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Questions and Answers
Which of the following is the correct definition of a virion?
What is the role of the capsid in a virion?
Which type of virus contains an outer layer of protein plus lipid?
What determines the length and width of a rod-shaped virus?
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What is the simplest number of capsomeres per face in a spherical virus with icosahedral symmetry?
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What is the primary component of the envelope in enveloped viruses?
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What are the five main steps of the viral life cycle?
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Which enzyme forms a small pore in the peptidoglycan of the E. coli cell wall?
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What happens within a minute after T4 entry into a host cell?
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Which proteins are encoded by the T4 genome and required for DNA replication?
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What happens during the middle phase of T4 infection?
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What is the term for the period following attachment during which infectious virions cannot be detected in the growth medium?
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How is the titer of infectious virions determined in a plaque assay?
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What is the term for the ability of a virus to alternate between a lytic pathway and a lysogenic pathway?
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Which of the following best describes a virus?
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What is the size range of most viruses?
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Which of the following is NOT a type of infection caused by viruses?
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What is the role of a host cell in virus replication?
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Which of the following is NOT a characteristic of viral genomes?
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What happens during a lytic infection?
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What is the consequence of a latent infection in animal cells?
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What is the consequence of a persistent infection in animal cells?
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Where is most of Earth's genetic diversity found?
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What is the only viral genome that is able to translate immediately upon entering the host cell?
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What enzyme in retrovirus allows RNA to go to DNA?
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In retrovirus, the flow of genetic information after infection occurs in 'reverse'; that is, is flows from:
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Which is not an infection caused by animal cell viruses?
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The process where virions come from budding of cell membrane without the final result of lysis of animal host cell is called what infection?
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Study Notes
Viral Structure and Composition
- A virion is a complete and infectious virus particle that consists of a genome surrounded by a protein shell called the capsid.
- The capsid plays a crucial role in protecting the viral genome and facilitating the attachment of the virus to its host cell.
Enveloped Viruses
- Enveloped viruses possess an outer layer of protein plus lipid, known as the envelope, which is acquired from the host cell membrane during budding.
Viral Shapes and Symmetry
- The length and width of a rod-shaped virus are determined by the alignment of its protein subunits.
- In a spherical virus with icosahedral symmetry, the simplest number of capsomeres per face is three.
Viral Envelope
- The primary component of the envelope in enveloped viruses is lipid bilayer, which is derived from the host cell membrane.
Viral Life Cycle
- The five main steps of the viral life cycle are: attachment, penetration, uncoating, replication, and lysis.
Bacteriophage T4
- The enzyme lysozyme forms a small pore in the peptidoglycan of the E. coli cell wall.
- Within a minute after T4 entry into a host cell, the host cell's translation machinery is shut down.
- The proteins encoded by the T4 genome and required for DNA replication are the T4 polymerase and helicase.
- During the middle phase of T4 infection, the viral DNA is replicated, and the host cell's metabolism is altered to support viral replication.
- The period following attachment during which infectious virions cannot be detected in the growth medium is known as the eclipse phase.
Plaque Assay
- The titer of infectious virions is determined in a plaque assay by counting the number of plaques formed on a lawn of host cells.
Viral Infections
- The ability of a virus to alternate between a lytic pathway and a lysogenic pathway is known as tropism.
- A virus is a small infectious agent that requires a host cell to replicate.
- The size range of most viruses is between 20-400 nanometers.
Host Cell Role
- The role of a host cell in virus replication is to provide the necessary machinery and resources for viral replication.
Viral Genomes
- One characteristic of viral genomes is that they are not capable of translating their genetic material into proteins immediately upon entering the host cell, except for the positive-sense RNA viruses.
Types of Infections
- A lytic infection results in the lysis of the host cell, whereas a latent infection in animal cells results in the integration of the viral genome into the host cell genome, allowing the virus to establish a long-term infection.
- A persistent infection in animal cells results in the continuous production of viral particles without killing the host cell.
- Plant viruses are not known to cause latent or persistent infections.
Genetic Diversity
- Most of Earth's genetic diversity is found in viruses.
Retroviruses
- The only viral genome that is able to translate immediately upon entering the host cell is the positive-sense RNA genome.
- The enzyme reverse transcriptase in retroviruses allows RNA to be converted into DNA.
- In retroviruses, the flow of genetic information after infection occurs in 'reverse', flowing from RNA to DNA.
- Chronic infections are not caused by animal cell viruses.
- The process where virions come from budding of cell membrane without the final result of lysis of the animal host cell is called a persistent infection.
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Description
Test your knowledge on the T4 bacteriophage life cycle and its interactions with E. coli cells. Learn about the lysozyme-like enzyme, DNA replication, transcription, translation, and more.