Viruses Flashcards
What is the importance of viruses?
For biological control, and cancer treatment – viruses can be harnessed for human benefit.
Give an example of when a virus has crossed species boundary
An example could be mosquitoes infect humans such as with dengue fever, Zika virus and yellow fever. Middle east respiratory syndrome is an example of when camels infect in humans
Who was the 1st to discover the virus?
Ivanosky found that tobacco mosaic disease is smaller than bacteria, this discovery was followed by the Beijerick who found that viruses could not be propagated into liquid media, again this was followed by Loeffler and Frosch who found the cause of foot and mouth disease and finally Stanley who discovered TMV was crystallised
Define virus
A small, obligate intracellular parasite that requires a host to live, it’s simple structure and small genome only codes for the essentials- it has circular DNA or RNA, and no metabolism as it uses the hosts synthesising machinery to replicate
How can we study animal viruses?
By using embryonated eggs, cell cultures or living animals
How can we study bacterial viruses?
By using the plaque method, this is where you mix a sample with phages and pour it onto a plate. The viral infection forms plaques- which are made up of lysed cells. The plaques are counted.
If we cannot use antibiotics to fight viral disease, what do we use?
Vaccines
How can we prevent infection?
Using anti-viral drugs, change the stigma around prevention (such as with the use of condoms), slaughter infected animals, restrict animal movement and control vectors
Does it use the hosts raw materials and synthesising machinery or its own?
The hosts.
What is the ‘replication cycle’ of viral particles?
The virus enters the cell, the viral DNA is converted to mRNA and transcribed, the mRNA become capsid proteins and combine with viral DNA (that has been replicated), to self assemble into new viral particles- which then exit the cell
Which proteins are required for viral replication?
Non-structural proteins are the tools, they are the enzymes that replicate the viral genome. They are required inside the cell, in small amounts, immediately upon infection- they DO NOT become part of the virus
Structural proteins are the bricks, they are needed to form the progeny particles and are required in large amounts. They are only useful once the genome is replicated.
How many classes does the Baltimore Classification have?
Seven
What is the Baltimore Classification?
It looks at the unique pathways that viruses use to produce their mRNA as this can be used to define a virus into one of the 7 classes.
What is positive sense RNA?
A very short mRNA molecule, that requires 4 things to function- a methylated cap, start/ stop codon, Poly-A tail, and an open reading frame.
With regard to positive sense RNA, in which direction does ribosome translation occur?
5’ to 3’
What is negative sense RNA?
A compliment (not a copy) of mRNA sense, it is related to positive sense RNA due to complimentary base pairing. It cannot be translated and therefore does not make proteins. It may be transcribed, creating a strand of positive sense RNA- which can be translated and produce proteins
What two things must a host cell be in order to allow viral synthesis?
Susceptible- it must have the right cell attachment factors, receptors and co-receptors
Permissive- it must have the right tools and bricks to support replication
Why is DNA not able to replicate in neurons?
They do not divide, and therefore do not have active synthesis machinery and thus the virus will not survive
What is the role of glycoconjugates in terms of cell targeting?
Glycoconjugates are displayed on the cell surface and act as receptors
Outline the infectious cycle
The virus enters the cell, the viral genome is translated creating viral proteins, the viral genome is replicated creating viral DNA, the viral proteins and viral DNA come together to create new virions, which then exit the cell
What are the two methods that viruses use to enter cells?
Internalisation via endocytosis
Internalisation via cell surface fusion
What is cell surface fusion?
A highly regulated process which ensures that it is only the immune cells the become infected
Which virus is known for using cell surface fusion as a method of entry?
HIV
Why is knowing the methods by which viruses enter cells useful to us?
As we can develop ways to block their entry pathway in order to minimise the chances of replication, and reduce the prevalence of a particular viral infection
What is the role of a viral capsid?
The capsid has three functions: 1) it protects the nucleic acid from digestion by enzymes, 2) contains special sites on its surface that allow the virion to attach to a host cell, and 3) provides proteins that enable the virion to penetrate the host cell membrane
