Infection & Immunity: General Concepts (Incomplete)

Question 1

How big are viruses?

Answer 1

20-300nm, cannot be visualised with light microscope

Question 2

How do viruses replicate?

Answer 2

Dependent on host cell as viruses cannot produce their own energy or proteins. Once a virion infects a cell, can replicate within hours –> 100s virions –> rapid spread from cell to cell.

Question 3

What is the structure of a virus?

Answer 3

Core nucleic acid surrounded by protective protein (capsid).

Sometimes capsid is covered by lipoprotein envelope (which creates instability).

Question 4

What is the role of capsid?

Answer 4

Mediates attachment of virus to specific host cell receptors

Defines the species specificity and organ specificity

May induce host immune responses

Question 5

What effect does the lipoprotein envelope have on viruses?

Answer 5

Confers instability

If enveloped (e.g. RSV), rapidly dries out in external environment and readily inactivated by detergent/alcohol.

If no envelope (e.g. rotavirus, Norwalk virus) - less easily eradicated in external environment

Question 6

How are viruses classified?

Answer 6

Nucleic acid (DNA vs RNA)
Capsid size and symmetry
Envelope

Question 7

How do viruses cause cell death?

Answer 7

Inhibition of host cell protein synthesis (but allowing viral protein synthesis). Can be seen in cell cultures under light microscope (cytopathic effect or CPE) - this can help with diagnosis.