40 Questions
One classification scheme was developed in the 1970s by Nobel laureate ______.
David Baltimore
______ classification system categorizes viruses based on the type of nucleic acid genome and replication strategy of the virus.
Baltimore
Positive-strand RNA is able to be immediately translated into ______.
proteins
Negative-strand RNA is not translatable into ______; it first has to be transcribed into positive-strand RNA.
proteins
Viruses are only classified using ______, family, genus, and species.
order
The suffix for an order of viruses is ______.
-virales
The suffix for a family of viruses is ______.
-viridae
The suffix for a genus of viruses is ______.
-virus
Viruses are categorized based upon their type of ______ acid.
nucleic
The ______ virus causes the decline of the immune system, leading to immunodeficiency.
Human immunodeficiency
The ______ virus gets its name from the Latin word for 'crown', referring to the crown-like appearance of the virions.
Corona
The ______ virus was named after the Ebola River in northern Democratic Republic of the Congo.
Ebola
The ______ virus was named after Michael Anthony Epstein and Yvonne Barr, who discovered the virus.
Epstein–Barr
A virus must undergo the process of ______ to create new, infectious virions.
replication
The ______ stage of virus replication involves the release of the viral genome from the capsid.
Uncoating
The final stage of virus replication is ______, where the virions are released from the cell to continue the process of infection.
Release
Phagocytosis is a form of ______ endocytosis that is used by specialized cells to engulf entire cells.
receptor-mediated
Fusion of the viral envelope can occur at the ______ membrane or within endocytosed vesicles, such as the endosome.
cell
Clathrin-mediated ______ is used by viruses such as dengue virus, hepatitis C virus, and reovirus.
endocytosis
Caveolin-mediated ______ is used by viruses such as human papillomavirus and hepatitis B virus.
endocytosis
Fusion is a type of penetration method used by viruses such as HIV, influenza, and ______.
respiratory syncytial virus
Uncoating refers to the breakdown or removal of the ______, causing the release of the virus genome into the cell.
capsid
Rhinoviruses are taken into the cell by ______ endocytosis in clathrin-coated vesicles.
receptor-mediated
Poliovirus releases its RNA genome into the ______ through a pore in the cell membrane.
cytoplasm
Virus attachment is the binding of the virus to the host ______.
cell
Rhinovirus binds to a protein known as ______ (ICAM-1).
intercellular adhesion molecule 1
Influenza A virus strains bind to the ______ acid sugars found at the ends of cellular carbohydrate chains.
sialic
HIV initially binds to a protein known as ______ on the surface of T lymphocytes.
CD4
Penetration refers to the crossing of the ______ membrane by the virus, following attachment.
plasma
Most types of viruses use ______-mediated endocytosis to enter the cell.
clathrin
Papillomaviruses use ______-mediated endocytosis to enter the cell.
caveolae
Bulk-phase endocytosis is the process where the cell forms a vesicle that engulfs whatever molecules are present in the ______ fluid.
extracellular
Recombination occurs when the genome of an RNA virus is being replicated and the RdRp jumps from the template of one strain to the template of the other strain, creating a hybrid ______.
genome
Reassortment occurs when the genome segments of ______ viruses are mixed while being packaged into new capsids.
segmented
Viruses components must be collected at a particular site of the cell and undergo ______ to form an immature virus particle.
assembly
Most nonenveloped DNA viruses assemble their nucleocapsid in the ______, since that is the site of genome replication.
nucleus
Viruses with envelopes derived from the plasma membrane usually assemble at the ______.
plasma membrane
Maturation refers to the final changes within an immature ______.
virion
For enveloped viruses, the final step of release involves ______ from the plasma membrane.
budding
Nonenveloped viruses can also exit the cell via ______.
exocytosis
Study Notes
Virus Classification and Taxonomy
- The Baltimore classification system categorizes viruses based on the type of nucleic acid genome and replication strategy.
- Positive-strand RNA viruses can be immediately translated into proteins, while negative-strand RNA viruses must be transcribed into positive-strand RNA first.
- Viruses are classified using the taxa: order, family, genus, and species.
Taxa Used to Classify Viruses
- Order: ends in the -virales suffix, with only about half of viruses currently classified in orders (e.g., Picornavirales).
- Family: ends in the -viridae suffix, with subfamilies indicated by the -virinae suffix (e.g., Picornaviridae).
- Genus: ends in the -virus suffix (e.g., Enterovirus).
- Species: the "common name" of the virus (e.g., Rhinovirus A).
Name Origins of Viruses
- Viruses can be named after the clinical conditions they cause (e.g., Human immunodeficiency virus, Hepatitis virus).
- Viruses can be named after their properties (e.g., Coronavirus, Herpesviruses).
- Viruses can be named after their location of discovery (e.g., Ebola virus).
- Viruses can be named after people (e.g., Epstein-Barr virus).
Virus Replication
- The seven stages of virus replication are: attachment, penetration, uncoating, replication, assembly, maturation, and release.
- Attachment: the binding of the virus to the host cell, which is specific and involves the virus attachment protein and cell surface receptor.
- Penetration: the crossing of the plasma membrane by the virus, which can occur through receptor-mediated endocytosis, bulk-phase endocytosis, phagocytosis, or fusion.
Penetration Methods
- Clathrin-mediated endocytosis (e.g., dengue virus, hepatitis C virus).
- Caveolin-mediated endocytosis (e.g., human papillomavirus, hepatitis B virus).
- Fusion (e.g., HIV, influenza, respiratory syncytial virus).
Uncoating
- The breakdown or removal of the capsid, releasing the virus genome into the cell.
- Can be separated from or tightly linked with penetration.
- Examples: rhinoviruses, poliovirus.
Assembly
- The collection of virus components at a specific site of the cell and assembly into an immature virus particle.
- Can occur in the nucleus, at the plasma membrane, or at intracellular membranes.
- Examples: non-enveloped DNA viruses (e.g., assemble in the nucleus), viruses with envelopes derived from the plasma membrane.
Maturation
- The final changes within an immature virion, involving structural capsid changes.
- Example: influenza HA protein must be cleaved into two portions (HA1 and HA2) to become infectious.
Release
- The final step of virus replication, involving the exit of the mature virion from the host cell.
- Enveloped viruses can bud from the plasma membrane and undergo exocytosis to leave the cell.
- Non-enveloped viruses can exit the cell via exocytosis or lyse the cell.
- Examples: lytic viruses, which disrupt the plasma membrane and cause cell lysis.
This quiz covers the classification and replication of viruses, including the Baltimore classification system and the types of nucleic acid genome and replication strategies.
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