1. Viruses

2. Which of the following is a property of life shared by prokaryotic cells and eukaryotic cells, but not viruses?
nucleic acids used to store hereditary information
order and complexity in arrangement of biological molecules
the ability to process energy through metabolic reactions
the capacity to evolve
Answer: C

3. Which of the following is a property of life shared by prokaryotic cells and eukaryotic cells, but not viruses?
nucleic acids used to store hereditary information
order and complexity in arrangement of biological molecules
the ability to process energy through metabolic reactions
the capacity to evolve 3

4. Which of the following is characteristic of the lytic cycle?
Viral DNA is incorporated into the host genome.
The virus-host relationship usually lasts for generations.
A large number of phages are released at a time.
Many bacterial cells containing viral DNA are produced.
The viral genome replicates without destroying the host.
Answer: C
Concept 19.2 4

5. Which of the following is characteristic of the lytic cycle?
Viral DNA is incorporated into the host genome.
The virus-host relationship usually lasts for generations.
A large number of phages are released at a time.
Many bacterial cells containing viral DNA are produced.
The viral genome replicates without destroying the host. 5

6. What is the function of reverse transcriptase in retroviruses?
It converts host cell RNA into viral DNA.
It hydrolyzes the host cell's DNA.
It uses viral RNA as a template for making complementary RNA strands.
It translates viral RNA into proteins.
It uses viral RNA as a template for DNA synthesis.
Answer: E
Concept 19.2 6

7. What is the function of reverse transcriptase in retroviruses?
It converts host cell RNA into viral DNA.
It hydrolyzes the host cell's DNA.
It uses viral RNA as a template for making complementary RNA strands.
It translates viral RNA into proteins.
It uses viral RNA as a template for DNA synthesis. 7

8. Why are viruses referred to as obligate parasites?
They use the host cell to reproduce.
Viral DNA always inserts itself into host DNA.
They invariably kill any cell they infect.
They can incorporate nucleic acids from other viruses.
They must use enzymes encoded by the virus itself.
Answer: A 8

9. Why are viruses referred to as obligate parasites?
They use the host cell to reproduce.
Viral DNA always inserts itself into host DNA.
They invariably kill any cell they infect.
They can incorporate nucleic acids from other viruses.
They must use enzymes encoded by the virus itself. 9

10. Which of the following molecules make up the viral envelope?
viral glycoproteins
capsid
phospholipids from human host cell membrane
membrane proteins from human host cell
viral DNA
Answer: A, C, D 10

11. Which of the following molecules make up the viral envelope?
viral glycoproteins
capsid
phospholipids from human host cell membrane
membrane proteins from human host cell
viral DNA 11

12. You have isolated viral particles from a patient, but you are not sure whether they are adenoviruses or influenza viruses. The presence of which class of biological molecules would allow you to distinguish between the two types of virus?
RNA
phospholipids
proteins
glycoproteins
DNA
Answer: B
Students will need to recognize that influenza viruses have an envelope, but adenoviruses do not. 12

13. You have isolated viral particles from a patient, but you are not sure whether they are adenoviruses or influenza viruses. The presence of which class of biological molecules would allow you to distinguish between the two types of virus?
RNA
phospholipids
proteins
glycoproteins
DNA 13

14. The HIV virus attacks only a certain type of white blood cells, and not other cell types. Why?
HIV receptors are not found on the other cell types.
Reverse transcriptase cannot transcribe RNA to DNA.
Viral mRNA cannot be transcribed from the integrated provirus.
Viruses cannot bud from the host cell.
Answer: A
Concept This question examines the concept that viruses are able to recognize and attach to host cells via receptor proteins and recognition molecules on the plasma membrane. 14

15. The HIV virus attacks only a certain type of white blood cells, and not other cell types. Why?
HIV receptors are not found on the other cell types.
Reverse transcriptase cannot transcribe RNA to DNA.
Viral mRNA cannot be transcribed from the integrated provirus.
Viruses cannot bud from the host cell. 15

16. Which is not an accepted theory about the evolution of viruses:
Viruses originated from naked bits of cellular nucleic acids.
Genes coding for capsid proteins allowed viruses to bind cell membranes.
Plasmids and transposons may have been the original sources of viral genomes.
Viruses are the descendents of precellular life forms.
Answer: D

17. Which is not an accepted theory about the evolution of viruses:
Viruses originated from naked bits of cellular nucleic acids.
Genes coding for capsid proteins allowed viruses to bind cell membranes.
Plasmids and transposons may have been the original sources of viral genomes.
Viruses are the descendents of precellular life forms.

18. AZT is a nucleoside analog used to treat HIV infections
AZT is a nucleoside analog used to treat HIV infections. It is a modified nucleoside. Which step does AZT hamper in the reproductive cycle of the HIV virus?
entry into the cell
synthesis of DNA from RNA catalyzed by reverse transcription
transcription of RNA from proviral DNA
viral assembly within the cell
Answer: B
Concept Because AZT is a thymine nucleoside, it will specifically block reverse transcription from RNA to DNA. 18

19. AZT is a nucleoside analog used to treat HIV infections
AZT is a nucleoside analog used to treat HIV infections. It is a modified nucleoside. Which step does AZT hamper in the reproductive cycle of the HIV virus?
entry into the cell
synthesis of DNA from RNA catalyzed by reverse transcription
transcription of RNA from proviral DNA
viral assembly within the cell 19

20. Which of the following most likely describes the vertical transmission of a plant virus?
The plant shows symptoms of disease after being grazed on by herbivores.
Sap from one plant is rubbed on the leaves of a second plant; both plants eventually show disease symptoms.
Seeds are planted and reared under protected conditions, but mature plants show disease symptoms.
After a gardener prunes several plants with the same shears, they all show disease symptoms.
Answer: C
Concept Students will need to distinguish between horizontal transmission of disease and vertical transmission. 20

21. Which of the following most likely describes the vertical transmission of a plant virus?
The plant shows symptoms of disease after being grazed on by herbivores.
Sap from one plant is rubbed on the leaves of a second plant; both plants eventually show disease symptoms.
Seeds are planted and reared under protected conditions, but mature plants show disease symptoms.
After a gardener prunes several plants with the same shears, they all show disease symptoms. 21

22. Scientific Skills Exercises
The phylogenetic tree shows the hypothesized evolutionary relationship between the variant strains of H1N1 virus. Each branch tip is one variant of the H1N1 virus with a unique HA gene sequence. The more closely connected 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 number of nodes separating two variants is an indication of how many DNA sequence differences there are between the variants, thus how distantly related they are.

23. Referring to the phylogenetic tree on the previous slide, which variant is more closely related to A/Taiwan1018/2011 in group 9 (brown): A/Taiwan/552/2011 or A/Taiwan/8542/2009?
A/Taiwan/8542/2009; variants 1018/2011 and 8542/2009 share a more recent common ancestor than is shared with variant 552/2011.
A/Taiwan/8542/2009; the node connecting variants 1018/2011 and /2009 is closer to the root of the tree.
A/Taiwan/552/2011; variant 552/2011 was collected the same year as variant 1018/2011 (in 2011), but variant 8542/2009 was collected in
A/Taiwan/552/2011; variants 1018/2011
and 552/2011 share a more recent
common ancestor than is shared with
variant 8542/2009.
Answer: D

24. Referring to the phylogenetic tree on the previous slide, which variant is more closely related to A/Taiwan1018/2011 in group 9 (brown): A/Taiwan/552/2011 or A/Taiwan/8542/2009?
A/Taiwan/8542/2009; variants 1018/2011 and 8542/2009 share a more recent common ancestor than is shared with variant 552/2011.
A/Taiwan/8542/2009; the node connecting variants 1018/2011 and /2009 is closer to the root of the tree.
A/Taiwan/552/2011; variant 552/2011 was collected the same year as variant 1018/2011 (in 2011), but variant 8542/2009 was collected in
A/Taiwan/552/2011; variants 1018/2011
and 552/2011 share a more recent
common ancestor than is shared with
variant 8542/2009.

25. The scientists arranged the branches into groups made up of one ancestral variant and all of its descendant, mutated variants. They are color-coded in the tree. Do all of the groups have the same number of branches or branch tips? What does this result indicate?
No; some of the groups died off before the others, so they could not undergo any further mutations.
Yes; all of the groups arose at about the same time.
Yes; all of the groups experienced the same mutation rate.
No; some groups experienced a higher mutation rate than others.

26. The scientists arranged the branches into groups made up of one ancestral variant and all of its descendant, mutated variants. They are color-coded in the tree. Do all of the groups have the same number of branches or branch tips? What does this result indicate?
No; some of the groups died off before the others, so they could not undergo any further mutations.
Yes; all of the groups arose at about the same time.
Yes; all of the groups experienced the same mutation rate.
No; some groups experienced a higher mutation rate than others.

27. The scientists also graphed the H1N1 isolates by the month and year of isolate collection, which reflects the time period in which each viral variant was actively causing illness in people. The graph shows the number of isolates collected from ill patients (one isolate per 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 phylogenetic tree diagram.

28. Which group of variants was the earliest to cause H1N1 flu in over 100 patients in Taiwan?
Groups 1, 3, and 6 (green line)
Group 7 (black line)
Group 8 (dark blue line)
Group 11 (red line)
Answer: B

29. Which group of variants was the earliest to cause H1N1 flu in over 100 patients in Taiwan?
Groups 1, 3, and 6 (green line)
Group 7 (black line)
Group 8 (dark blue line)
Group 11 (red line)
Answer: B

30. Once a group of variants had a peak number of infections, did members of that same group cause another wave of infection?
No, each group of variants caused only one wave of infection.
Yes, one group of variants caused multiple waves of infection.
This is not discernable from the graph.
Answer: A

31. Once a group of variants had a peak number of infections, did members of that same group cause another wave of infection?
No, each group of variants caused only one wave of infection.
Yes, one group of variants caused multiple waves of infection.
This is not discernable from the graph.

32. Consider the data from both the phylogenetic tree and the graph
Consider the data from both the phylogenetic tree and the graph. 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 incorrect?
Their hypothesis was incorrect; the graph clearly shows three distinct peaks occurring in the same wave.
Their hypothesis was still supported; each of these three groups has a different height peak.
Their hypothesis was incorrect; all three groups are rooted in the same phylogenetic tree but caused three distinct peaks in the same wave.
Their hypothesis was still supported; these three groups arose along different lineages but emerged to cause illness during the same wave.
Answer: D

33. Consider the data from both the phylogenetic tree and the graph
Consider the data from both the phylogenetic tree and the graph. 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 incorrect?
Their hypothesis was incorrect; the graph clearly shows three distinct peaks occurring in the same wave.
Their hypothesis was still supported; each of these three groups has a different height peak.
Their hypothesis was incorrect; all three groups are rooted in the same phylogenetic tree but caused three distinct peaks in the same wave.
Their hypothesis was still supported; these three groups arose along different lineages but emerged to cause illness during the same wave.
Answer: D

34. One variant in the green groups (Groups 1, 3, and 6) 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?
Yes, it was effective; the peaks after 2009 were lower than the peaks recorded in 2009.
No, it was not effective; there were still a large number of isolates collected later in the pandemic.
No, it was not effective; there was still a measurable number of viral isolates from Groups 1, 3, and 6.
Yes, it was effective; the green line never reaches 100 on the y-axis.
Answer: D

35. One variant in the green groups (Groups 1, 3, and 6) 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?
Yes, it was effective; the peaks after 2009 were lower than the peaks recorded in 2009.
No, it was not effective; there were still a large number of isolates collected later in the pandemic.
No, it was not effective; there was still a measurable number of viral isolates from Groups 1, 3, and 6.
Yes, it was effective; the green line never reaches on the y-axis.
Answer: D