Viruses

Question 1

What is the importance of viruses?

Answer 1

For biological control, and cancer treatment – viruses can be harnessed for human benefit.

Question 2

Give an example of when a virus has crossed species boundary

Answer 2

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

Question 3

Who was the 1st to discover the virus?

Answer 3

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

Question 4

Define virus

Answer 4

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

Question 5

How can we study animal viruses?

Answer 5

By using embryonated eggs, cell cultures or living animals

Question 6

How can we study bacterial viruses?

Answer 6

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.

Question 7

If we cannot use antibiotics to fight viral disease, what do we use?

Answer 7

Vaccines

Question 8

How can we prevent infection?

Answer 8

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

Question 9

Does it use the hosts raw materials and synthesising machinery or its own?

Answer 9

The hosts.

Question 10

What is the ‘replication cycle’ of viral particles?

Answer 10

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

Question 11

Which proteins are required for viral replication?

Answer 11

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.

Question 12

How many classes does the Baltimore Classification have?

Answer 12

Seven

Question 13

What is the Baltimore Classification?

Answer 13

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.

Question 14

What is positive sense RNA?

Answer 14

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.

Question 15

With regard to positive sense RNA, in which direction does ribosome translation occur?

Answer 15

5’ to 3’

Question 16

What is negative sense RNA?

Answer 16

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

Question 17

What two things must a host cell be in order to allow viral synthesis?

Answer 17

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

Question 18

Why is DNA not able to replicate in neurons?

Answer 18

They do not divide, and therefore do not have active synthesis machinery and thus the virus will not survive

Question 19

What is the role of glycoconjugates in terms of cell targeting?

Answer 19

Glycoconjugates are displayed on the cell surface and act as receptors

Question 20

Outline the infectious cycle

Answer 20

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

Question 21

What are the two methods that viruses use to enter cells?

Answer 21

Internalisation via endocytosis

Internalisation via cell surface fusion

Question 22

What is cell surface fusion?

Answer 22

A highly regulated process which ensures that it is only the immune cells the become infected

Question 23

Which virus is known for using cell surface fusion as a method of entry?

Answer 23

HIV

Question 24

Why is knowing the methods by which viruses enter cells useful to us?

Answer 24

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

Question 25

What is the role of a viral capsid?

Answer 25

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