VIROLOGY 1 - INTRODUCTION TO VIROLOGY Flashcards
why is it important to study viruses?
- 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
what is a virus?
genetic element that can multiply only in a living host cell, cannot reproduce independently
obligate intracellular parasite
what is a virus particle?
a virion
extracellular form of a virus
exists outside of the host and facilities transmission from one host cell to another
when does replication/reproduction of a virus happen?
only upon infection, entry into host cell
causes infections in all living things
what do viruses contain?
nucleic acids, either RNA or DNA, no cytoplasmic membrane or organelles
what are characteristics of the virion?
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
what are characteristics of the intracellular state?
capsid removed
virus exists as a nucleic acid
a bit of history of the discovery of viruses
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
what is the origin of viruses?
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
why have viruses appeared?
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?
what is the RNA to DNA transition
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
how does climate change affect the spread of human diseases?
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
what are the sizes of viruses?
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
example of a giant virus?
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)
what are large viruses known as?
nucleocytoplasmic large DNA viruses (NLDV)
they can replicate in the host nucleus and cytoplasm
how do giant viruses challenge our views of evolution?
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
what are virophages and what was the first virophage discovered?
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
what is the relationship between variophage and co infecting giant virus?
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)
what role do viruses play in their ecosystems
help control bacterial populations and influence evolution and diversity of host organism
what are bacteriophages (phages)?
viruses that infect and kill bacteria
can be used as phage therapy to combat bacterial infections in humans
