Virology: Understanding Virus Life Cycle and Assembly

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Questions and Answers

What is the purpose of proteolytic cleavage in the assembly of non-enveloped animal viruses?

To transcribe mRNA from viral DNA

To synthesize viral genomes

To induce the final conformation in the capsid proteins (correct)

To replicate viral DNA

Where do DNA viruses primarily replicate?

In the endoplasmic reticulum

In the nucleus (correct)

In the mitochondria

In the cytoplasm

What is the function of 'early' proteins in the virus life cycle?

To translated into non-structural proteins (correct)

To replicate the viral genome

To synthesize viral RNA

To build the capsid proteins

What is the role of receptors in the attachment stage of the virus life cycle?

To define and limit the host species and cell type infected Signup and view all the answers

What is the result of amplification of the viral genome and viral proteins?

Production of new viral genomes for incorporation into progeny virions Signup and view all the answers

What is the purpose of the capsid proteins in the virus life cycle?

To build the virion structure Signup and view all the answers

What is the difference between DNA and RNA viruses in terms of replication?

DNA viruses replicate mainly in the nucleus, while RNA viruses replicate mainly in the cytoplasm Signup and view all the answers

What is the result of the spontaneous assembly of the capsid proteins around the nucleic acid genome?

Formation of the virus particle Signup and view all the answers

What is the mechanism by which enveloped viruses are released from the host cell?

Budding from the cell surface Signup and view all the answers

What is the function of the RdRp enzyme in negative sense viruses?

To copy the negative sense genome into mRNA Signup and view all the answers

What is the process by which some enveloped viruses enter the host cell?

Endocytosis Signup and view all the answers

What is the term for the release of viral genome from its protective capsid?

Uncoating Signup and view all the answers

What is the mechanism by which some enveloped viruses utilize to exit the host cell?

The cellular secretory pathway Signup and view all the answers

What is the role of viral envelope glycoproteins in enveloped viruses?

To accumulate in the plasma membrane during budding Signup and view all the answers

What is the term for the process by which viruses use two different receptors on the same host cell for initial attachment and closer attachment?

Attachment/Adsorption Signup and view all the answers

What is the function of the capsid proteins in enveloped viruses?

To condense adjacent to the cell membrane during budding Signup and view all the answers

Study Notes

Virus Life Cycle

Virus life cycle consists of several stages: attachment/adsorption, penetration and uncoating, nucleic acid replication, viral protein synthesis, assembly and release.

Attachment/Adsorption

Viral attachment protein specifically binds to a receptor on the cell plasma membrane.
Receptors can be proteins (e.g. ICAM-1 for most rhinoviruses, ACE2 for SARS-CoV-2) or carbohydrates (sialic acid for influenza virus).
Receptors are not for the cell's benefit but are involved in normal processes, and viruses have evolved to utilize them to gain entry.

Penetration and Uncoating

After attachment, the coat of enveloped viruses may fuse with the host cell membrane and release the virus nucleocapsid into the host cytoplasm.
Other viruses may enter the cell by a process of endocytosis, which involves invagination of the cell membrane to form vesicles in the cell cytoplasm.
Uncoating refers to the release of the viral genome from its protective capsid to enable the nucleic acid to be transported within the cell and transcribed to form new progeny virions.

Nucleic Acid Replication

DNA viruses replicate mainly in the nucleus, while RNA viruses replicate mainly in the cytoplasm.
Nucleic acid replication produces new viral genomes for incorporation into progeny virions.
Messenger RNA (mRNA) is transcribed from viral DNA (or formed directly from some RNA viruses) and codes for viral proteins that are translated by the host cell.

Viral Protein Synthesis

"Early" proteins are usually non-structural (e.g. DNA or RNA polymerase) and later proteins are structural, e.g. capsid proteins, building blocks of the virion.
RNA polymerase is a special enzyme used by negative sense viruses, such as influenza virus, to copy its negative sense genome into mRNA.

Assembly and Release

Non-enveloped animal viruses have an icosahedral structure, which can be formed through spontaneous assembly of the capsid proteins around the nucleic acid genome.
Virions accumulate in the cytoplasm or nucleus and are only released when the cell eventually lyses.
Enveloped viruses release may take place by budding from the cell surface, where patches of viral envelope glycoproteins accumulate in the plasma membrane, and the capsid proteins and nucleic acid condense directly adjacent to the cell membrane.

Enveloped Viruses

Some enveloped viruses utilize the cellular secretory pathway to exit the cell, where virus particles bud into Golgi-derived vesicles and are released to the outside of the cell when the transport vesicle fuses with the cell membrane.
Viral membrane fusion is used by some viruses to induce fusion of the viral envelope and the cell membrane.

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Description

This quiz covers the different stages of the virus life cycle, including key components, unique enzymes, cell organelles, and host vs virus factors. It also explores methods used to study viruses and their effects on cells, as well as virus assembly and release.