Viruses and their Repliction (Lec 10)

Questions and Answers

Which of the following is the correct definition of a virion?

A diverse structure that varies widely in size, shape, and chemical composition

The extracellular form of a virus (correct)

A structure that allows the virus to travel from one host cell to another

A protein shell that contains the viral genome

What is the role of the capsid in a virion?

To contain the viral genome and allow for virus to travel from one host cell to the next (correct)

To arrange proteins in a precise and highly repetitive pattern

To provide a protective protein shell

To carry enzymes critical to successful infection and replication

Which type of virus contains an outer layer of protein plus lipid?

Naked virus

Enveloped virus (correct)

Bacteriophage

Rod-shaped virus

What determines the length and width of a rod-shaped virus?

The size and packaging of protein subunits Signup and view all the answers

What is the simplest number of capsomeres per face in a spherical virus with icosahedral symmetry?

3 Signup and view all the answers

What is the primary component of the envelope in enveloped viruses?

proteins Signup and view all the answers

What are the five main steps of the viral life cycle?

Attachment, entry, synthesis, assembly, release Signup and view all the answers

Which enzyme forms a small pore in the peptidoglycan of the E. coli cell wall?

Lysozyme Signup and view all the answers

What happens within a minute after T4 entry into a host cell?

Host DNA and RNA synthesis ceases Signup and view all the answers

Which proteins are encoded by the T4 genome and required for DNA replication?

Early proteins Signup and view all the answers

What happens during the middle phase of T4 infection?

Additional proteins that modify RNA polymerase are synthesized Signup and view all the answers

What is the term for the period following attachment during which infectious virions cannot be detected in the growth medium?

Eclipse Signup and view all the answers

How is the titer of infectious virions determined in a plaque assay?

By measuring the number of plaques on a lawn of host cells Signup and view all the answers

What is the term for the ability of a virus to alternate between a lytic pathway and a lysogenic pathway?

Temperate phage Signup and view all the answers

Which of the following best describes a virus?

A genetic element that can replicate only inside a living cell Signup and view all the answers

What is the size range of most viruses?

0.02 to 0.3 µm Signup and view all the answers

Which of the following is NOT a type of infection caused by viruses?

Protozoan infection Signup and view all the answers

What is the role of a host cell in virus replication?

Provide energy and metabolic intermediates for the virus Signup and view all the answers

Which of the following is NOT a characteristic of viral genomes?

They contain only two genes Signup and view all the answers

What happens during a lytic infection?

The virus redirects host metabolism to support replication and cause host cell death Signup and view all the answers

What is the consequence of a latent infection in animal cells?

Viral DNA does not replicate Signup and view all the answers

What is the consequence of a persistent infection in animal cells?

Release of virions by budding Signup and view all the answers

Where is most of Earth's genetic diversity found?

Viruses Signup and view all the answers

What is the only viral genome that is able to translate immediately upon entering the host cell?

Postitive sense RNA Signup and view all the answers

What enzyme in retrovirus allows RNA to go to DNA?

Revers Transcriptase Signup and view all the answers

In retrovirus, the flow of genetic information after infection occurs in 'reverse'; that is, is flows from:

RNA-DNA Signup and view all the answers

Which is not an infection caused by animal cell viruses?

Lysogenetic Infection Signup and view all the answers

The process where virions come from budding of cell membrane without the final result of lysis of animal host cell is called what infection?

Persistent Infection Signup and view all the answers

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.