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.
-Physicians researching a global hepatitis outbreak discover a new strain of hepatitis (HXV) by analyzing chromosomal DNA of patient's liver cells. They found that HXV has a +ssRNA genome and replicates through DNA intermediates. What characteristic best describes the new hepatitis virus?

Question

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.
-Physicians researching a global hepatitis outbreak discover a new strain of hepatitis (HXV) by analyzing chromosomal DNA of patient's liver cells.  They found that HXV has a +ssRNA genome and replicates through DNA intermediates.  What characteristic best describes the new hepatitis virus?

Quizplus · Accepted Answer

11ecba2d_0fe3_e218_a3bf_5d1d7b3426df_MD0008_00 The newly discovered hepatitis strain, HXV, was identified while analyzing chromosomal DNA of liver (host) cells. This indicates that the virus is a retrovirus because it integrated with the host genome (DNA). Retroviruses are unique in that they are enveloped and carry two identical +ssRNA molecules. Successful viral replication of HXV depends on enzymes that allow its viral genome (RNA) to enter the nucleus and integrate with the host genome (DNA). Retroviruses enter host cells through endocytosis, which allows the capsid and envelope to uncoat (disassemble). Uncoating releases the viral genetic material inside the host cell. RNA viruses such as HXV must convert their genomes (+ssRNA) into double-stranded DNA (dsDNA) using reverse transcriptase (RNA-dependent DNA polymerase activity) before integration into the host genome can occur. Once integrated, the viral genome is replicated along with the host cell's own DNA as a lysogenic provirus. Consequently, the original cell containing the integrated viral genome will divide and produce descendants that are also infected. (Choice A) Retroviruses such as HXV can integrate viral dsDNA (not +ssRNA) into the host genome. (Choice C) Because the genome of HXV is +ssRNA, the synthesis of a complementary strand would produce a −ssRNA molecule with no usable functions; therefore, it neither codes for proteins nor integrates into the host genome. In addition, if the viral ssRNA strands were to hybridize and form a dsRNA molecule, it also could not integrate into the host genome because viral dsRNA has to be converted into dsDNA for incorporation into the host genome. (Choice D) According to the passage, viruses are obligate intracellular parasites, meaning they cannot replicate outside a host cell. Independent replication cannot occur because viruses lack the ability (resources and enzymes) to produce their own proteins. Educational objective: Retroviruses are enveloped, positive-sense, single-stranded RNA viruses that convert their RNA genomes into double-stranded DNA using the enzyme reverse transcriptase. During their lysogenic cycles, retroviruses enter the nucleus and integrate their reversed transcribed DNA with the host genome.