Microbiology 4- Viral properties

Question 1

What is the definition of a virus

Answer 1

Viruses are infectious OBLIGATE intracellular PARASITES

Question 2

Two key features of a virus

Answer 2

Structual simplicty

Intracelluar parasitism

Question 3

What are the 7 classes of virus?

Answer 3

dsDNA genome
ssDNA genome
dsRNA genome
\+sense RNA genome 
-sense RNA genome
ssRNA genome using dsDNA intermediate
ss/dsDNA genome using ssRNA intermediate

Question 4

4 Consequences of viral genome type

Answer 4

RNA viruses and retroviruses use their own polymerase to replicate.
These lack proof reading capacity leading to high mutation rate.

RNA viral genomes are limited in size due to inherent instability to RNA vs DNA. The largest RNA viruses are coronaviruses genome size around 30kb.
RNA viruses often use complex coding strategies to make more proteins than expected from a small RNA genome.

DNA viruses have genomes up to 100s kb.
There is plenty of room for accessory genes that can modify the host immune response.
These genes are often lost in passage in culture.

Segmented genomes allow an additional easy form of recombination known as reassortment, but also impose more difficult packaging strategies.

Question 5

6 steps in the generic virus replication cycle

Answer 5

1. ATTACHMENT- protien coat interacts with host cell receptors to gain acces to the cell
2. ENTRY- of the virus genome to the host cell and synthesis of viral mRNA
3. TRANSLATION- of viral mRNA into proteins
4. REPLICATION- of the the viral genome by asymmetric replication
5. ASSEMBLY- of the virus protiens into new virions, association and encapsidation of new genome
6. EXIT from the infected cells and dissemination to new hosts

Question 6

Replication cycle of HIV-1

Answer 6

1. Virus is on the outside
2. GP120 glycoprotein on virus capsule interacts with CD4 on the host cell membrane
3. Once it interacts with CD4 it can interact with a co-receptor (CCR5 or CXCR4) which brings the virus within close proximity of the cell membrane
4. Virus membrane and host membrane will fuse and viral content will be inserted into the cell
5. Enzymatic copying of viral genome by reverse transcriptase to produce viral DNA
6. The DNA moves into the nucleus and is integrated into the host genome
7. It is transcribed into mRNA and, subsequently, translated into proteins
8. All of these then come together at the cell membrane and produce a new virus particle which leaves the cell

Question 7

If you put a virus on healthy cells what happens?

Answer 7

you get a change in cell shape and you get cell death

This is the CYTOPATHIC EFFECT (CPE) which is defined as the death of the cell as a result of being infected by a virus

Question 8

What happens to a cell monolayer after the virus has killed the cell

Answer 8

viruses form plaques on cell monolayers

Question 9

Describe the process of Plaque assay

Answer 9

Take a sample from the patient that contains the virus

Make serial 10 fold dilutions

Take a known volume of the dilutions and put it onto the susceptible cells

There will be plaques on the susceptible cells showing how many viruses there are in the dilution

Question 10

What is syncyita

Answer 10

Viruses with surface proteins that can fuse at neutral pH often fuse cells together

Can be used to tell if a sample contains a virus

Question 11

What is Immunostaining virus infected cells

Answer 11

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 12

5 viral diagnosis

Answer 12

Detecting Viral Genome
PCR
Have primers which are complementary to a specific part of the viral genome which identifies the virus
Use sets of primers and the one which shows up positive will identify the virus

Detecting Viral Antigen
Indirect Fluorescence Antibody (IFA)
ELISA

Detecting Viral Particles
Electron Microscopy
Haemagglutination Assay

Detecting virus cytopathic effect in cultured cells
Virus isolation

Detecting antibodies to virus
Serology