Virology

Question 1

What are virions?

Answer 1

Virus particles

Question 2

What are viruses

Answer 2

Acellular organisms whose genomes consist of nucleic acid, and which obligately replicate inside host cells using host metabolic machinery and ribosomes to form a pool of components which self assemble into particles called virions, which serve to protect the genome and to transfer it to other cells

Question 3

What are prions?

Answer 3

Infections bits of protein folded in a way that can induce the folding of other proteins

Question 4

Process of T4 caliphate infecting E. coli

Answer 4

1. Tail fibres recognise host first
2. Tail fibres attach
3. If enough tail fibres attach (say all 6) then base plate can attach to specific receptors on host cell surface
4. Conformational change from base plate binding to surface of cell causes outer tail to contract
5. Base plate remains attached, so contraction of outer tail forces inner rigid part of tail (a tube) into the cell wall
6. Inner tail has enzymes at its terminus which dissolve their way through the cell wall
7. Molecular motor engages - drives DNA into cytoplasm

Question 5

What is viromics?

Answer 5

The study of viruses at genome and population level

Question 6

Size of virus genomes

Answer 6

Range from 1800 nucleotides (ssDNA) up to 2.5mil nucleotides (dsDNA in pandoraviruses)

Question 7

7 Baltimore Classes

Answer 7

1. dsDNA genomes: dsDNA viruses replicating semi-conservatively via a DNA intermediate
2. ssDNA genomes: ssDNA viruses replicating semi-conservatively via a dsDNA intermediate ending with dsDNA in particles
3. dsRNA genomes: dsRNA viruses replicating conservatively via ssRNA+ intermediate
4. ssRNA+ genomes: ssRNA viruses with (+)-sense genomes replicating semi-conservatively via ssRNA(-) intermediate
5. ssRNA- genomes: ssRNA viruses with (-)-sense genomes replicating semi-conservatively via ssRNA(+) intermediates
6. Retrovirus Genomes: diploid” ssRNA viruses which replicates via reverse transcription (RNA-dependent DNA polymerase used) with a greater-than-genome-length dsDNA intermediate
7. Pararetrovirus Genomes: dsDNA viruses which replicate via reverse transcription with a greater-than-genome-length ssRNA+ intermediate.

Question 8

Evolution of Eukaryotic RNA Viruses

Answer 8

• Small zoo of RNA viruses in prokaryotes before eukaryogenesis
• 2 lineages of prokaryotic viruses directly became eukaryotic RNA viruses:
  o Leviviridae gave rise to eukaryotic Narnaviridae
  o Cystoviridae
  gave rise to eukaryotic Reoviridae
• Rest of eukaryotic RNA viruses arose during Eukaryogenesis
• dsRNA viruses have polyphyletic origin (Not 1 original source)

Question 9

Evolution of Megaviruses

Answer 9

• Relationship to prokaryote viruses
• Big DNA viruses have massive complicated genomes (biggest are considerably bigger than smallest cells)
• Have genes coding for metabolic pathways as well as ribosome components
• Mimivirus:
  o First representative found
  o ±300 nm
  o Has ‘stargate’ that opens to release genome inside a cell because the genome is too big to spool out using molecular motor

Question 10

Origin of herpes-like dsDNA viruses

Answer 10

Directly from prokaryotic viruses

Question 11

Origin of adeno-like dsDNA viruses

Answer 11

Directly from prokaryotic viruses

Question 12

Human Adenovirus type 36

Answer 12

• Isometric, icosahedral, Has antennae on surface that attach to host cells
• Involved in development of obesity (more likely to become obese if had adenovirus)

Question 13

Human Herpesvirus

Answer 13

• ±250 000 base pairs; double-stranded DNA, lots of spikes

- Causes variety of diseases (not only herpes)

Question 14

HIV

Answer 14

• Envelope spikes

- 4 layers (outer membrane with envelope proteins; matrix shell; capsid; helical nuclear protein)

Question 15

Influenza virus

Answer 15

• Similar structure to HIV
• Envelope glycoproteins (2 kinds)
• Matrix protein underneath membrane
• Helical nuclear capsid of minor strand RNA (HIV has plus strand)
• Seasonal influenza kills between 290 000-600 000 people a year.
  o South Africa: 12 000 deaths per year.
• In pandemic year (new strain we not immune to); kills 250-100 million globally.
• 1918 Spanish flu:
  o Traveled world in a year (By ship and train)
  o 2 waves
  o Arrived in cape town from ships bringing troops home from conflict in Europe
  o Then traveled through south Africa by train – we became 5th worst affected country in world. 300 000 peeps died in SA

Question 16

What is an organism?

Answer 16

“An organism is the unit element of a continuous [genetic] lineage with an individual evolutionary history.”