RNA
Phage λ, a virus that infects bacterial cells, has a genome made of _________
double-stranded DNA
HIV, H1N1, and Zika virus all infect humans. Because these viruses have all arisen relatively recently, they are all considered to be ______________ viruses.
emerging
During the assembly of phage λ, capsid proteins are modified by ________________ produced by the host cell.
enzymes
When a human virus is latent its genetic material is either integrated into the host ____________ or maintained as an independently replicating genetic element called a(n) _____________
genome; episome
This diagram shows the structure of the tobacco mosaic virus. The capsid of this virus is best described as _________
helical
HIV severely compromises the immune system because it infects ___________T cells that interact with other immune cells.
helper
When a bacterial cell is infected with phage λ, the phage DNA may integrate into the bacterial chromosome with the aid of an enzyme called ____________
integrase
Researchers reconstituted TMV virus by mixing RNA and proteins from the wild-type virus and the HR strain, which has capsid protein containing the amino acids methionine and histidine (two amino acids not found in the wild-type capsid proteins). The reconstituted viruses were allowed to infect tobacco leaves. Based on the data in the table, the scientists could conclude that _______________
the genetic material of the virus was made of RNA
A nonliving infectious particle with a genome composed of nucleic acid is called a(n) _____________
virus
