Chapter 19 Viruses

Why is combination drug therapy for HIV/AIDS less likely to lead to resistance than single drug therapy?

The likelihood of one virus spontaneously mutating to be resistant to several different drugs at the same time is extremely small.

Homeostasis is a living organism's

ability to maintain constant internal conditions even when environmental conditions change.

What is the most effective way to stop viral infections?

vaccines

In the lysogenic cycle _____.

viral DNA is replicated along with host DNA

The pointer is indicating the _____. The figure shows a particle, which consists of a hexagonal head, pointed by the arrow, a collar, a tail, and several tail fibres at the end.

viral protein coat the viral protein coat surrounds its genome

The genetic material of HIV consists of _____.

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

How does a virus differ from a bacterium? Select all that apply.

- Viruses, unlike bacteria, lack metabolic enzymes Viruses lack metabolioc enzymes and equipment from making proteins, such as ribosomes

Approximately how many people worldwide are infected with AIDS?

60 million

Which of these binds to receptor molecules on the host cell membrane? The figure shows the structure of the retrovirus, HIV. Letters from A to E mark definite structures. Letter A marks the fungiform structures on the viral envelope. Letter B marks the envelope of the HIV. Letter C marks small spherical structure near viral genome. Letter D marks the envelope that surrounds the viral genome. Letter E marks spirally curved filamentous structures inside the viral particle.

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

How long must AIDS patients take their medication?

For the rest of their life.

All of the statements below are true. Select the statement that best supports the view of most biologists that viruses are nonliving. An isolated virus is unable to replicate its genes or regenerate ATP. The viral genome may be single-stranded or double-stranded RNA or DNA. Viruses are obligate intracellular parasites.

An isolated virus is unable to replicate its genes or regenerate ATP. Viruses are unable to replicate their genes or carry out any metabolic activities outside of a host cell, and this is why most biologists do not consider viruses to be alive. *Read about biologists' view of viruses in the chapter introduction*

Why is it ineffective to treat viral disease with antibiotics?

Antibiotics inhibit enzymes specific to bacteria and have no effect on virally encoded enzymes.

Which of the following is true? Kaposi's sarcoma causes AIDS. Kaposi's sarcoma is a drug to treat AIDS. Kaposi's sarcoma is only seen in AIDS patients. Kaposi's sarcoma is a symptom of AIDS.

Kaposi's sarcoma is a symptom of AIDS.

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

Linear DNA circularizes.

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.

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.

Why are viruses called obligate intracellular parasites?

They must use a host cell's amino acids to synthesize proteins. They must use a host cell's metabolic enzymes and pathways to obtain energy. They must use a host cell's ribosomes to synthesize proteins. They must use a host cell's nucleotides for transcription and replication. All of the above.

Why are retroviruses considered a special class of viruses?

They transcribe RNA to DNA using reverse transcriptase.

How do prions differ from viruses? Select all that apply.

Unlike viruses, prions are infectious proteins. Unlike viruses, prions do not include any nucleic acids. Unlike a virus, a prion is a single molecule.

Identify all correct statements about how viroids differ from viruses. Select all that apply.

Unlike viruses, viroids cause plant disease

Which of the following statements about viruses is FALSE? If a virus mutates, the immune system may not recognize the virus. People can get colds and flus again because the viruses are constantly mutating. The widespread use of antibiotics has led to resistant strains of viruses. Vaccines are available to prevent several diseases caused by viruses.

Vaccines are available to prevent several diseases caused by viruses.

Which of the following can be found in bacteria, but not viruses?

a cell membrane

The H1N1 2009 outbreak is considered to have been which of the following?

a pandemic

You are an epidemiologist studying a new disease very similar to AIDS. Most likely, this new disease is caused by what?

a retrovirus

Suppose you were in charge of sending an unmanned space probe to a new planet in search of life. The probe would be able to collect and test samples and make observations, but the planet is too far away for the probe to be able to bring samples back to Earth. The probe is small and would only be able to run a few tests, so you want to pick a test for evidence of life that is broad enough to incorporate all forms of life as we know it. Which one of the following tests would be the best to use in this situation?

a test for the presence of cells that contain DNA

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

become capable of human-to-human transmission.

AIDS can be contracted by contact with which of the following? blood or semen saliva or blood tears or vaginal secretions semen or tears

blood or semen

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

capsid

Which of the following is NOT a characteristic of living things? exhibiting complex organization creating energy having DNA as a genetic code being capable of reproduction responding to stimuli

exhibiting complex organization

Which of the following characteristics, structures, or processes is common to both bacteria and viruses?

genetic material composed of nucleic acid

The pointer is indicating the virus's _____. The figure shows a particle, which consists of two wavy strands, pointed by the arrow and with an envelope around it.

genome

RNA viruses require their own supply of certain enzymes because

host cells lack enzymes that can replicate the viral genome.

Cycle A is the _____ cycle and cycle B is the _____ cycle. The figure shows two viral cycles A and B. During cycle A, virus enters the cell and replicates using the resources of the cell. Then numerous viral particles are released from the cell by lysis. During cycle B after the entrance and uncoating, viral genome integrates into the DNA of the cell and replicates with it.

lytic ... lysogenic

Viruses are

not alive because they are not made of cells and require a host cell for reproduction.

What do we call a virus that attacks a bacterium?

phage or bacteriophage

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

reverse transcription

The lytic cycle of bacteriophage infection ends with the _____.

rupture of the bacterium The bacterium ruptures and phages are released.

As a result of the lytic cycle, _____.

the host cell's DNA is destroyed The host cell's DNA is destroyed, and ultimately, the host cell itself is destroyed in the lytic cycle.

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. all of the above

Viral DNA makes mRNA by the process of _____.

transcription