Introduction to Viology

Question 1

Where can we find viruses?

Answer 1

• they are everywhere
• everybody has had a viral infection
• virus infect all living things

Question 2

What is the relationship between our genetic code and viral genomes?

Answer 2

• we have viral genetic sequences integrated into our own genetic material
• about 10% of our DNA is derived from retroviruses

Question 3

What are endogenous retroviruses?

Answer 3

• found in the host germline
• endogenous viral sequences are remnants from infections that occurred millions of years ago but are no longer infectious

Question 4

What are exogenous retroviruses?

Answer 4

• found in the host stomatic cells

Question 5

What are the 3 levels of defence mechanisms?

Answer 5

• intrinsic
• innate immunity
• acquired immunity
• pathogens which pass acquired immunity can be deadly

Question 6

What is the story with wasps and caterpillars?

Answer 6

• wasps lay their eggs inside a living insect larva
• when female wasp deposits eggs inside a caterpillar, she also deposits her polydnavirus genome sequences
• the innate immune system of larva would normally kill the egg, preventing its development
• wasp genes carried by the polydnavirus genome suppress this innate immune response

Question 7

What is the story about a virus that helps a fungus?

Answer 7

• dichanthelium lanuginosum (plant) grows in geothermal soils at temperatures over 50C
• fungus Curvularia protuberate permits plant survival
• however, the fungus cannot grow at higher temperatures
• fungal thermotolerance is mediated by the curvularia thermal tolerance virus

Question 8

What is the story about a virus that makes nice flowers?

Answer 8

• tulipomania - the first documented economic crisis
• Holland in the 1600s experienced an economic uprising
• freedom from Spain and bubonic plague increases wages in survivors
• the dutch spend 3000 guilders for broken tulip
• tulips are purchased in advanced leads to a high speculative market
• by mid-1600s, tulip market crashed - many people are bankrupt
• potyvirus - tulip breaking virus (TBV) results in the pattern
• TBV interferes with the synthesis of pigments in the flowers

Question 9

What is needed in order for viruses to survive?

Answer 9

• package their genome inside a particle
• use this particle to transfer their genome from host to host
• the genome contains information to initiate and complete the viral infectious cycle
• genomes establish themselves in host ensuring long term viral survival
• genome is key
• viral genomes are obligate molecular parasites
• they can only function after they replicate in a host cell
  0 viruses must make mRNA that can be translated by host ribosomes
• thus they use the host protein synthesis machinery to make viral proteins
• no virus can translate proteins from mRNA on their own

Question 10

What is the importance of virology

Answer 10

• viral-host interactions have increase our knowledge of how the host functions

Question 11

Viruses are not smart…

Answer 11

• they just replicate and make a lot of everything
• they do not grow
• creation of mutants
• some mutants survive

Question 12

Darwin: survival of the fittest

Answer 12

• viruses need the host in order to survive

- need balance

Question 13

Beginnings of virology

Answer 13

• viruses existed in the dinosaur age
• they have most likely existed for over 250 million years
• the use of molecular clocks sequencing techniques have enabled such affirmations

Question 14

Documented beginnings of virology

Answer 14

• Ancient Greeks - described an ailment that they termed “Herpes” or “to creep or to crawl”
• due to moving lesions on the skin
• Ancient Greeks - Emperor Tiberius banned kissing in public to avoid transmission of herpes

Question 15

Tobacco mosaic virus

Answer 15

• the late 1800s
• crash TMV infected leaves and filter them
• an agent in the filtrate could be rubbed on a new leaf and infect once again
• the agent could not “grow” on its own
• filtration results differ from bacteria which are not infiltrate
• the “growth” is different fro bacteria which do not require a host

Question 16

First animal virus

Answer 16

• discovered in 1898 by Loeffler and Frosch
• discovered as an ‘agent’ causing foot and mouth disease and being filterable
• viruses can be filtered through a 0.2-micron filter (not always though)

Question 17

How can we see them?

Answer 17

• electron microscopy and modern structural biology has allowed virologists to observe the complexity of viruses

Question 18

What are mimiviruses?

Answer 18

• can be seen under a light microscope
• do not pass through a 0.2-micron filter
• host is Amoeba