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.
-Based on the passage, which of the following viruses does NOT have an outer phospholipid bilayer?

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.
-Based on the passage, which of the following viruses does NOT have an outer phospholipid bilayer?

Quizplus · Accepted Answer

11ecba2d_0fe1_bf34_a3bf_5b29b5fd3179_MD0008_00 All viruses contain a protective protein coat, called the capsid, composed of individual capsomere subunits. Viruses that have an additional phospholipid bilayer surrounding the capsid are considered enveloped viruses. Derived from the cell membrane of host cells, the envelope helps the virus evade the immune system and contains envelope proteins required for cellular entry. However, enveloped viruses are sensitive to heat, detergents, and changes in moisture. In contrast, non-enveloped or naked viruses have only a capsid as a protective outer layer and are more resistant to heat, detergents, and changes in moisture. In the passage, researchers determined whether hepatitis viruses were enveloped or non-enveloped by exposing each virus to fluorescent antibodies designed to bind viral capsid proteins directly. Therefore, depending on the presence or absence of fluorescence, researchers would be able to determine whether the virus is non-enveloped or enveloped, respectively. The fluorescence assay revealed that capsid proteins were detected only in media containing HAV or HEV. Because the antibodies were able to bind directly to the capsid proteins of both viruses, it can be determined that HAV and HEV are non-enveloped viruses (ie, they do not have a phospholipid bilayer enveloping the capsid). (Choices A, B and D) The absence of fluorescence in media containing HBV, HCV, or HDV indicates that these viruses are enveloped viruses, meaning that their capsid proteins are covered by a protective phospholipid bilayer and cannot be bound by the antibody used by the researchers. Educational objective: All viruses contain a protective protein coat known as the capsid. Viruses that contain only a capsid as an outer layer are known as non-enveloped or naked viruses, and are able to survive in harsh conditions. Viruses with a phospholipid bilayer surrounding the viral capsid are referred to as enveloped viruses; these are more susceptible to changes in environmental conditions.