Outcome 1 - Viruses Flashcards
How do viruses acheive genetic variation
Through mutation and genetic recombination
What types of mutations do viruses undergo
Substituion, insertion and deletion
Name 3 ways through which viral mutations may arise
- Exposure to mutagens e.g UV light, chemicals
- Changes in chemical structure of bases
- Fallibility of replicating enzymes
Why are viral mutations important
Mutations may lead to changes in a virus with altered virulence or give rise to new viral serotypes
Why are DNA virus mutation rates lower than RNA virus mutation rates
DNA viruses utilise DNA polymerase which have proofreading cababilities whilst RNA viruses dont
What are the 3 possible fates of mutations
- Inactivation of essential protein
- Improved enzymatic activity
- Altered antigenicity of surface antigen (temporary advantage)
What is antigenic drift
Slow gradual accumulation of genetic mutations over time leading to phenotypic changes
What is antigenic shift
Rapid change in the genetic material of the virus
What is the impact of viral mutations on vaccines
Many vaccines are produced by growing viruses
under conditions that differ from the natural host.
This selects for mutations that do not allow the virus
to survive as effectively in the host any more.
When does viral recombination occur
When two viruses of different parent strains co-infect the same host cell and interact during replication, generating viral progeny that have genes from both parents.
What are the two mechanisms of recombination for viruses
Independent assortment and incomplete linkage
Describe viral recombination through independent assortment
When two viruses with segmented genomes trade segments during replication. The genes are unlinked and assorted at random. This can lead to antigenic shift.
Describe viral recombination through incomplete linkage
In DNA viruses when a break-rejoin mechanism causes linked genes to be fragmented from one another and then recombine. In some retroviruses recombination occurs after reverse transcription when the gene are in DNA form. Recombination can occur between two retroviruses or a retrovirus and host cell DNA
What is the result of incomplete linkage between a retrovirus and host cell DNA
It gives rise to a novel virus with some non-virus genes. If these host genes code for growth factors, growth factor receptors, or a number of other specific cellular proteins, the recombinant retroviruses may be oncogenic
How is viral recombination exploited for vaccine and gene therapy
Vaccinia virus strains could be produced that carry DNA coding for viral antigens. The presence of the antigen in the host will stimulate specific antibody production by the host.
