Exam 3: Biology

A woman carries an X-linked recessive allele for a disorder characterized by muscle degeneration but does not express this condition.  If she has multiple offspring with an unaffected man, how many of the woman's children are expected to exhibit this degenerative disorder?

Passage Each time a eukaryotic cell replicates its DNA, the telomeres at the ends of each chromosome become slightly shorter.  When telomeres reach a critically short length, the cells enter the senescent state, in which cell division ceases (Figure 1).  In humans, conditions such as hypertension, liver disease, and Alzheimer disease have been associated with the decreased telomere length and resulting senescence that occur as part of the normal aging process. Figure 1Cells that must be able to divide indefinitely (stem cells and germ cells) express an enzyme known as telomerase.  Functional telomerase consists of a protein subunit called telomerase reverse transcriptase (TERT) and a noncoding RNA subunit called telomerase RNA (TR).  Using a portion of TR as a template, telomerase extends telomeres by continuously adding the sequence 5′-TTAGGG-3′ to the ends of chromosomes.  The complement strand is then filled in by DNA polymerase.  Telomere extension allows these cells to avoid senescence.In healthy somatic cells, however, TERT transcription is generally downregulated by the absence of the oncogene c-Myc and the presence of the tumor suppressor protein WT1.  When telomerase is suppressed, the resulting critical telomere shortening has been hypothesized to prevent uncontrolled cell proliferation in adult tissues.  In cancerous somatic cells, on the other hand, increased telomerase activity is often associated with tumorigenesis.  WT1 is frequently absent and c-Myc is frequently overexpressed in these cells, leading to increased TERT expression.In addition to transcriptional control, TERT can be regulated at the post-transcriptional level.  The TERT gene consists of 16 exons and 15 introns that can be spliced into more than 20 different isoforms in humans.  Only one isoform (the active isoform) is known to extend telomeres.  However, the i2 isoform, in which intron 2 is partially included in the mature mRNA (Figure 2), has been hypothesized to downregulate residual TERT activity in somatic cells. Figure 2 Adapted from Cifuentes-rojas C, Shippen DE. Telomerase regulation. Mutat Res. 2012;730(1-2):20-7. -WT1 and c-Myc most likely alter TERT transcription levels by doing which of the following at the TERT gene promoter?

Passage Enterohemorrhagic Escherichia coli (EHEC) O157:H7 is a bacterium responsible for causing foodborne illnesses.  EHEC virulence, or the ability to cause disease, is acquired through quorum sensing, a form of bacterial cell-cell communication dependent on population density.  EHEC O157:H7 bacteria monitor population density by detecting changes in the concentration of autoinducer-3 (AI-3), an extracellular signaling molecule secreted by many bacterial species.  AI-3 generally acts on neighboring bacteria to activate the genes on the enterocyte effacement (LEE) locus.  These genes code for type III secretion proteins (EspA, EspB, EspD, Tir), which promote entry of Shiga-like toxins secreted by EHEC into host intestinal epithelial cells.  This ultimately leads to cell death, lesions, and symptoms such as bloody diarrhea and abdominal cramps.It has been reported that a mutation in S-ribosylhomocysteine lyase (LuxS), an enzyme involved in quorum sensing, may result in diminished production of AI-3.  However, researchers predict that certain peptide hormones can activate LEE gene transcription in the LuxS.  To test this hypothesis, mutant EHEC bacteria deficient in LuxS (LuxS⁻) were cultured and separately exposed to the hormones epinephrine (E), norepinephrine (NE), gastrin (G), and secretin (S) at 37°C.  Total RNA was extracted from the treated bacterial cultures, and LEE mRNA was quantified (Figure 1). Figure 1  Concentration of LEE mRNA in mutant LuxS⁻ bacteria supplemented with purified peptide hormones (Note:  C = control.)Western blot was performed to compare the presence and concentration of type III secretion proteins from wild-type (WT), LuxS⁻, and LuxS⁻ cultured in preconditioned media (PCM).  PCM was generated by culturing uninfected intestinal epithelial cells in growth media for 24 hours.  After 24 hours, the cells were removed and the PCM was used to supplement the growth of LuxS⁻ bacteria. Figure 2  Western blot results of type III secretion proteins isolated from WT, mutant LuxS⁻, and LuxS⁻ in PCM -Which of the following is most likely to be found within the cell membranes of intestinal epithelial cells?

Passage Autosomal dominant polycystic kidney disease (ADPKD) is one of the most common heterogeneous disorders, with a reported incidence of 1 in 1,000 people.  The primary pathology is the development of numerous fluid-filled renal cysts that ultimately expand and severely impair kidney function.  By age 60, approximately 50% of patients with ADPKD progress to end-stage renal disease (ESRD) and kidney failure.  Clinical complications include high blood pressure, urinary tract infections, and cysts in other organs such as the liver and pancreas.Approximately 85% of ADPKD cases are caused by mutations in the PKD1 gene, which codes for the protein polycystin-1 (PC1).  The remaining 15% of cases are caused by mutations in the PKD2 gene, which codes for the protein polycystin-2 (PC2).  The PC2 protein functions as a mechanically activated calcium (Ca²⁺) channel in ciliated renal epithelial cells.  PC1 and PC2 interact via their C-terminal cytoplasmic tails to form a heteromer that modulates intracellular calcium homeostasis.  Disruption of calcium signaling as a result of mutations in either PKD1 or PKD2 is associated with increased cell growth and cyst formation in ADPKD patients.To identify individuals with mutations in PKD1 and PKD2, researchers analyzed phenotypic and genetic data from patients with established renal disease, as shown in Table 1.Table 1  Comparison of Renal Disease Onset and Symptom Severity in Various Patient Groups Next, researchers examined how phenotypic disease severity was affected by both the position of the mutations in PKD1 (5′ or 3′ end) and the type of mutation in PKD1 or PKD2.  In Figure 1, disease severity is given as the cumulative probability of renal survival as a function of age. Figure 1  Probability of maintaining healthy kidney physiology as a function of age, analyzed by mutation type and position Adapted from Cornec-le gall E, Audrézet MP, Chen JM, et al. J Am Soc Nephrol. 2013;24(6):1006-13. -In advanced ADPKD, all of the following components of physiological homeostasis would be disrupted EXCEPT:

The diagram below shows part of the life cycle of a novel virus that infected an Escherichia coli cell. Which of the following experimental techniques can be used to detect the genetic material of this virus in the host cell?

Passage The Bloom syndrome helicase (BLM) transcript is catalytically inactive in Bloom syndrome (BS), a genetic disorder that leads to genomic instability characterized by excessive somatic recombination events.  Research studies have shown that BLM may be involved in DNA synthesis repair of stalled replication forks during replication stress (arrest).  To investigate this further, an experiment was conducted using cell lines derived from a patient with BS.  One set of cells differed only by BLM status:  PSNF5 (BLM⁺, vector with BLM cDNA transfected) and PSNG13 (BLM⁻, empty vector transfected).  Additional mutations, BLM-K695T and BLM-T99A, were studied in stable transfected cells.The nucleoside analogs iododeoxyuridine (IdU) and chlorodeoxyuridine (CldU) were used to label and track genomic regions of active replication.  Cells were initially treated with IdU for 15 minutes.  Subsequently, either 4 mM of hydroxyurea (HU) or 30 µM of aphidicolin (Aph) were used to induce replication stress for 4 hours, after which cells were treated with CldU for 85 minutes to assess replication recovery.  Cells were mounted on microscope slides, lysed to isolate chromosome fibers, and then fixed on the slides.  Sites of IdU and CldU incorporation into the growing DNA strand were then detected by immunostaining the isolated chromosome fibers with analog-specific, fluorescent-coupled antibodies.  Replication activity was visualized via microscopy and measured. Figure 1  (A) Experimental protocol and (B) fluorescent imaging of a microscope slide showing incorporation of IdU (black lines) and CldU (gray lines) into DNA fibers isolated from a group of BLM⁺ and BLM⁻ cells, with single fibers depicted in each row Figure 2  Replication fork recovery in cells expressing BLM⁺, BLM⁻, and the mutation BLM-K695T (antagonistic to wild-type) Figure 3  New sites of replication in cells expressing BLM⁺, BLM⁻, and the mutation BLM-T99A (T99 phosphorylated after replication arrest) Adapted from Davies SL, North PS, Dart A, Lakin ND, Hickson ID. Mol Cell Biol. 2004;24(3):1279-91. -The BLM peptide sequence was used to search for similar peptides in various species using an amino acid sequence homology (similarity) database.  BLM and other peptides were found to share similar amino acid sequences only in the DNA helicase domains.  The results of sequence homology with BLM are shown in the table below. Which statement best explains the role of these peptides during replicative stress in the organisms studied?

If a viral antigen were to bind to the receptors on the surface of a B lymphocyte, which of the following immune responses would NOT occur?

Passage In the central nervous system, myelin produced by oligodendrocytes (glial cells) functions as an insulating sheath surrounding certain nerve fibers.  To identify candidate genes involved in the myelination process, researchers collected oligodendrocytes from zebrafish and purified the messenger RNA (mRNA) transcripts expressed by these glial cells.  The mRNA was converted to complementary DNA (cDNA) by reverse transcriptase, and the cDNA was fluorescently labeled and assessed for hybridization on a microarray.  The expression of mRNA in other zebrafish cells was similarly measured.Transcripts detected in zebrafish oligodendrocytes at levels greater than 3 times those found in other cells were selected as candidate myelination genes.  Some of the detected genes, including plp1a, Sox10, and mbp, were previously known to be specific to oligodendrocytes, validating the procedure.  The cDNA of newly identified candidates was amplified by PCR, and the ends were digested with the restriction enzymes EcoRI and XhoI.  Genes were then ligated into the multiple cloning site (MCS) of the pSKII vector, shown in Figures 1 and 2, which had also been digested by EcoRI and XhoI. Figure 1  Overview of the pSKII vector (plasmid) Figure 2  The pSKII MCS, showing the restriction sites of several restriction enzymesTable 1 shows the functional parameters of several restriction enzymes. To confirm that the candidate genes originated in oligodendrocytes, complementary RNA (cRNA) strands were synthesized from the cloned plasmids and hybridized to fixed zebrafish sections.  One of the genes that localized to oligodendrocytes, known as cldnk, produces a 915 base pair mRNA transcript from two exons.  The cldnk gene is involved in tight junction formation and may be required for myelin sheath development around axons. -Microarrays are chips that contain hundreds of microscopic wells, each of which can detect a distinct nucleic acid.  Prior to exposure to cDNA, the wells of the microarray described in the passage most likely contained:

Passage Adeno-associated virus 2 (AAV2) is a nonpathogenic, nonenveloped DNA virus that requires helper viruses such as adenovirus (AV) or herpes simplex virus (HSV) to replicate efficiently.  Because it can transduce human cells, including quiescent (nondividing) cells, without causing disease, AAV2 is attractive as a gene therapy vector.  In clinical trials, a modified AAV2 virus has successfully treated the retinal disease Leber's congenital amaurosis as well as the blood clotting disorder hemophilia B.  AAV2 transduces cells via a multistep process, shown in Figure 1. Figure 1  Schematic showing the mechanism of transduction by AAV2Studies indicate that unlike AV and HSV, AAV2 inhibits pathways other than the endosomal pathway, such as trafficking to the Golgi, increasing the percentage of invading virus particles that arrive at the nucleus. Adapted from Xiao PJ, Samulski RJ. Cytoplasmic trafficking, endosomal escape, and perinuclear accumulation of adeno-associated virus type 2 particles are facilitated by microtubule network. J Virol. 2012;86(19):10462-73. -What is the fate of the virus particles that fail to escape the acidified endosome in Figure 1, Step 6?

Passage Each time a eukaryotic cell replicates its DNA, the telomeres at the ends of each chromosome become slightly shorter.  When telomeres reach a critically short length, the cells enter the senescent state, in which cell division ceases (Figure 1).  In humans, conditions such as hypertension, liver disease, and Alzheimer disease have been associated with the decreased telomere length and resulting senescence that occur as part of the normal aging process. Figure 1Cells that must be able to divide indefinitely (stem cells and germ cells) express an enzyme known as telomerase.  Functional telomerase consists of a protein subunit called telomerase reverse transcriptase (TERT) and a noncoding RNA subunit called telomerase RNA (TR).  Using a portion of TR as a template, telomerase extends telomeres by continuously adding the sequence 5′-TTAGGG-3′ to the ends of chromosomes.  The complement strand is then filled in by DNA polymerase.  Telomere extension allows these cells to avoid senescence.In healthy somatic cells, however, TERT transcription is generally downregulated by the absence of the oncogene c-Myc and the presence of the tumor suppressor protein WT1.  When telomerase is suppressed, the resulting critical telomere shortening has been hypothesized to prevent uncontrolled cell proliferation in adult tissues.  In cancerous somatic cells, on the other hand, increased telomerase activity is often associated with tumorigenesis.  WT1 is frequently absent and c-Myc is frequently overexpressed in these cells, leading to increased TERT expression.In addition to transcriptional control, TERT can be regulated at the post-transcriptional level.  The TERT gene consists of 16 exons and 15 introns that can be spliced into more than 20 different isoforms in humans.  Only one isoform (the active isoform) is known to extend telomeres.  However, the i2 isoform, in which intron 2 is partially included in the mature mRNA (Figure 2), has been hypothesized to downregulate residual TERT activity in somatic cells. Figure 2 Adapted from Cifuentes-rojas C, Shippen DE. Telomerase regulation. Mutat Res. 2012;730(1-2):20-7. -Based on the sequence that telomerase adds to the ends of chromosomes, the template portion of TR most likely contains which of the following sequences?

Passage Enterohemorrhagic Escherichia coli (EHEC) O157:H7 is a bacterium responsible for causing foodborne illnesses.  EHEC virulence, or the ability to cause disease, is acquired through quorum sensing, a form of bacterial cell-cell communication dependent on population density.  EHEC O157:H7 bacteria monitor population density by detecting changes in the concentration of autoinducer-3 (AI-3), an extracellular signaling molecule secreted by many bacterial species.  AI-3 generally acts on neighboring bacteria to activate the genes on the enterocyte effacement (LEE) locus.  These genes code for type III secretion proteins (EspA, EspB, EspD, Tir), which promote entry of Shiga-like toxins secreted by EHEC into host intestinal epithelial cells.  This ultimately leads to cell death, lesions, and symptoms such as bloody diarrhea and abdominal cramps.It has been reported that a mutation in S-ribosylhomocysteine lyase (LuxS), an enzyme involved in quorum sensing, may result in diminished production of AI-3.  However, researchers predict that certain peptide hormones can activate LEE gene transcription in the LuxS.  To test this hypothesis, mutant EHEC bacteria deficient in LuxS (LuxS⁻) were cultured and separately exposed to the hormones epinephrine (E), norepinephrine (NE), gastrin (G), and secretin (S) at 37°C.  Total RNA was extracted from the treated bacterial cultures, and LEE mRNA was quantified (Figure 1). Figure 1  Concentration of LEE mRNA in mutant LuxS⁻ bacteria supplemented with purified peptide hormones (Note:  C = control.)Western blot was performed to compare the presence and concentration of type III secretion proteins from wild-type (WT), LuxS⁻, and LuxS⁻ cultured in preconditioned media (PCM).  PCM was generated by culturing uninfected intestinal epithelial cells in growth media for 24 hours.  After 24 hours, the cells were removed and the PCM was used to supplement the growth of LuxS⁻ bacteria. Figure 2  Western blot results of type III secretion proteins isolated from WT, mutant LuxS⁻, and LuxS⁻ in PCM -E. coli K-12, a normal bacterial strain of the human microbiota, is able to cause disease by inducing enterocyte lesions after it is grown in media with EHEC bacteria that contain the F factor plasmid.  What process most likely granted virulence to E. coli K-12?

Passage Adeno-associated virus 2 (AAV2) is a nonpathogenic, nonenveloped DNA virus that requires helper viruses such as adenovirus (AV) or herpes simplex virus (HSV) to replicate efficiently.  Because it can transduce human cells, including quiescent (nondividing) cells, without causing disease, AAV2 is attractive as a gene therapy vector.  In clinical trials, a modified AAV2 virus has successfully treated the retinal disease Leber's congenital amaurosis as well as the blood clotting disorder hemophilia B.  AAV2 transduces cells via a multistep process, shown in Figure 1. Figure 1  Schematic showing the mechanism of transduction by AAV2Studies indicate that unlike AV and HSV, AAV2 inhibits pathways other than the endosomal pathway, such as trafficking to the Golgi, increasing the percentage of invading virus particles that arrive at the nucleus. Adapted from Xiao PJ, Samulski RJ. Cytoplasmic trafficking, endosomal escape, and perinuclear accumulation of adeno-associated virus type 2 particles are facilitated by microtubule network. J Virol. 2012;86(19):10462-73. -As it matures, the endosomal lumen becomes acidified relative to the cytosol.  Protons from the cytosol most likely enter the endosomal lumen by which of the following processes?

Passage Autosomal dominant polycystic kidney disease (ADPKD) is one of the most common heterogeneous disorders, with a reported incidence of 1 in 1,000 people.  The primary pathology is the development of numerous fluid-filled renal cysts that ultimately expand and severely impair kidney function.  By age 60, approximately 50% of patients with ADPKD progress to end-stage renal disease (ESRD) and kidney failure.  Clinical complications include high blood pressure, urinary tract infections, and cysts in other organs such as the liver and pancreas.Approximately 85% of ADPKD cases are caused by mutations in the PKD1 gene, which codes for the protein polycystin-1 (PC1).  The remaining 15% of cases are caused by mutations in the PKD2 gene, which codes for the protein polycystin-2 (PC2).  The PC2 protein functions as a mechanically activated calcium (Ca²⁺) channel in ciliated renal epithelial cells.  PC1 and PC2 interact via their C-terminal cytoplasmic tails to form a heteromer that modulates intracellular calcium homeostasis.  Disruption of calcium signaling as a result of mutations in either PKD1 or PKD2 is associated with increased cell growth and cyst formation in ADPKD patients.To identify individuals with mutations in PKD1 and PKD2, researchers analyzed phenotypic and genetic data from patients with established renal disease, as shown in Table 1.Table 1  Comparison of Renal Disease Onset and Symptom Severity in Various Patient Groups Next, researchers examined how phenotypic disease severity was affected by both the position of the mutations in PKD1 (5′ or 3′ end) and the type of mutation in PKD1 or PKD2.  In Figure 1, disease severity is given as the cumulative probability of renal survival as a function of age. Figure 1  Probability of maintaining healthy kidney physiology as a function of age, analyzed by mutation type and position Adapted from Cornec-le gall E, Audrézet MP, Chen JM, et al. J Am Soc Nephrol. 2013;24(6):1006-13. -A woman whose father is heterozygous for an ADPKD-causing mutation in PKD1 and whose mother is unaffected has a child with a man with no family history of ADPKD.  What is the percent chance that their first child will have ADPKD?  (Note: Assume the woman's ADPKD status is unknown.)

Passage The fruit fly Drosophila melanogaster is frequently used as a model system to investigate neurological disorders.  The genes Abl, Enabled (Ena), and receptor protein tyrosine phosphatase (PTP) are involved in axonal guidance during neuronal development and are all believed to operate in the same pathway.  To investigate interactions between PTP and either Ena or Abl, fly lines were developed in which mutations of each gene were easily identifiable by eye characteristics.  In flies that would normally have white eyes, a dominant mutation that inactivates PTP results in red and white eyes; a dominant Ena mutation yields orange eyes (or red and orange if the PTP and Ena mutations are both present); and a dominant Abl mutation yields elongated eyes.  Using these fly lines, the following experiments were conducted.Experiment 1Females heterozygous for PTP (eePp) were crossed with males heterozygous for Ena (Eepp).  F1 generation males and females, each with red and orange eyes, were then selected and crossed with each other to produce an F2 generation.  Flies with two mutant Ena alleles (EE), as well as those with two mutant PTP alleles and at least one mutant Ena allele (EePP), did not survive past the larval stage.Experiment 2PTP and Abl are located on the same chromosome.  Females with the PTP mutation on one copy of the chromosome and the Abl mutation on the other copy were crossed with wild-type males.  In Drosophila, recombination occurs only in female gametes.  Progeny with parental and recombinant genotypes are shown in Table 1.  F1 males with red and white elongated eyes were then crossed with homozygous PTP mutant females.  This produced an F2 generation in which 50% of both male and female progeny had elongated eyes.Table 1  Phenotypes of 500 F1 Flies Like humans, male flies have a single X chromosome, whereas females have two X chromosomes.  Unlike humans, female Drosophila can store sperm and fertilize multiple eggs over the course of several days after a single mating.  Researchers ensured that females were virgins prior to setting up each cross to avoid contamination. Adapted from Song JK, Giniger E, Desai CJ. The receptor protein tyrosine phosphatase PTP69D antagonizes Abl tyrosine kinase to guide axons in Drosophila. Mech Dev. 2008;125(3-4):247-56. -A female virgin heterozygous for both PTP and Ena (EePp) mated with a single, unknown male that was produced by the parental cross described in Experiment 1.  If 25% of the resulting progeny died in the larval stage, the genotype of the male was most likely:

Passage Quantitative fluorescence recovery after photobleaching (FRAP) is used to study the movement of molecules in live cells.  During FRAP, the fluorescence of a green fluorescent protein (GFP)-tagged molecule is first measured and then photodestroyed in targeted cell regions.  Researchers then assess the time course for fluorescence recovery, which is an indicator of molecular mobility of the GFP-tagged protein into the photodestroyed region.  The average time required to recover 80% of the pre-bleach fluorescence of protein histone 1 (H1) fused to GFP (H1-GFP) in the photodestroyed region is given as t80.FRAP was used to analyze the mobility of the architectural H1 alone and in the presence of high-mobility group (HMG) proteins.  HMG proteins are dynamic modifiers that have been shown to have opposite effects but similar binding sites on chromatin structure. Figure 1  Unique chromatin binding motifs of HMG proteinsDuring analysis, HMGA1 and HMGB1 were microinjected into the cytoplasm of mouse embryonic fibroblast cells expressing H1-GFP.  FRAP was performed on euchromatin and heterochromatin.  Euchromatin and heterochromatin domains were identified as regions weakly and strongly stained by H1-GFP, respectively.  The relative intensity of H1-GFP fluorescence in euchromatin and heterochromatin of uninjected and injected cells was assessed, and t80 results are shown in Table 1.Table 1  Effect of HMGB1 and HMGA1 on H1-GFP Mobility Adapted from Catez F, Yang H, Tracey KJ, Reeves R, Misteli T, Bustin M. Network of dynamic interactions between histone H1 and high-mobility-group proteins in chromatin. Mol Cell Biol. 2004;24(10):4321-8. -If mutant HMGN2 proteins were unable to bind their substrate and then erroneously mobilize to nucleoli, these proteins would be found in the sites of:

A male African clawed frog (Xenopus laevis) and a female Western clawed frog (Xenopus tropicalis) mate and produce multiple hybrid embryos that die early in development.  Given this, death of the hybrid embryo is most likely caused by:

Passage Within the Actinopterygii (bony fish) lineage, marine teleosts (bony fish with mobile jaws) live in an aquatic environment where there is a higher external concentration of salt and a lower concentration of water relative to the internal concentrations.  Owing to these conditions, salt ions tend to diffuse into the teleost through its skin, whereas water molecules within the organism osmotically traverse the opposite path.Irrespective of lineage, many fish species actively assess their environment and regulate their internal concentration of fluids and electrolytes via a homeostatic process known as osmoregulation.  Teleosts with either glomerular kidneys (eg, eels, sculpin) or aglomerular kidneys that are purely tubular (eg, goosefish, toadfish) have served as experimental subjects for the study of marine teleost osmoregulation.  Analyzing the ionic (ie, Na⁺, Cl⁻, Mg²⁺, SO₄²⁻) concentration of intestinal fluids, urine, and plasma in each species led to the discovery that the renal tubule of the goosefish has both excretory and reabsorptive functions.Scientists have concluded that marine teleost osmoregulation involves the ingestion of seawater, retrieval of NaCl and water from the intestine, and primary excretion of divalent ions via urine and monovalent ions through the gills (thin barriers between the organism's blood and the aquatic environment).In an experiment to further study osmoregulatory mechanisms, researchers emptied the gut of an eel and sealed the anus to prevent fluid loss.  The eel was transported into seawater that had been treated with the volume marker phenol red.  After 20 hours, the eel's gut contained 2.3 mL of fluid but showed a phenol red concentration equivalent to 12.3 mL of ingested seawater.  Researchers found that the eel lost 2.3 g of weight due to urine output.  They ultimately reported that the eel had lost all the seawater it absorbed through the gut via various mechanisms. -Which of the following conclusions about the eel can be made based on the experiment in the passage?  (Note: Water density is 1 g/mL.)

The processes of spermatogenesis and oogenesis in humans are similar in that they both:

One function of the bulbourethral glands is to:

Passage Viruses are known as obligate intracellular parasites because they cannot reproduce independently (outside of a host cell).  Viral genomes (RNA or DNA) are enclosed by a protein shell known as the capsid.  Some viruses, known as enveloped viruses, have an additional phospholipid bilayer that fully envelops the capsid.  Viruses that lack this outermost phospholipid covering are labeled non-enveloped.  The entry of either enveloped or nonenveloped viruses into a host cell enables the production of viral proteins and the subsequent assembly of viral progeny.Immune cells (B and T cells) protect host organisms against viral infections by recognizing viral particles (antigens) as foreign.  In response to the recognition of foreign particles, antigen-presenting cells display cleaved antigens (also known as antigen fragments) on their surface, which enable the activation of other immune cells that stimulate an immune response, including the production of neutralizing antibodies.An example of an infectious disease is viral hepatitis (inflammation of the liver), which can be caused by any one of five distinct hepatitis viruses (A-E) that infect hepatocytes (liver cells).  HAV, HCV, and HEV contain positive-sense, single-stranded RNA (+ssRNA) as genetic material.  In contrast, HBV has a partially double-stranded circular DNA genome.  HDV is unique because it has a negative-sense, single-stranded RNA (−ssRNA) genome.Researchers hypothesized that synthetic antibodies could be used to treat viral hepatitis in patients with compromised immune systems.  Fluorescent antibodies, designed to bind the capsid proteins of the five hepatitis viruses, were added to separate wells containing each type of virus.  The fluorescence assay that was performed detected only bound antibodies in media with HAV or HEV. Adapted from Shin EC, Sung PS, Park SH. Immune responses and immunopathology in acute and chronic viral hepatitis. Nat Rev Immunol. 2016;16(8):509-23. -Researchers perform an experiment in which they infect wild-type mice with either HBV or HEV and subsequently treat them with a drug that inhibits their cellular RNA polymerase activity.  Based on the passage, administering this drug to mice infected with either HBV or HEV would result in:Decreased viral load in HBV-infected miceDecreased viral load in HEV-infected miceReduced number of viral fragments displayed by antigen-presenting cells in HBV-infected mice