17. Viruses

Viruses can vary with respect to all of the following characteristics except __________.

A microbiologist analyzes chemicals obtained from an enveloped RNA virus that infects monkeys. He finds that the viral envelope contains a protein characteristic of monkey cells. Which of the following is the most likely explanation?

Which of the following, if any, may be a component of a virus?

Viruses that infect bacteria are called __________.

HIV, the virus that causes AIDS, only infects certain cells within the immune system. This is because __________.

Which of the following can a virus do without a host cell?

When a virus infects an E. coli cell, what part of the virus enters the bacterial cytoplasm?

The phage reproductive cycle that kills the bacterial host cell is a __________ cycle, and a phage that always reproduces this way is a __________ phage.

In the lytic life cycle of phages, __________.

Restriction enzymes help defend bacteria against viral infections by __________.

The avian flu virus H5N1 is considered a greater long-term threat than the swine flu virus H1N1 because __________.

A new pathogenic form of influenza A can emerge when __________.

Plant viruses spread throughout the plant by way of __________.

Which of the following is an example of vertical transmission of a virus in plants?

Birds act as a natural __________ for the influenza __________ virus.

A phage that inserts itself into the host DNA is called __________.

A prophage is a(n) __________.

In the lysogenic cycle of phages, __________.

What is the origin of the phospholipid membrane that envelops many animal viruses?

What is the function of hemagglutinin in the influenza virus?

Why can flare-ups of herpesvirus infection recur throughout a person's life?

How do retroviruses, such as HIV, differ from other viruses?

Emerging viruses can originate from which of the following sources?

Reverse transcription, carried out by retroviruses, is the process by which __________.

Which statement below is a correct comparison of a "regular" RNA virus and an RNA retrovirus?

When comparing DNA and RNA viruses, which mutate more quickly, and why?

The symptoms of a viral infection in a person can be caused by __________.

Vaccines for viral diseases are __________ and help prevent infection by __________.

Prions are __________ that are thought to cause disease by __________.

What do host cells provide for viruses? a. ATP b. nucleotides and amino acids c. ribosomes d. all of the above

Which of the following characteristics, structures, or processes is common to both bacteria and viruses? a. metabolism b. ribosomes c. genetic material composed of nucleic acid d. cell division

What does reverse transcriptase do?

Emerging viruses arise by a. mutation of existing viruses. b. the spread of existing viruses to new host species. c. the spread of existing viruses more widely within their host species. d. all of the above.

In the viral replicative cycle, what reaction do viral proteases catalyze? Select True or False for each statement. T/F They catalyze polymerization of amino acids into peptides. T/F They catalyze folding of long peptide chains into functional proteins. T/F They catalyze cutting of polyprotein chains into functional proteins. T/F They catalyze breaking of peptide bonds

To cause a human pandemic, the H5N1 avian flu virus would have to a. spread to primates such as chimpanzees. b. develop into a virus with a different host range. c. become capable of human-to-human transmission. d. become much more pathogenic.

A bacterium is infected with an experimentally constructed bacteriophage composed of the T2 phage protein coat and T4 phage DNA. The new phages produced would have a. T2 protein and T4 DNA. b. T4 protein and T2 DNA. c. T2 protein and T2 DNA. d. T4 protein and T4 DNA.

What features distinguish the seven major categories of viruses?

What features distinguish the seven major categories of viruses?

The outer surface of a virion consists of either a membranous envelope or a protein capsid. How does the outer surface correlate with a virus's mode of exiting a host cell?

RNA viruses require their own supply of certain enzymes because a. host cells rapidly destroy the viruses. b. host cells lack enzymes that can replicate the viral genome. c. these enzymes translate viral mRNA into proteins. d. these enzymes penetrate host cell membranes.

Compare and contrast the bacteriophage lytic cycle and lysogeny by addressing (1) the rate of replication of the viral genome, (2) production of virions, and (3) effect on the host cell.

Compare and contrast the bacteriophage lytic cycle and lysogeny by addressing (1) the rate of replication of the viral genome, (2) production of virions, and (3) effect on the host cell.

DRAW IT Redraw Figure 19.8 to show the replicative cycle of a virus with a single-stranded genome that can function as mRNA (a class IV virus).

If you come down with the flu, should your physician prescribe an antibiotic for you? Explain why or why not.

If you come down with the flu, should your physician prescribe an antibiotic for you? Explain why or why not.

Of the viruses highlighted in Section 33.4, predict which of the following would be able to make viral proteins if nothing more than its genome were injected into a suitable host cell. a. pea mosaic ([+]ssRNA) virus b. bluetongue (dsRNA) virus c. measles ([−]ssRNA) virus d. human immunodeficiency (RNA reverse-transcribing) virus

Of the viruses highlighted in Section 33.4, predict which of the following would be able to make viral proteins if nothing more than its genome were injected into a suitable host cell. a. pea mosaic ([+]ssRNA) virus b. bluetongue (dsRNA) virus c. measles ([−]ssRNA) virus d. human immunodeficiency (RNA reverse-transcribing) virus

If you were in charge of the government's budget devoted to stemming the AIDS epidemic, would you devote most of the resources to drug development or preventive medicine? Defend your answer.

Which of the following is/are always true? a. Viruses cannot reproduce outside a host cell; b. Viruses are not surrounded by a membrane; c. Viruses are not made up of cells; d. A and C are correct; e. A, B, and C are correct

Which of the following types of viruses would you expect to require periods of latency? a. viruses that have large genomes and require a long time for replication b viruses that require a long time for transmission to new hosts c viruses that require a long time for assembly into complex structures d. viruses that infect cells of the immune system

The mosquito-borne Zika virus (ZIKV) is one of the most feared viruses for pregnant women. Recent statistics justify this fear: Infants born to mothers infected with ZIKV during pregnancy face a risk of up to 42 percent of developing birth defects, including microcephaly (an abnormally small head and decreased brain volume). What do we know about how ZIKV causes damage to the developing brain? ZIKV is a Baltimore class IV virus. Based on this classification, what do you know about the structure of its genome?

The mosquito-borne Zika virus (ZIKV) is one of the most feared viruses for pregnant women. Recent statistics justify this fear: Infants born to mothers infected with ZIKV during pregnancy face a risk of up to 42 percent of developing birth defects, including microcephaly (an abnormally small head and decreased brain volume). What do we know about how ZIKV causes damage to the developing brain? Researchers have determined that host cells possess several different surface proteins that can serve as virus receptors for ZIKV. If you were to repeat the experiment described in Figure 33.8 using ZIKV instead of HIV, how would you expect the results to be different? Explain.

The mosquito-borne Zika virus (ZIKV) is one of the most feared viruses for pregnant women. Recent statistics justify this fear: Infants born to mothers infected with ZIKV during pregnancy face a risk of up to 42 percent of developing birth defects, including microcephaly (an abnormally small head and decreased brain volume). What do we know about how ZIKV causes damage to the developing brain? Several lines of evidence suggest that after ZIKV is transmitted to a pregnant woman via the bite of an infected mosquito, the virus then directly infects cells of the placenta, gaining access to the fetal brain. Following attachment, the virion would most likely enter the placental cell by: a. insertion via the mosquito's mouthparts b. endocytosis c. degrading the cell wall with lysozyme d. injection through a hollow, needle-like protein structure

The mosquito-borne Zika virus (ZIKV) is one of the most feared viruses for pregnant women. Recent statistics justify this fear: Infants born to mothers infected with ZIKV during pregnancy face a risk of up to 42 percent of developing birth defects, including microcephaly (an abnormally small head and decreased brain volume). What do we know about how ZIKV causes damage to the developing brain? Several lines of evidence suggest that after ZIKV is transmitted to a pregnant woman via the bite of an infected mosquito, the virus then directly infects cells of the placenta, gaining access to the fetal brain. Following attachment, the virion would most likely enter the placental cell by: a. insertion via the mosquito's mouthparts b. endocytosis c. degrading the cell wall with lysozyme d. injection through a hollow, needle-like protein structure

The mosquito-borne Zika virus (ZIKV) is one of the most feared viruses for pregnant women. Recent statistics justify this fear: Infants born to mothers infected with ZIKV during pregnancy face a risk of up to 42 percent of developing birth defects, including microcephaly (an abnormally small head and decreased brain volume). What do we know about how ZIKV causes damage to the developing brain? Researchers recently developed a mouse model for fetal brain defects associated with human ZIKV infection. To determine the effect of ZIKV on the number of neurons in the brain, ZIKV was injected into the brains of developing mouse embryos. Neurons were identified by staining sections of brain tissue with antibodies against NeuN, a neuron-specific protein, and the number of NeuN-positive cells per mm2 in specific regions was quantified. The results of three independent experiments are shown in the graph below. Use the P value provided to determine if the difference is significant or not (* means P< 0.05). Based on these results, what can you conclude?

The mosquito-borne Zika virus (ZIKV) is one of the most feared viruses for pregnant women. Recent statistics justify this fear: Infants born to mothers infected with ZIKV during pregnancy face a risk of up to 42 percent of developing birth defects, including microcephaly (an abnormally small head and decreased brain volume). What do we know about how ZIKV causes damage to the developing brain? Traveling and tourism have been badly affected in ZIKV-affected countries. What advice would you give a friend planning a trip to the Caribbean?

The mosquito-borne Zika virus (ZIKV) is one of the most feared viruses for pregnant women. Recent statistics justify this fear: Infants born to mothers infected with ZIKV during pregnancy face a risk of up to 42 percent of developing birth defects, including microcephaly (an abnormally small head and decreased brain volume). What do we know about how ZIKV causes damage to the developing brain? Traveling and tourism have been badly affected in ZIKV-affected countries. What advice would you give a friend planning a trip to the Caribbean?

The mosquito-borne Zika virus (ZIKV) is one of the most feared viruses for pregnant women. Recent statistics justify this fear: Infants born to mothers infected with ZIKV during pregnancy face a risk of up to 42 percent of developing birth defects, including microcephaly (an abnormally small head and decreased brain volume). What do we know about how ZIKV causes damage to the developing brain? Draw a model to illustrate how the Zika virus genome is used to produce new virions. In your drawing, identify the steps required to replicate the genome and those used to produce mRNA. Also note where mRNAs that are used to produce capsid and envelope proteins are translated.