Chapter 19 Quiz

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To cause a human pandemic, the H5N1 avian flu virus would have to

become capable of human-to-human transmission.


the entirety of an organism’s heredity informatioin. It is encoded either in DNA or, for many type of viruses, in RNA.


a small infectious agent that replicates only inside the living cells of other organisms. Virus can infect all types of life forms, from animals and plants to bacteria and archaea.

Bacteriophage (phage)

is a virus that infects and replicates within bacteria. Bacteriophanges are composed of proteins that encapslate a DNA or RNA genome, and may have relatively simple or elaborate structures. Their genomes may encode as few as four genes and as many as hundreds of gene. Phage replicate witin bacteria following the injection of their genome into cytoplasm. Bacteriaphage are among the most common and diverse entities in the biosphere.


refers to the breaking down of a cell, often by viral, ezymic, or osmotic mechanisms that compromise its integrity.

Lytic cycle

The lytic cycle result in the destruction of the infected cell and its membrane.

Lysogenic cycle

is characterized by integration of the bacteriophage nucleic acid into the host bacterium’s genome or formation of a circular replicon in the bacterium’s cytoplames.The key difference between the lytic cycle and the lysogenic cycle is that the lysogenic cycle does not lyse the host cell.

Virulent phages

replicate only by a lytic cycle.

Temperate phages

use both lytic and lysogenic cycles.


Bacteriophages, which contain double-stranded DNA, can reproduce by two alternative mechanisms: the lytic cycle and the lysogenic cycle. •In the lytic cycle, virus parts are made, new viruses are assembled, and the cell is lysed, releasing the newly assembled viruses. •In the lysogenic cycle, the viral DNA incorporates into the bacterial DNA and is passed on to daughter bacterial cells when the infected bacteria reproduce normally. Occasionally, an infected bacterium in the lysogenic cycle can enter the lytic cycle, in which viral particles are produced and the cell is eventually ruptured.

Non enveloped and enveloped virus

Viruses are classified into two major groups: nonenveloped and enveloped. •Nonenveloped viruses (a) typically exit the host cell by bursting through the plasma membrane. •Enveloped viruses (b) generally escape from the host cell by budding. Because of this, the viral envelope is often derived from the host cell’s plasma membrane.


is a single stranded RNA virus that stores its nucleic acid in the form of an mRNA genome and targets a host cell as an obligate parasite.


is a genome that is integrated into the DNA of host cell.

The genetic material of HIV consists of _____.

single-stranded RNA -The genetic material of HIV consists of two molecules of single-stranded RNA.

Which of these binds to receptor molecules on the host cell membrane?

Glycoproteins on the viral envelope recognize and bind to receptors on the host cell.

What is the function of reverse transcriptase?

It catalyzes the formation of DNA from an RNA template. -This is the function of reverse transcriptase.

What is the source of a viral envelope?

The viral envelope is derived from host cell membrane.

HIV uses which of the following processes to synthesize a DNA strand using its RNA genome as a template?

reverse transcription -Retroviruses are equipped with an enzyme called reverse transcriptase, which makes a DNA copy of an RNA template, providing information flow from RNA to DNA.


The human immunodeficiency virus infects cells of the human immune system. Its primary targe is a subset of lymphocytes called helper T cells, or CD4* T cells, so named because of the CD4 proteins that stud their surface.


is an enzyme produced by a retrovirus that enables its genetic material to be integrated into the DNA of the infected cell. (transport the transcribed DNA to the cell’s DNA and integrates it) It typically lay dormant. However, if the T cells is activated by growth faters, cytokines, or antigens, the cell’s transcriptional machinery increases the rate of transcription of viral DNA into messenger RNA.

How does HIV cause disease?

HIV kills cells that defend the body against disease. -HIV affects the immune system and kills cells that protect the body from foreign bacteria and viruses.

How do enveloped viruses differ from nonenveloped viruses?

They have a membrane-like outer covering. -Enveloped viruses have a membrane-like outer covering (an envelope) surrounding their capsid.

Which replicative cycle describes a virus that can integrate its genome into the host cell’s genome?

Lysogenic -A lysogenic virus can integrate its genome into the host cell’s genome and be duplicated by the host cell’s replication machinery.

Which enzyme inserts viral DNA into the host’s chromosomal DNA?

Integrase inserts viral DNA into the host’s chromosomal DNA.

How does HIV bind to a host cell?

The viral envelope proteins interact with CD4 and a co-receptor on the cell membrane. -The viral envelope proteins gp120 and gp41 interact with CD4 and a co-receptor on the host-cell membrane.

Which of the following events stimulates the production of viral particles in a host cell?

Activation of the host cell by cytokines, growth factors, or antigens. -Activation of the host immune cell by cytokines, growth factors, or antigens causes viral DNA to be transcribed at high rates in preparation for viral production.

True or false? The human immunodeficiency virus (HIV) uses reverse transcriptase to make double-stranded RNA copies of its DNA genome.

False -A retrovirus such as HIV has an RNA genome and uses reverse transcriptase to make double-stranded DNA copies of the genome, which can then be integrated into the host cell’s genome.


occurs when new cases of a certain disease, in a given human population, and given a given period, substantially exceed what is expected based on recent experience.


is a epidemic of infectious disease that has spread through human populations across a large region; up to worldwide

The nucleic acid of a virus particle is enclosed in a protein coat. What is it called?

capsid -The protein shell that encloses a viral genome is a capsid.

horizontal transmission

A plant is infected with a virus by an external source.

Vertical transmission

a plant inherits a viral infection from a parent

A plant that has been raised in a sterile environment shows symptoms of a viral infection. How would you explain this?

The viral infection was acquired by vertical transmission.

Viral DNA makes mRNA by the process of _____.

transcription -Viral DNA co-opts the cell’s reproductive machinery.


are infections proteins that spread disease

How do prions, which are misfolded proteins, infect organisms?

Prions enter brain cells and cause normal forms of the protein to refold into the prion form. -Prions are a misfolded version of a protein normally found in the brain. When prions come into close proximity with the normal proteins, they cause them to refold into the prion form.

What happens first when a phage infects a bacterial cell and is going to enter a lysogenic cycle?

Linear DNA circularizes.

The lytic cycle of bacteriophage infection ends with the _____.

rupture of the bacterium

The pointer is indicating the _____.

viral protein coat (head)

As a result of the lytic cycle, _____.

The host cell’s DNA is destroyed.

Emerging viruses arise by

-the spread of existing viruses more widely within their host species. -the spread of existing viruses to new host species. -mutation of existing viruses.


Viral DNA incorporated into host DNA is referred to as a "prophage."

In the lysogenic cycle _____.

viral DNA is replicated along with host DNA -Viral DNA, incorporated into host DNA as a prophage, is replicated along with host DNA.

What is the most effective way to stop viral infections?


Why doesn’t a clone in nuclear transplantation resemble the surrogate mother?

The nucleus is the package of DNA and the surrogate mother only houses the zygote’s development she doesn’t contribute to the cell’s characteristics that has to do with the nucleus. The unfertilized egg has no nucleus therefore it’s only being manipulated thus, there’s no DNA. Therefore, the clone would exhibit characteristics of the genetic donor, not the surrogate.

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