VIROLOGY 1 - INTRODUCTION TO VIROLOGY

Question 1

why is it important to study viruses?

Answer 1

• make up most of earth’s living matter, influence diversity and evolution
• we carry viral genome as most of our genetic material
• can be harmful to hosts
• can enhance health of hosts
• provide tools and model systems for discovery adn research
• can be engineered to deliver gene therapy and more

Question 2

what is a virus?

Answer 2

genetic element that can multiply only in a living host cell, cannot reproduce independently
obligate intracellular parasite

Question 3

what is a virus particle?

Answer 3

a virion
extracellular form of a virus
exists outside of the host and facilities transmission from one host cell to another

Question 4

when does replication/reproduction of a virus happen?

Answer 4

only upon infection, entry into host cell
causes infections in all living things

Question 5

what do viruses contain?

Answer 5

nucleic acids, either RNA or DNA, no cytoplasmic membrane or organelles

Question 6

what are characteristics of the virion?

Answer 6

protein coat (capsid) that surrounds the nucleic acid
nucleic acid + capsid=nucleocapsid
SOME have a phospholipid:
consists of a phospholipid bilayer from host cell membrane and viral proteins
may possess glycoproteins (spikes) which recognise and bind receptor of host cell
provides protection and recognition site

Question 7

what are characteristics of the intracellular state?

Answer 7

capsid removed
virus exists as a nucleic acid

Question 8

a bit of history of the discovery of viruses

Answer 8

discovered that tobacco mosaic disease was transmissible from plant to plant
discovered that it goes through the filter, means that its extremely small
TMV was isolated characterized and crystallized, nobel prize
found out that viruses could lead to cancer

Question 9

what is the origin of viruses?

Answer 9

still not definitive explanations
either prior to or from cells, but at least 4 billion years ago
viruses required hosts => evolved after cells
or viruses were around during the RNA world, precellular era, where RNA was the sole carrier of genetic information

Question 10

why have viruses appeared?

Answer 10

mechanism to quickly move genes:
viruses facilitate gene host and enrich genetic diversity
especially relevant for prokaryotic cells (horizontal gene transfer)
possible that early viruses cohabitated with host but the evolved to kill it
did they play a role in the RNA to DNA transition?

Question 11

what is the RNA to DNA transition

Answer 11

some RNA viruses evolved DNA genomes to protect them from cellular ribonucleases
DNA is more stable than RNA
they can use the cellular replication machinery to replicate

Question 12

how does climate change affect the spread of human diseases?

Answer 12

climate change drives new encounters between mammal species, which can transmit their diseases to each other
could increase the number of new cases by a lot
58% of infectious disease have been at some point made worse by climatic hazards

Question 13

what are the sizes of viruses?

Answer 13

cannot be seen with a light microscope, you need an electron microscope
range from 20nm to 1000nm (most are 20nm-300nm)
giant viruses are 500nm, as big as many bacteria

Question 14

example of a giant virus?

Answer 14

named mimivirus (mimicks microcbes)
large capsit (400nm) with protein filaments extending 100nm from the surface
large DNA genome that encodes ~1000 genomes (most viruses encode a few)

Question 15

what are large viruses known as?

Answer 15

nucleocytoplasmic large DNA viruses (NLDV)
they can replicate in the host nucleus and cytoplasm

Question 16

how do giant viruses challenge our views of evolution?

Answer 16

only infect eukaryotic unicellular hosts (amoebas, algae and other protists)
genomes are large and diverse
- they may have been small viruses that were experts at stealing genes from host during evolution
hypothesis: some giant virus genes originated from bacteria, archaea, or other viruses and so acquired genes by lateral transfer from bacteria or viruses
they have played a significant role in evolution of eukaryotes through gene exchange

Question 17

what are virophages and what was the first virophage discovered?

Answer 17

virophages are small DNA viruses that replicate only in cell that are co infected with a giant virus
they use the replication factory already established by the giant virus
sputnik was the first variophage discovered, replicated only in mimivirus infected amoeba cells

Question 18

what is the relationship between variophage and co infecting giant virus?

Answer 18

parasitic relationship
for example sputnik reduces mimivirus replication by ~70%
by interfering with the giant viruses they may improve the survival of the host (prevent cell lysis by the giant)

Question 19

what role do viruses play in their ecosystems

Answer 19

help control bacterial populations and influence evolution and diversity of host organism

Question 20

what are bacteriophages (phages)?

Answer 20

viruses that infect and kill bacteria
can be used as phage therapy to combat bacterial infections in humans