Microbiology Chapter 6 Part 2 HW

Order the terms to list the steps from HIV retroviral genome replication to protein synthesis. 1) Reverse transcriptase 2) RNA polymerase II transcription 3) dsDNA genome 4) (+) ssRNA genome 5) Integration into host genome 6) Translation of viral proteins by host ribosomes

4 > 1 > 3 > 5 > 2 > 6 You have correctly identified the HIV retroviral genome as (+) ssRNA and correctly listed the steps of genome replication and protein synthesis in the host cell.

A prophage is a Choose one: A. phage genome integrated into a host genome. B. circular phage genome that promotes cell lysis. C. bacterial virus particle that has not yet infected a cell. D. virus that promotes tumor growth in plants.

A Lysogenic viruses can integrate into the host genome to form a prophage.

Viruses express tissue tropism and host specificity. In particular, the avian influenza strain H5N1 has rare incidences in humans due to the reduced distribution of alpha-2,3 sialic acids in the lower respiratory tract. As a consequence, when the H5N1 strain does infect a human, the disease is very severe due to the risk of pneumonia. In contrast, human influenza strains (H1N1, among others) attach to alpha-2,6 sialic acids, which are readily expressed in the upper and lower respiratory tract. Which of the following would not be true if a mutation were to allow the H5N1 strain to attach to alpha-2,6 sialic acids? Choose one: A. The avian influenza strain could be transmitted directly from birds to humans. B. The avian influenza strain could be transmitted easily from human to human. C. The avian influenza strain would only infect the lower respiratory tract of humans. D. An epidemic would likely ensue due to the lack of immunity to the new avian influenza strain.

C If the avian influenza strain were adapted to bind to alpha-2,6 sialic acids, it would be capable of infecting the respiratory tract, similar to the seasonal human influenza strains, but without the afforded years of immunity to circulating strains in the human population.

The temperate phage lambda can undergo two life cycles depending on the environmental cues. During which cycle does phage lambda form a prophage? Choose one: A. slow-release cycle B. lytic cycle C. lysogeny D. burst cycle

C The prophage is formed after the phage DNA is inserted into the bacterial genome.

Temperate bacteriophages can undergo two routes of infection. During _____ the phage DNA is inserted into the bacterial genome and replicated each time the bacterial cell divides. - The prophage cycle - Lysogeny - Lysis - The slow-release cycle

Lysogeny During lysogeny, the phage genome is inserted into the bacterial genome, where they coexist as long as nutrients and conditions are favorable.

HIV, which only infects humans, is considered to have a _____ host range, whereas rabies virus, which can infect a number of animals and humans, is considered to have a _____ host range. - specific - broad - narrow - dedicated

Narrow -- since HIV only infects humans, the host range is considered narrow. Broad -- a broad host range suggests that the virus can infect several species.

Match the virus with the mechanism of uncoating the viral genome. - Influenza virus - Picornavirus - Retrovirus - Papillomavirus Viral Uncoating Location - Plasma membrane - Cytosol - Endosome

Plasma Membrane: Pico Cytosol: Retro, Papillo Endosome: Influe

Phage lambda can undergo a lytic cycle or a lysogenic cycle. Rank the steps of the lytic cycle from initial onset of bacteriophage invasion until lysis. 1) Phage lyses host cell and progeny are released. 2) Linear dsDNA cyclizes to circular DNA. 3) Phage attaches to host cell and inserts genome. 4) Phage DNA is replicated and packaged into capsids. 5) Capsid proteins are synthesized.

3 > 2 > 5 > 4 > 1

A bacterial cell is infected by a phage with an RNA genome. The bacteria has not encountered this phage before. Which of the following correctly describes host defense mechanisms that can help protect the bacterial cell? Choose one: A. Neither CRISPR nor restriction endonucleases can provide defense. B. Only CRISPR can provide defense in this case. C. Both CRISPR and restriction endonucleases can provide defense. D. Only restriction endonucleases can provide defense in this case.

A Neither of these defense mechanisms will help in this example of a pathogen with an RNA genome. Restriction endonucleases only cleave double-stranded DNA. The same is true for the Cas endonuclease component of CRISPR. Furthermore, CRISPR only defends against previously encountered pathogens.

When could virions (such as T4 phage particles) be detected within an E. coli cell? Choose one: A. during the end of the lytic cycle B. during lysogeny C. during the initial infection when the phage particle enters the E. coli cell D. never, because we don't have microscopes powerful enough to detect phage particles

A When phage DNA enters a host cell, there are two different fates. The viral DNA can integrate into the host's genome to form a prophage. In this case, each time the host cell replicates, the viral DNA is replicated as well and passed along vertically to daughter cells. Alternatively, upon entry into a host cell, the viral genome can remain separate and direct the synthesis of new viral genomes and proteins, ultimately ending in lysis of the host cell and release of newly synthesized virions.

Phage lambda can undergo a lytic cycle or a lysogenic cycle where the phage DNA is integrated into the genome in the form of a prophage. In the case of lysogeny, what induces phage lambda to transition to the lytic cycle? Choose one: A. mutation B. stress C. density of phage DNA D. excision enzymes

B Stress signals such as UV damage and nutrient deprivation prompt the excision of phage lambda from the host genome.

Human papillomavirus (HPV) is a double-stranded DNA virus that enters the cytoplasm before undergoing uncoating. Although the virus is replicated by host DNA polymerase in the nucleus, viral replication is closely tied to epithelial cell differentiation. In particular, viral DNA replication is inhibited until _____ are differentiated into _____, which are ready to be shed from the epithelial layer, increasing the likelihood that HPV will be transmitted to a new host. - Endothelial cells - Tumor cells - Basal cells - Keratinocytes

Basal cells: HPC waits for the differentiation of basal cells into mature epithelial cells that are ready to be shed or sloughed off, increasing the likelihood of viral transmission. Keratinocytes: differentiation of keratinocytes, the mature form of an epithelial cell, coincides with HPV replication.

Tropism can be defined as the Choose one: A. emergence of a new type of virus. B. mechanism of entry into a host cell for bacteriophages. C. ability to infect a particular type of cell within the host. D. ability to infect a broad range of hosts.

C Tropism is defined as the ability to infect a particular type of cell within the host.

CRISPR is Choose one: A. an enzyme that cleaves DNA that is unmethylated. B. used to make DNA from RNA. C. a protein component of the capsid. D. a set of short DNA sequences that allow the bacterium to "remember" past infections.

D CRISPR stands for clustered repeated interspaced short palindromic repeats, which are found in the bacterial genome. These are homologues to phage DNA and are transcribed and used in conjunction with a Cascade protein to cleave phage DNA on infection.

Part 1: Under what condition would a temperate bacteriophage infecting Staphylococcus aureus (an aerobic bacteria commonly found on the human body) be shifted by environmental cues from lysogeny to a lytic cycle? Choose one: A. when phage-infected cells are incubated at 37°C B. when phage-infected cells are placed on nutrient-rich media C. when phage-infected cells are incubated at atmospheric levels of oxygen D. when phage-infected cells are incubated at 50°C

D High temperatures are not permissive for bacterial growth and lead to cellular stress, which would lead to a shift from lysogeny to the lytic phase.

A _____ virus cycle leads only to cell lysis, and a _____ virus cycle involves phage genome integration into the host genome. Choose one: A. temperate; lysogenic B. lysogenic; virulent C. lysogenic; lytic D. lytic; lysogenic

D Lysogenic (temperate) viruses can integrate into the host genome to form a prophage, which results in lysogeny, a condition in which the phage genome is replicated along with that of the host cells and no lysis of host cells occurs. A lytic virus reproduces as many progeny virus particles as possible once entered into host cells, which results in lysis of host cells. A lysogenic (temperate) virus could undergo lytic cycle when triggered by environmental stress.

A temperate phage is one that Choose one: A. is incapable of lysing the host cell. B. grows best at moderate temperatures. C. is restricted to infecting a single species. D. can undergo lysogeny.

D Temperate phages may embark on a pathway called lysogeny, where the phage genome integrates into the host cell genome. The viral genome is replicated along with the host cell genome. If the host cell becomes stressed, the phage may switch to a lytic life cycle.