Mastering Biology Chapter 19 HW

viruses & host cell

- RNA - DNA - protein

Which statements about viruses are true?

- The capsid enters the host cell if the virus is enveloped - A retrovirus contains RNA. - HIV contains reverse transcrpitase - Enveloped viruses bud from the host cell

How do prions differ from viruses?

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

viruses only

- capsid - envelope with glycoproteins - capsomere(core protein)

lytic cycle

- the host is destroyed - the cell is lysed (broken open) - new phages are assembledfrom viral DNA and proteins

lysogenic cycle

- the viral DNA integrates intothe chromosome of the host cell - the cell reproduces normally

Which of these binds to receptor molecules on the host cell membrane?

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

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. Referring to the phylogenetic tree in Figure 1, which variant is more closely related to A/Taiwan1018/2011 in group 9 (brown): A/Taiwan/552/2011 or A/Taiwan/8542/2009? (For help reading the phylogenetic tree, see the hint.)

A/Taiwan/552/2011; variants 1018/2011 and 552/2011 share a more recent common ancestor than is shared with variant 8542/2009. *You can see from the tree that A/Taiwan1018/2011 and A/Taiwan/552/2011 share a more recent common ancestor than A/Taiwan1018/2011 and A/Taiwan/8542/2009 do. The branch length from the node connecting the former pair is shorter than the branch length from the node connecting the latter pair.

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 these is reverse transcriptase?

C

Which of these is the viral genome?

E

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. Select Figure 2 from the drop-down menu above the phylogenetic tree (Figure 2). 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. Which group of variants was the earliest to cause H1N1 flu in over 100 patients in Taiwan?

Group 7 (black line)

What is the function of reverse transcriptase?

It catalyzes the formation of DNA from an RNA template.

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.

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 groups experienced a higher mutation rate than others.

How do prions, which are misfolded proteins, infect organisms? See Concept 19.3 (Page)

Prions enter brain cells and cause normal forms of the protein to refold into the prion form. *Prions are a misfolded version of a protein normally found in the brain. When prions come into close proximity with the normal proteins, they cause them 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? See Concept 19.3 (Page)

The viral infection was acquired by vertical transmission. *"Vertical transmission" refers to the inheritance of a viral infection from a parent.

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? Explain your answer.

Their hypothesis was still supported; these three groups arose along different lineages but emerged to cause illness during the same wave. *All three groups had variants that were genetically distinct from the variants that caused the earlier infection waves. These three groups just happened to cause serious infection at the same time.

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.

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? Why or why not?

Yes, it was effective; the green line never reaches 100 on the y-axis. *The green line represents viral isolates from Groups 1, 3, and 6. Because that line never reaches a high peak, you can conclude that the vaccine was effective against those three groups.

The H1N1 2009 outbreak is considered to have been which of the following? See Concept 19.3 (Page)

a pandemic

The nucleic acid of a virus particle is enclosed in a protein coat. What is it called? See Concept 19.1 (Page)

capsid

What is the source of a viral envelope?

host cell membrane

Cycle A is the _____ cycle and cycle B is the _____ cycle.

lytic ... lysogenic *The lytic cycle concludes with rupture of the host cell. The lysogenic cycle involves replication of viral DNA along with replication of the host.

Double-stranded viral DNA is incorporated into a host cell as a _____.

provirus

What enzyme is responsible for the process seen here?

reverse transcriptase

HIV uses which of the following processes to synthesize a DNA strand using its RNA genome as a template? See Concept 19.2 (Page)

reverse transcription *Retroviruses are equipped with an enzyme called reverse transcriptase, which makes a DNA copy of an RNA template, providing information flow from RNA to DNA

host cell only

ribosome

The lytic cycle of bacteriophage infection ends with the _____.

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

The genetic material of HIV consists of _____.

single-stranded RNA

As a result of the lytic cycle, _____.

the host cell's DNA is destroyed

What is the most effective way to stop viral infections? See Concept 19.3 (Page)

vaccines *Vaccines stimulate the immune system to recognize and effectively fight off invading viruses. They have proven to be the most effective weapon against viruses.

In the lysogenic cycle _____.

viral DNA is replicated along with host DNA

lytic & lysogenic cycle

viral genes are replicated

The pointer is indicating the _____.

viral protein coat