Flashcards in L36_Viral Genetics Deck (20):
Order the following viruses from largest to smallest genome: Parvovirus, Adenovirus, Papillomavirus, Retrovirus, pox virus, herpes virus
Parvovirus (2), Retro virus (3), Papillomavirus (8), Adenovirus (10), Herpes Virus (70), Pox Virus (up to 200)
Are virus genes prokaryotic or eukaryotic?
how does the virus genome determine the cell tropism of the virus?
Each virus promoter binds specific transcription factors. If these factors are not present in a cell the virus will not survive. e.g. papillomavirus gene expression is regulated by keratinocyte factors, thus it is skin specific.
Describe some strategies viruses use to have an extremely efficient genome.
No wasted space
overlapping reading frames
translational frame shifts
Are viral polyproteins cleaved by viral proteases or host proteases? Why is this important?
Viral, which makes them a good target for drugs
What genomes are more stable RNA or DNA viruses?
What is a possible advantage of high viral mutation rates.
It helped us to create live attenuated viruses that would maintain antigens to cause immunity but would be less virulent in humans
What are the four possible viral interactions that can happen if two viruses infect the same cell?
describe viral complementation
When two defective viruses complement each others deficiencies and together are viable...the progeny however are the same as the two original viruses
Describe phenotypic mixing of similar viruses
Two viruses that infect the same cell may acquire protein coats from the other virus. While each virus maintains its original genome, its phenotype may be altered such that it can infect a new cell type. This only lasts for one generation. (The altered phenotype viruses are called pseudotypes)
Describe recombination of 2 viruses.
2 viruses that infect the same cell that happen to have extended homologous sequences can cross over. This results in a permanently altered chimeric genome.
Describe reassortment of viral genomes?
If two segmented viruses enter the same cell, segments from each may be mixed when the other when encapsulation occurs resulting in a new combination of segments. (creates new strains of flu that cause the outbreaks)
How can viruses cause genomes in host cells to mutate?
By insertion into the host genome
Why is infection by 2 viruses rare?
Blocking of receptors
Competition for Resources
stimulation of innate immunity (interferons)
all of this caused by first virus usually prevents second virus from entering
How many genes can feasibly be delivered by viral gene therapy?
only 1-2, any more gets too complicated at this point.
What are the steps in developing a viral gene therapy?
1 Deletion of essential gene in virus and insertions of that essential gene into a packaging cell
2 Clone the therapeutic gene to virus
3 grow the virus in the packaging cell (Via complementation)
4 Test in cells - animals - humans
What are some disease that lack a single gene that may be treated with viral gene therapy?
various enzyme deficiency disorders
What two types/classes of diseases are particular targets for viral gene therapy?
Single gene disorders and cancer therapy
What are some of the obstacles that have been encountered in viral therapy?
1 non-replicating Virus is not spreading in tumors (possibly add promoters that make them only grow in target cells)
2 only transient expression of foreign gene
3 low efficiency of gene transfer (need a ton of virus)
4 Inflammation in response to the virus
5 potential for chromosomal disturbances by virus