Chapter 19- Viruses
The nucleic acid of a virus particle is enclosed in a protein coat. What is it called?
What do we call a virus that attacks a bacterium?
phage or bacteriophage
The pointer is indicating the virus's _____.
Viral DNA makes mRNA by the process of _____.
The lytic cycle of bacteriophage infection ends with the _____.
rupture of the bacterium
The bacterium ruptures and phages are released.
The pointer is indicating the _____.
viral protein coat
the viral protein coat surrounds its genome
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.
The arrow is indicating _____.
In the lysogenic cycle _____.
viral DNA is replicated along with host DNA
Cycle A is the _____ cycle and cycle B is the _____ cycle.
lytic ... lysogenic
Sort the items according to whether they may be found only in free virus particles, only in uninfected host cells, or in both viruses and host cells.
viruses only: capsid, envelope with glycoproteins, capsomere (core protein)
host cell only: ribosome
both: DNA, RNA, Protein
The genetic material of HIV consists of _____.
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.
What is the source of a viral envelope?
host cell membrane
Which of these is reverse transcriptase?
Which of these is the viral genome?
HIV is an RNA virus.
What enzyme is responsible for the process seen here?
Reverse transcriptase catalyzes the formation of DNA from an RNA template.
Double-stranded viral DNA is incorporated into a host cell as a _____.
"Provirus" is the name given to double-stranded viral DNA that has been incorporated into a host cell's genome.
How does HIV cause disease?
HIV kills cells that defend the body against disease.
How do enveloped viruses differ from nonenveloped viruses?
They have a membrane-like outer covering.
Which replicative cycle describes a virus that can integrate its genome into the host cell's genome?
Which enzyme 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.
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.
True or false? The human immunodeficiency virus (HIV) uses reverse transcriptase to make double-stranded RNA copies of its DNA genome.
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.
Why are viruses called obligate intracellular parasites?
They must use a host cell's nucleotides for transcription and replication.
They must use a host cell's amino acids to synthesize proteins.
They must use a host cell's ribosomes to synthesize proteins.
They must use a host cell's metabolic enzymes and pathways to obtain energy.
All of the above.
Why are retroviruses considered a special class of viruses?
They transcribe RNA to DNA using reverse transcriptase.
HIV uses which of the following processes to synthesize a DNA strand using its RNA genome as a template?
What is the most effective way to stop viral infections?
Vaccines stimulate the immune system to recognize and effectively fight off invading viruses. They have proven to be the most effective weapon against viruses.
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.
The H1N1 2009 outbreak is considered to have been which of the following?
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.
Why do RNA viruses appear to have higher rates of mutation?
Replication of their genomes does not involve proofreading.
Emerging viruses arise by
the spread of existing viruses to new host species.
mutation of existing viruses.
the spread of existing viruses more widely within their host species
Which of the following characteristics, structures, or processes is common to both bacteria and viruses?
genetic material composed of nucleic acid
To cause a human pandemic, the H5N1 avian flu virus would have to
become capable of human-to-human transmission.
RNA viruses require their own supply of certain enzymes because
host cells lack enzymes that can replicate the viral genome.
How does a virus differ from a bacterium?
Viruses, unlike bacteria, lack metabolic enzymes.
Viruses lack metabolic enzymes and equipment for making proteins, such as ribosomes.
Why is it ineffective to treat viral disease with antibiotics?
Antibiotics inhibit enzymes specific to bacteria and have no effect on virally encoded enzymes.
How do prions differ from viruses?
Unlike a virus, a prion is a single molecule.
Unlike viruses, prions are infectious proteins.
Unlike viruses, prions do not include any nucleic acids.