POS - Virology Replicatio

Question 1

How do viruses attach to cell surfaces?

Answer 1

Proteins/glycoproteins on the virus cell surface bind to receptors.

Question 2

What is tropism?

Answer 2

Virus-receptor interaction determines specificity of viruses for cells and tissues

Question 3

How does a virus attach to the cell?

Answer 3

Via multiple receptors or co-receptors with spike cleaved by enzymes preparing it for entry.

Question 4

How does a virus enter the cell?

Answer 4

Via endocytosis, where the virus is released from an endosome by a pH change, and the viral envelope fuses with the endosomal membrane.

Via fusing directly

Question 5

What is uncoating?

Answer 5

The release of viral nucleic acid from a viral capsid.

• Some capsids only partially disintegrate
• Some are still in a nucleoprotein complex

Question 6

What is the classic viral replication cycle?

Answer 6

1. Viral entry
2. Replication
3. Transcription and translation
4. Assembly
5. Egress

Question 7

What are the 4 things viruses must be able to do?

Answer 7

Replicate the genome
Produce viral protein
Assemble new viral particles
Avoid the immune system

Question 8

How is mRNA synthesised from DNA viruses?

Answer 8

mRNA is transcribed in the nucleus using cellular RNA polymerase.

mRNA is transported to ribosomes for translation

Question 9

How is mRNA synthesised from RNA viruses?

Answer 9

Viruses need to use their own enzymes to make messenger RNA (RdRp)

RNA viruses remain in cytoplasm for replication and must avoid degradation

Question 10

What is the difference between late and early proteins that are translated?

Answer 10

Early proteins - non-structural proteins (regulate viral transcription and replication)
Late proteins - structural proteins (capsid and envelope glycoproteins)

Question 11

Where does genome replication occur?

Answer 11

DNA viruses - in nucleus
RNA virus - in cytoplasm

Question 12

What are the exceptions to where genome replication occurs?

Answer 12

Pox viruses - viral factories in the cytoplasm
Influenza - replicates in the nucleus

Question 13

How are genomes packaged into new particles?

Answer 13

Requires packaging signals to concentrate the viral components and is v complex

Question 14

What are the three ways a virus can be released?

Answer 14

1. Budding from plasma membrane
2. Exocytosis
3. Lysis of cell

Question 15

Why grow viruses in the lab?

Answer 15

Research
Vaccine production
Virus as a tool
Diagnostics

Question 16

What happens when you use chicken eggs to culture viruses?

Answer 16

Use 10 day old eggs - fertilised and requires sterile inoculaiton

Use different spaces depending on the virus: chorioallantoic, aminotic, yolk sac and allantoic

Question 17

What are the advantages/disadvantages to culturing cells in vitro?

Answer 17

Easy to handle and easy to scale up, easy to obtain as well

Question 18

How are cell cultures maintained?

Answer 18

Grow and cover the whole flask, treated with trypsin to detach from a plastic and then are passaged to a new flask.

Question 19

What are primary cell cultures?

Answer 19

From a tissue sample, can survive for 10-15 days before differentation occurs preventing further cell division

Question 20

What are continuous cell lines?

Answer 20

Immortalised cells that continue to grow and are derived from tumours.

Often lose receptors and have major abnormalities

Question 21

What are organoids?

Answer 21

3D cell cultures derived from stem cells and can be used to model donors/cell growth etc

Question 22

What are cytopathic effects?

Answer 22

Visible changes to cells following viral infections

e.g. the cells round up and detach or holes appear

Question 23

What are syncytia formation?

Answer 23

Cells fuse to create large cells with several nuclei

Question 24

What are inclusion bodies?

Answer 24

A mass of viral proteins within the cell

Question 25

What are non-cytopathogenic viruses?

Answer 25

Nor all cells produce a cytopathogenic effect, need staining or qPCR to detect.

Question 26

What are infectivity assays?

Answer 26

Used to quantify the number of infectious virus particles.

Question 27

What is plaque assays?

Answer 27

A type of infectivity assay. Its done by 10 fold serial dilutions of virus samples and the virions infect cells giving rise to plaques.

Counting plaques - calculate virus titre