Viral Genetics and Mutations

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Questions and Answers

Which of the following processes are responsible for mutations in viral DNA and RNA?

Basesubstitution

Deletion

Frame shift

All of the above (correct)

What is the most important practical application of mutations in viral genetics?

Production of vaccines containing live, attenuated viruses.

DNA viruses utilize the host cell's DNA synthetic machinery, benefiting from their proofreading and error-correcting mechanisms.

True

RNA viruses possess proofreading capacity, reducing the frequency of mutations during replication.

False Signup and view all the answers

What is the term used to describe the origination of genetic variants due to mutational change in RNA viruses?

Antigenic drift Signup and view all the answers

What type of virus variant is characterized by an altered surface protein, often making it resistant to pre-existing antibodies?

Antigenic variant Signup and view all the answers

What are the viruses that are insensitive to antiviral drugs, often due to modifications in their target viral enzymes?

Drug-resistant mutants Signup and view all the answers

What are defective interfering particles, and what is their unusual property?

Defective interfering particles are viruses with deletions that prevent their own replication unless a helper virus provides the missing functions. They can interfere with the growth of normal viruses. Signup and view all the answers

What are the three primary phenomena that can occur when two genetically distinct viruses infect the same host cell?

Recombination, reassortment, and complementation. Signup and view all the answers

Describe the process of recombination in viral genetics.

Recombination is the exchange of genetic material between two viruses through crossing over, resulting in progeny viruses with combinations of traits not found in either parent. Signup and view all the answers

What type of viruses does reassortment typically occur in, and why?

Viruses with segmented RNA genomes like influenza viruses, because the segments can be exchanged during replication. Signup and view all the answers

What happens during complementation in viral infection?

A non-defective virus provides a functional protein to complement a defective virus that lacks that protein, allowing the defective virus to replicate. Signup and view all the answers

What happens during phenotypic mixing?

The capsid proteins of progeny viruses are a mixture of proteins from both parental viruses, potentially affecting their cellular tropism. Signup and view all the answers

Explain the process of phenotypic masking (transcapsidation).

The capsid proteins of one parental virus encapsulate the genome of a second parental virus, potentially altering the cellular tropism of the progeny viruses. Signup and view all the answers

What are pseudotypes, and how are they used?

Pseudotypes are artificial viruses composed of the nucleocapsid of one virus and the envelope of another, often used to study immune responses to viruses like HIV. Signup and view all the answers

What is interference in viral infection?

Interference occurs when one virus inhibits the replication of another virus in a host cell, often mediated by interferon. Signup and view all the answers

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Study Notes

Viral Genetics

The study of viral genetics encompasses two areas:
- Mutations and their effects on replication and pathogenesis
- Interaction of two genetically distinct viruses infecting the same cell

Mutations

Mutations in viral DNA and RNA occur through base substitution, deletion, and frameshift mutations.
Mutations are crucial in vaccine development, as attenuated mutants (weakened but still antigenically similar) are used to develop vaccines. These vaccines do not cause disease but induce immunity.
DNA viruses leverage host cell machinery, benefiting from proofreading and error correction mechanisms, leading to fewer mutations.
RNA viruses undergo more mutations due to the lack of proofreading capabilities in their polymerases. This high mutation rate allows them to rapidly adapt to changing environments. This adaptability is referred to as antigenic drift.
Two other types of mutants exist:
- Antigenic variants: These have altered surface proteins, making them resistant to pre-existing antibodies. They can lead to disease outbreaks.
- Drug-resistant mutants: These are insensitive to antiviral drugs as their viral targets have been modified.
- Defective interfering (DI) particles: These defective mutants can only replicate if a "helper" virus is present. They can also interfere with the growth of normal viruses.

Viruses Interaction

Interaction of two or more viruses in the same host cell can occur via several mechanisms:
- Recombination: Exchange of genes between two viruses with high sequence homology. This is more common in double-stranded DNA viruses.
- Reassortment: Occurs in RNA viruses with segmented genomes (like influenza) and leads to genetic variation.
- Complementation: A nonfunctional viral protein from one virus can be complemented by a functional protein from another virus. This can be essential for defective viruses.
- Phenotypic mixing: Two viruses infecting a cell can result in progeny with mixed capsid proteins, potentially altering their tropism.
- Phenotypic masking (transcapsidation): The capsid protein of one virus surrounds the genome of another, producing progeny with altered tropism compared to the parental viruses.

Interference

Interference occurs when one virus inhibits the growth of another, often mediated by interferons. The inhibition can be due to factors such as competition for receptors or the production of inhibitors like interferons. Sometimes simultaneous infections can enhance viral yield (rather than hinder it).

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Description

This quiz covers the essential aspects of viral genetics, focusing on mutations and their implications for replication and vaccine development. It explores how different viruses interact within the host and the significance of mutation rates in RNA and DNA viruses. Test your knowledge on the mechanisms and consequences of viral mutations.