Viral properties

Question 1

What technique is used to prove that a virus is causing a particular disease?

Answer 1

Koch’s Postulates

Question 2

List Koch’s postulates: Microorganism…

Answer 2

Found largely in all diseased animals, but not healthy ones.
Must be isolated from a diseased animal and grown outside body in a pure culture.
When injected into other healthy animals, produces same disease.
When recovered from experimental hosts, isolated, compared to 1st microorganism, found to be identical.

Question 3

Virus definition

Answer 3

infectious OBLIGATE intracellular PARASITES

Question 4

Virus genetic makeup

Answer 4

Genome comprises DNA or RNA
Single or double stranded DNA
Positive or negative sense or double stranded RNA

Question 5

What does a virus do once inside an appropriate cell?

Answer 5

Viral genome is replicated and directs synthesis, by cellular systems, of more viral components and genomes.

Question 6

Size of a virus

Answer 6

100nm
Small: only visible with electron microscope
(smaller than most bacteria)

Question 7

What are the 2 broad types of virus morphology?

Answer 7

Non- enveloped: outer layer of capsule is a protein shell.

Enveloped: Lipid envelope derived from host membrane

Question 8

What virus has a combination of a capsid and envelope

Answer 8

Herpes

Question 9

Baltimore classification system

Answer 9

Grouping of viruses based on genomes & how they choose to replicate them

Question 10

Give 3 examples of non-enveloped viruses

Answer 10

Adenovirus
Picornavirus
Calicivirus

Question 11

Give 2 examples of enveloped viruses

Answer 11

Pleiomorphic: Measles virus

Typical shape: Ebola virus

Question 12

What are the different groups in the Baltimore classification?

Answer 12

DNA Viruses (double and single stranded)
RNA Viruses (positive sense, negative sense, double stranded)
DNA and RNA Viruses (retroviruses, double stranded DNA (RT))

Question 13

What is the difference between positive sense RNA and negative sense RNA?

Answer 13

Positive sense RNA can be translated straight away

Negative sense RNA must be transcribed into a positive sense copy

Question 14

What are some common features among RNA viruses and retroviruses?

Answer 14

Use their own polymerase to replicate

These lack proof reading capacity= high mutation rate

Question 15

Why are RNA viral genomes limited in size?

Answer 15

Inherent instability

Largest= 30kb

Question 16

What are some common features among DNA viruses?

Answer 16

Larger because DNA is more stable
Up to 100kb
Plenty of space for accessory genes that can modify host immune response

Question 17

What is a positive of having a segmented genome?

Answer 17

Allows reassortment: an additional easy form of recombination

Question 18

What is a negative of having a segmented genome?

Answer 18

More difficult assembly of components before virus can leave cell

Question 19

Virus replication cycle

Answer 19

Proteins on coat/ envelope of virus bind to receptors on surface of host cell
Once inside, ‘uncoats’, so its genome can gain access to host cell machinery
Uses cell ribosomes to make proteins (early= regulatory- turn cell into ‘factory’, late= structural)
Replicates its own genome with own/hosts polymerase
Newly synthesised genomes and viral proteins assemble
Burst out of cell to infect more

Question 20

What is a target point in the replication cycle of HIV-1?

Answer 20

Process of reverse transcription (making DNA from RNA) unique to retroviruses

Question 21

Each virus has unique/ further steps in their replication cycle

Answer 21

These can be targeted in therapy

Question 22

What is the cytopathic effect?

Answer 22

Death of a cell as a result of being infected by a virus

Question 23

How can viral plaques be used to quantify the amount of virus in a sample through completing a plaque assay?

Answer 23

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

Question 24

What are 2 other ways of detecting the presence of virus in a sample?

Answer 24

Syncytia formation

Immunostaining

Question 25

What is syncytial formation?

Answer 25

Viruses with surface proteins that can fuse at neutral pH often fuse cells together e.g. HIV
Count No of syncytium to calculate No viruses present

Question 26

What is immunostaining?

Answer 26

Antibodies generated in the lab to unique virus proteins indicate which cells are infected or where in the cell the virus proteins are located.

Question 27

What are the 3 phases of growth of a virus?

Answer 27

Eclipse: enters cell, appears to disappear
Logarithmic: replicates exponentially
Cell Death

Question 28

What are the 5 techniques used to diagnose a viral infection?

Answer 28

Genome: PCR
Antigen: Indirect Fluorescence Antibody, ELISA
Viral Particles: Electron Microscopy, Haemagglutination Assay
Cytopathic Effect in cultured cells (virus isolation)
Antibodies to the virus (serology) (take infected blood)

Question 29

Propogating viruses:

Can grow viruses in lab by providing permissive cells, often continuous lines of transformed cell cultures.

Answer 29

Viruses may accumulate mutations that adapt them to ‘new’ host.
Can lead to attenuation: was the basis for generation of vaccines in the past.

Question 30

Name 2 viruses that we have no permissive cell lines for

Answer 30

Norovirus

Hepatitis C

Question 31

Reverse genetics can be used to

Answer 31

create viruses with engineered mutations in their genomes