8 - Intro to Virology

Question 1

Viruses

Answer 1

• Inert outside of living host
• Cause infection and disease
• Most known viruses do not cause disease in humans

Question 2

Which four traits define viruses

Answer 2

• Viruses are obligate intracellular parasites that have an infectious extracellular stage (virion)
• All viruses encode at least one capsomere protein (cover and protect the genetic material)
• All viruses replicate by assembly (cells infected by viruses synthesise the components of the virion)
• Viruses have the capacity to evolve through typical evolutionary processes that
  alter nucleic acids in a heritable way

Question 3

Obligate intracellular parasites

Answer 3

Require host cells to multiply. Don’t contain the machinery for protein synthesis and energy production

Question 3

Capsid

Answer 3

The protein coat of capsomeres that surround the nucleic acids

Question 4

two classes based on external layer

Answer 4

Enveloped virions (have a lipid bilayer) and naked virions which don’t

Question 5

Shapes of capsids

Answer 5

Icosahedrons (spherical) or helical

Question 6

nucleocapsid

Answer 6

the nucleic acid genome and the capsomeres are so intimately associated (e.g. SARS-CoV2)

Question 7

Viral genomes

Answer 7

• DNA or RNA
• Single or double stranded
• Linear or circular

Question 8

Baltimore classification

Answer 8

Classification of viruses according to the ways they synthesise and use mRNA

Question 9

Central dogma

Answer 9

DNA –> RNA –> Protein

Question 10

Why is light microscopy important in virology if most viruses are too small to be seen by a light microscope

Answer 10

Because it can be used to visualise the effects of virus infection on host cells

Question 11

quasispecies

Answer 11

The individual variant viruses within a species

Question 12

Size of viruses

Answer 12

Less than 200nm (10^-9m) in diameter/length

Question 13

Mimiviruses size

Answer 13

500nm in diameter

Question 14

Virus induced cytopathic effects (CPE)

Answer 14

• Syncytia: Large, multinucleate cells
• Inclusion bodies: visible when host cell is stained, sites of viral gene expression, genome replication, assembly
• Transformed cancerous cells grow on top of each other, not responding to contact inhibition

Question 15

What can virus names be based on

Answer 15

• The diseases they cause
• Symptoms they cause
• The parts body they infect
• The geographical location where they first emerged
• The properties of their virions

Question 16

Culturing viruses

Answer 16

• Cultured in animal and human cells. Continuous cell lines used
• Can also be cultured in eggs

Question 17

What does prion stand for

Answer 17

Proteinaceous infectious particle

Question 18

Prions

Answer 18

• Normal prion protein PrP (PrP^c) encoded by PRNP gene is present in neurons
• More than 30 abnormal forms (PrP^Sc) identified in
  people with familial disease
• Cause spongiform encephalopathies (large vacuoles in brain)
• The abnormal PrP^Sc can attach to PrP^c and promote its transformation into PrP^Sc
• Abnormal protein builds up in brain, forming clumps that destroy neurons

Question 19

Features of spongiform encephalopathies

Answer 19

• Changes in memory, personality an behaviour
• Dementia
• Abnormal movements (ataxia)

Question 20

Animal prion diseases

Answer 20

• Scrapie in sheep
• Chronic wasting disease in deer
• Mad cow disease (Bovine spongiform encephalopathy)

Question 21

Human prion diseases

Answer 21

• Fatal familial insomnia
• GSS
• creutzfeldt-jakob disease (human form of BSE)