Viral Properties Flashcards
What technique is used to prove that a virus causing a particular disease?
Koch’s Postulates
Define virus.
Infectious obligate intracellular parasites
What is the average size of a virus?
100nm
What are the two broad types of virus morphology?
Non-enveloped – protein capsid
Enveloped – membrane derived from host membrane
What is the main classification of viruses and what is it based on?
Baltimore Classification – based on the genome
What are the different groups under this classification?
DNA Viruses (double stranded, single stranded) RNA Viruses (positive sense, negative sense, double stranded) DNA and RNA Viruses (retroviruses, double stranded DNA (RT))
What is the difference between positive sense RNA and negative sense RNA?
Positive sense RNA can be translated straight away
Negative sense RNA must be transcribed into a positive sense copy
What are some common features among RNA viruses and retroviruses?
Small genome limited by instability of RNA
No proofreading capacity – high mutation rate
What are some common features among DNA viruses?
Larger because DNA is more stable so there is space for accessory genes
What are the good and bad aspects of having a segmented genome?
Good – allows an opportunity for exchanges of genetic material and fast evolution
Bad – all the segments need to be assembled when the virus leaves the cell
Describe the replication cycle of HIV-1.
GP120 receptors on the HIV bind to CD4 receptors on T cells and bind to co-receptors (CCR5 or CXCR4) allowing the membranes to fuse and the viral contents to enter the cell
Some copies of the virus genome gets replicated
Some gets reverse transcribed to viral DNA, which is integrated into the host genome.
It is then transcribed and translated into proteins
The proteins and copies of the genome then assemble to form new virus particles, which exit the cell.
What is the cytopathic effect?
Death of a cell as a result of being infected by a virus
How can viral plaques be used to quantify the amount of virus in a sample?
Plaque Assay – the virus undergoes serial 10-fold dilutions and is then spread on a monolayer of susceptible cells
A plaque will appear where an individual virus has killed some cells
The number of plaques can be counted and scaled up to quantify the amount of virus in a sample
What are two other ways of detecting the presence of virus in a sample?
Syncytia formation
Immunostaining
What are the three phases of growth of a virus?
Eclipse
Logarithmic
Cell Death
