Chapter 19 Quiz

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.

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.

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

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.

replicate only by a lytic cycle.

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.

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.

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

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

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

The viral envelope is derived from host cell membrane.

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.

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.

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

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

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

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.

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.

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

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

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

a plant inherits a viral infection from a parent

The viral infection was acquired by vertical transmission.

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

are infections proteins that spread disease

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.

Linear DNA circularizes.

rupture of the bacterium

viral protein coat (head)

The host cell's DNA is destroyed.

-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."

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

vaccines