Viro - Lecture 5

drraythe's version from 2015-08-30 15:36

Viral Evolution

Question Answer
What is a genotype?Genetic constitution (may or may not vary from its phenotype, aka physical appearance)
What is a phenotype?Biological properties result of the expression from the genotype but modified by environmental factors
What is a reading frame?The initial nucleotide from which translation starts. Everything is read in three reading frames, each set of three codes for one amino acid. The actual frame in which the protein is supposed to be read is defined but a start codon ( knows where to start)
What is degeneracy?The redundancy of the genetic code. (Those degenerates, always copying me)
What are the three main ways viruses evolve?Mutations, recombination, & reassortment
What are some of the selection pressures viruses encounter?The stability of the outside environment (temp, pH, salt, etc), & the host's immune system
What is genetic "drift”?Slow evolution over time
What method(s) of evolution is/are considered genetic "drift"?MUTATIONS (small mutations over time change things). (Mutations can be substitutions, insertions, & deletions)
What are the three types of mutations?Substitutions, insertions, & deletions
What is genetic "shift"?A rapid & large genetic change.
What method(s) of evolution is/are considered genetic "shift”Recombination, reassortment, defective interfering particles
What is a point mutation?A mutation that only affects one or a very small amount of nucleotides (she said: exchange a single nucleotide for another)
Explain a silent mutationMutations which code for the same (or a sufficiently similar) amino acid. Will not change protein function
Explain a missense mutationMutations which code for a different amino acid (& will change the protein’s function)
Explain a nonsense mutationMutations which code for a stop & can truncate the protein
Explain "insertions"Add one or more extra nucleotides into the DNA. Can (but not always will) bc a shift in the reading frame
Explain "deletions"Remove one or more nucleotides from the DNA. Like insertions, these mutations can (but not always will) alter the reading frame of the gene
What is "indels"Cute little word for insertions or deletions
What is a frameshift mutation?Mutations that disrupt the reading frame sequence by indels (insertions or deletions) of a non-multiple of 3 nucleotide bases are known as frameshift mutations. These mutations usually result in translation of a completely different protein from the original & are also very likely to cause a stop codon to be read, which truncates the protein. These mutations may impair the function of the resulting protein
Which type of virus has a higher rate of mutations, & why?RNA viruses mutate more, bc they need to use RNA polymerase to replicate, & this enzyme doesn't have proofreading ability like the cells enzymes do
Cumulative point mutations, in combination w/ small insertions & deletions, are known as what?Genetic drift
Explain "quasispecies"Every population w/in a host is composed of varied genome alternatives (quasispecies) whereby one clone is predominant under the existing conditions bc it is better fit (why theyre better at not going extinct than us, basically)
Explain recombinationDuring recombination the RdRp (RNA polymerase) might jump from one template to another by a copy choice mechanism (the ability of the RdRp to detach & attach to a new template). This is a type of genomic shift!
Explain reassortmentReassortment, which occurs in segmented genome viruses, is another way of evolution constantly causing new strains. For example influenza, where animal & human strains reassort in a common host (probably pigs) & cause new variants to which the human population is naïve. This is a type of genomic shift.
How do defective interfering particles work?The DI particles carry mutant genomes. These defective genomes need the help of normal viral genomes to replicate. These genomes can act as highly flexible evolution modules that can tolerate large deletions or sequence rearrangements which may in the future be inserted back into a complete genome by recombination resulting in a major SHIFT in the phenotype (so, defective particles must be w/ regular particles too)
Viral products may interact, which may affect the viral proteins. These diff proteins may affect the ____, but if they dont affect the ___, they arent passed down to progenyPhenotype, genotype (so, phenotype might be changed w/out affecting the genotype)
Explain the importance of viral evolution in terms of the flexibility/adaptabilityViruses are extremely flexible (progeny numbers, replication time) which allow them to adapt to new hosts (jump species), reinfect the same host, evade the hosts immune response causing persistent infection etc
Explain the mechanism/the reason why attenuated vaccinations work (in terms of viral evolution)Passage in a new host imposes tremendous pressure & only the clones able to adapt will remain even if this means losing virulence in the former host. This is how many attenuated vaccines are obtained
If a virus evolves to be suitable for a different type of host than the original, they cant infect the old host, UNLESS...Back mutations or complementary mutations can bring virulence back
What is complementation?Can occur between strains from the same virus, between related viruses or two unrelated viruses. Cells infected w/ 2 different types of virus may rescue or increase the yield of one or both
What is phenotypic mixing?Progeny may acquire phenotypic characteristics from both parents (but contains the genome of only one). In naked viruses transcapsidation can occur
What is polyploidy?Except for retroviruses, viruses are haploid. But sometimes several nucleocapsids may be found in a single envelope