Viruses

Compare the structures of tobacco mosaic virus (TMV) and influenza virus (see Figure 19.3)

Bacteriophages were used to provide evidence that DNA carries genetic information (see Figure 16.4). Briefly describe the experiment carried out by Hershey and Chase, including in your description why the researchers chose to use phages.

Compare the effect on the host cell of a lytic (virulent) phage and a lysogenic (temperate) phage.

Compare the CRISPR-Cas system to the miRNA system discussed in Concept 18.3, including their mechanisms and their functions.

The RNA virus in Figure 19.8 has a viral RNA polymerase that functions in step 3 of the virus’s replicative cycle. Compare this with a cellular RNA polymerase in terms of the template and overall function. (see Figure 17.10)

Why is HIV called retrovirus?

Looking at Figure 19.9, imagine you are a researcher trying to combat HIV infection. What molecular processes could you attempt to block?

The phylogenetic tree shows the hypothesized evolutionary relationship between the variant strains of the H1N1 virus. The more closely connected the two variants are, the more alike they are in terms of HA gene sequence. Each fork in a branch, called a node, shows where two lineages separate due to different accumulated mutations. The length of the branches is a measure of how many sequence differences there are between the variants, indicating how distantly related they are. Referring to the phylogenetic tree, which variants are more closely related to each other: A/Taiwan/1018/2011 and A/Taiwan/552/2011 or A/Taiwan/1018/2011 and A/Taiwan/8542/2009? Explain your answer.

The scientists arranged the branches into groups made up of one ancestral variant and all of its descendants, mutated variants. They are color-coded in the figure. Using group 11 as an example, trace the lineage of its variants. (a) Do all of the nodes have the same number of branches or branch tips? (b) Are all of the branches in the group the same length? (c) What do these results indicate?

The graph at the lower left shows the number of isolates collected (each from an ill patient) on the y-axis and the month and year that the isolates were collected on the x-axis. Each group of variants is plotted separately with a line color that matches the tree diagram. (a) Which group of variants was the earliest to cause the first wave of H1N1 flu in over 100 patients in Taiwan? (b) After a group of variants had a peak number of infections, did members of that same group cause another (later) wave of infection? (c) One variant in group 1 (green, upper-most branch) was used to make a vaccine that was distributed very early in the pandemic. Based on the graphed data, does it look like the vaccine was effective?

Groups 9, 10, and 11 all had H1N1 variants that caused a large number of infections at the same time in Taiwan. Does this mean that the scientists’ hypothesis that new variants cause new waves of infection was correct? Explain your answer.

Describe two ways in which a pre-existing virus can become an emerging virus.

Contrast horizontal and vertical transmission of viruses in plants.

TMV has been isolated from virtually all commercial tobacco products. Why, then, is TMV infection not an additional hazard for smokers?

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

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.

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.

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.

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).

The success of some viruses lies in their ability to evolve rapidly within the host. Such viruses evade the host's defences by mutating and producing many altered progeny viruses before the body can mount an attack. Thus, the viruses present late in infection differ from those that initially infected the body. Discuss this as an example of evolution in a microcosm. Which viral lineages tend to predominate?

When bacteria infect an animal, the number of bacteria in the body increases in an exponential fashion (graph A). After infection by a virulent animal virus with a lytic replicative cycle, there is no evidence of infection for a while. Then the number of viruses rises suddenly and subsequently increases in a series of steps (graph B). Explain the difference in the curves.

While viruses are considered by most scientists to be nonliving, they do show some characteristics of life, including the correlation of structure and function. In a short essay (100–150 words), discuss how the structure of a virus correlates with its function.

Oseltamivir (Tamiflu), an antiviral drug prescribed for influenza, inhibits the enzyme neuraminidase. Explain how this drug could prevent infection in someone exposed to the flu or could shorten the course of flu in an infected patient (the reasons for which it is prescribed).