V1

Question 1

Define virus

Answer 1

An infective agent that typically consists of a nucleic acid molecule in protein coat and have absolute requirement for living host to replicate

Question 2

List properties of a virus

Answer 2

• Genome: DNA or RNA, never both
• Capsid: protein coat
• Envelope or membrane

Question 3

What is the size of viruses?

Answer 3

Viruses are smaller than limit of resolution of the LM, so EM must be used to see viruses.

Question 4

What are the characteristics of a viral genome?

Answer 4

• Hereditary information
• First generation undergoes replication to form new generation
• can be single/double stranded
• can be linear/circular
• can be continuous/segmented

Question 5

How are viruses classified?

Answer 5

• Currently classified according to genome, replication strategy, capsid symmetry, and phylogenetics.
• Grouped into order, family, subfamilies and genera

Question 6

How are viruses classified according to their genome?

Answer 6

• DNA viruses
• RNA viruses
• double stranded or single stranded?

Question 7

Define viroid

Answer 7

A virus-like agent with RNA replicating agents and no encoded proteins, they only infect plants

Question 8

Define prion

Answer 8

Proteinaceous infective agent with no nucleic acid. They behave infectiously and cause a change in protein folding.

Question 9

Which diseases are caused by prions?

Answer 9

Kuru, Fatal Insomnia, Creutzfelt Jakob,

Gerstmann-Straussler-Schneiker

Question 10

Define defective viruses

Answer 10

Viruses that cannot replicate on its own and need a helper virus to infect cells

Question 11

List the different ways in which viruses can be inactivated or sterilised

Answer 11

• autoclaving (121 degrees Celsius for 15 minutes)
• formalin
• ethylene oxide
• surface decontamination: glutaraldehyde, formaldehyde, hypochloride.