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