Viral Genetics Flashcards
What is viral genetics?
It’s the knowledge of mechanism of heritable information in virus.
This heritable information included: Genome structure, replication and genetic changes .
What is the reason why virus are continually changing?
Genetic selection
What are the two phenomenon in which virus change their genomic structure
Mutation and recombination
Phenotypic structure of virus can be changed by?
Interaction between viral grne products.
What is mutation?
It’s the change in the DNA sequence of an organism.
This is a result of error during replication.
Does mutated virus survive if mutation proved to be lethal?
No they don’t
In what condition does mutated virus survive?
I) if it provides selective advantage.
I’m) if it occurs early in the course of infxn
What is genetic recombination?
It is the rearrangement of DNA sequences by the breakage and rejoining of chromosomes or chromosome segments.
List the four types of genetic recombination:
Intramolecular recombination.
Reassortment
Reactivation
Market rescue/Cross activation.
What is reassortment?
This is the exchange of segments between virus to produce various stable virus.
Five an example of a virus type that reassortment occur in
Segmented virus
Give an example of viruses that undergo reassortment
Arenaviridae
Birnaviridae
Influenza virus A&B
Reoviridae
How many segments does Arenavirus have?
2
Birnaviridae has how many segments?
2
Reoviridae has how many segments?
10-12
Buynavirus has how many segments?
3
Influenza A and B virus has how many segments?
8
Explain the mechanism of Reactivation
. Two virions of the same strain that are lethally mutated in different genes coinfect a host
This results to viable recombinants
List the types of virus that undergoe reactivation;
Tips ROP
Poxvirus
Orthomyxovirus
Reovirus.
Explain the mechanism of reassortment
An infectious virus and an inactivated virus infects a host simultaneously.
The progeny of infectious virus is produced having active genes from both virus.(Infectious and inactivated)
Between what other type of virus can cross reactivation occur?
Infectious & a non infectious virus
Two infectious virus.
Two noninfectious virus.
List the three types of interactions between gene Viral products
Complementation
Phenotype mixing
Interference
What is complementation
This the interaction of viral gene products in cells infected by two viruses.
Here one or both virus may be defective.
Defective virus: lacks one or more fxnal genes.
If both virus are defective, the fxnal gene of one virus synthesis genetic product (Proteins and enzymes) for the other and vice versa, allowing the growth of both viruses.
If only one is defective, the other stable virus synthesis genetic product that complement the defective virus.
Can complementation occur between unrelated viruses?
Yes
What is phenotypic mixing
This happens in both enveloped and non enveloped virus.
It is an association of a genotype with a heterologous phenotype.
When two genetically diff virions of same family infect a cell: They can be :
I) Incorporation of the genome of one virus to the capsid protein of another virus -TRANSCAPSIDATION.
This is not a stable genetic change B/c upon replication the phenotypically mixed paren will yield progeny with capsids derived from its genome.
ii) In enveloped virus: PSEUDOTYPE FORMATION.
Virus doesn’t have to closely related.
Nucleocapsid of one virus becomes encased completely with an envelope of another OR
🌻It can be incompletely enveloping with the phenotypically mixed virus having a portion of its normal envelope with antigen and that of the other virus with their antigen.
Why is that phenotypic mixing usually occurs btw different members of same virus family?
This is so that the intermixed capsid Proteins must be able to interact with the capsid to form structurally intact capsid.
The phenomenon where two viruses simultaneously infect a cell and increases the yield of another is known as?
Enhancement.
The phenomenon where two viruses simultaneously infects a host and inhibit the growth of another is known as
Interference.
List the 3 mechanism at which interference can occur;
1)Virus A inhibts the ability of Virus B to get absorbed into the cell by blocking or destroying their common receptor.
2) Virus A competing with virus B for its replication components (Polymerase, translation initiation factor)
3) Virus A induces Virus B to produce an inhibitor called Interferon preventing the replication of Virus A
