Introduction to Virology

Question 1

Properties of viruses

Answer 1

Obligate intracellular
can’t grow or replicate outside host
don’t acquire nutrients, produce energy or synthesise proteins
Host specific
Amongst smallest biological entities (30-400 nm)
Genome size varies from 3.2 kb (4 genes) to 1.2 Mb (911 genes)

Question 2

Viral classification

Answer 2

Viruses don’t fit in tree of life
Can be classified on:
type of nucleic acid
morphology
presence/absence envelope
host organism

Question 3

DNA viruses

Answer 3

ssDNA-Parvovirus
dsDNA-Smallpox, Herpes

Question 4

RNA viruses

Answer 4

ssRNA-Polio,Rhinovirus,Ebola,SARS-Cov2,Influenza
dsRNA-Rotavirus

Question 5

RNA<–>DNA viruses

Answer 5

ssRNA- retrovirus- HIV

dsDNA-hepadnaviruses- Hepatitis B

Question 6

Structure of viruses

Answer 6

Naked viruses
no outer membrane e.g. polio virus
Enveloped viruses
outer membrane e.g. herpes simplex virus, SARS-Cov2
derived from host cell membrane
modified with viral proteins for recognition and attachment to host cells

Question 7

Viral multiplication

Answer 7

1. Attachment’
2. Entry and uncoating
   Entry of naked virus by endocytosis
   Fusion of enveloped virus
3. Synthesis of viral components
4. Assembly
5. Release

Question 8

1. Attachment

Answer 8

Viruses are not motile; initial contact from random collision
This is followed by specific interaction between attachment site on viral surface and receptor on cell surface
e.g. HIV - CD4 protein on T-helper cells
e.g. SARS-Cov2 – ACE2 receptor on epithelial cells

Question 9

2. Entry and uncoating

Answer 9

Entry and uncoating often coupled process
Entry through endocytosis (enveloped and naked virus)
Entry through fusion with membrane (enveloped virus)
During or shortly after entry nucleic acid is prepared for expression/replication: full or partial shedding of capsid proteins (uncoating)
Fusion of enveloped virus

Question 10

3. Synthesis of viral components

Answer 10

Viral nucleic acid competes with host cell for control of biological machinery
Viral mRNA is produced
mRNA directs synthesis of early proteins
early proteins direct nucleic acid replication
Synthesis of late proteins

Question 11

4. Assembly

Answer 11

Nucleic acid is either
packed into preassembled capsid
or
associates with capsid proteins during formation

Question 12

5. Release

Answer 12

Cytolysis
mostly for naked viruses
Budding
enveloped viruses
envelope usually derived from plasma membrane

Question 13

Outcomes of viral infection

Answer 13

Cytocidal infection e.g. polio virus
Chronic infections e.g. hepatitis B virus
Latent infection e.g. HIV, Herpes simplex virus
Transforming infections e.g. human papilloma virus (HPV) or human T-cell leukaemia virus-1 (HTLV-1)

Question 14

Production of viral vaccines

Answer 14

live vaccine
killed vaccines
componet vaccines
vector vaccines
mRNA vaccines
DNA vaccines

Question 15

live vaccines

Answer 15

using attenuated strains

Question 16

killed vaccines

Answer 16

viruses killed by heat or chemicals

Question 17

component vaccines

Answer 17

isolated from whole virus particles
produced by recombinant DNA technology

Question 18

vector vaccines

Answer 18

viral vector carrying component from pathogen

Question 19

mRNA vaccines

Answer 19

mRNA encoding antigen introduced into tissue

Question 19

DNA vaccines

Answer 19

introduction of plasmid encoding antigen into tissue

Question 20

Cell cultures

Answer 20

infect mammalian cell line with virus
isolate and purify virus particles

Question 21

Embryonated hen’s eggs

Answer 21

virus injected into fertilised chicken eggs
eggs incubated 2-3 days
isolate and purify virus particles