Lecture 26: Virology I Flashcards
What is the definition of a virus?
An infectious, obligate intracellular parasite comprising genetic material surrounded by a protein coat (capsid) and, in some cases, a lipid membrane (envelope)
Why are viruses considered as parasites?
Because they need to infect a cell in order to reproduce.
What are glycoproteins?
They are protein spikes embedded in the lipid envelope that some viruses have.
Are viruses alive?
No.
Name 4 reasons why viruses are not considered to be living.
- They do not reproduce on their own.
- They only multiply from the assembly of pre-formed components made in the infected cell.
- They cannot produce ATP on their own
- They are not free-living, as they cannot reproduce outside of a cell.
What are the 2 phases of viruses?
The virion, when it exists in the environment as an infectious particle, and the infected cell.
What is the origin of viruses?
There is not definitive explanation for the origin of viruses, only hypotheses.
Name 3 possible hypotheses for the origin of viruses.
- From mobile genetic elements that gained the ability to move between cells
- From free-living organisms that adapted a parasitic replication strategy
- They may have evolved before cells and led to the evolution of cellular life.
How do viruses replicate?
They replicate by assembly of pre-formed components into many particles. Once in the infected cells, they make the parts and assemble the final product.
How does the growth curve of viruses differ from that of bacteria?
Viruses do not display an exponential growth phase, unlike bacteria.
What are metagenomics?
It is a sequence analysis of genetic material from environmental samples.
What are metagenomics used for?
They can be used to estimate the number of viruses on earth.
Are viruses or bacteria more prevalent?
Viruses outnumber bacteria in every habitat.
How many bacteriophages are present in the world’s waters?
More than 10^30
How much of the species abundance and biomass on living beings do viruses make up?
Abundance: they comprise 94% of species
Biomass: they are small, so they only comprise 5% biomass
Are the majority of viruses pathogenic?
No, most have no impact on our health. But some are, such as herpes.
Explain how climate change impacts viral transmission.
Climate change is expected to bring over 15000 new causes of mammal transmitting viruses to other mammals, as species are moving to cooler locations due to rising temperatures and can interact with other species for the first time.
Name 3 important roles that microorganisms play in marine ecosystems.
- They are the main actors of the global carbon and ocean nutrient cycles
- They promote the regeneration of CO2 and sequestration of CO2 in marine sediments
- They kill 20% of marine biomass each day, particularly harmful algal blooms.
How big are most viruses?
20-300 nm
How does the size of viruses compare to other organisms?
They are smaller than bacteria but bigger than cell organelles.
How can viral pathogens be isolated from bacteria?
Via filtration, as viruses can pass through 0.2 micron filters that bacteria cannot.
What kinds of media can viruses reproduce in?
Only in the host, not in broth (unlike bacteria)
When were the first human virus and yellow fever virus discovered?
1901
When was the rabies virus discovered?
1903
When was the variola virus discovered?
1906
When were chicken leukemia virus and poliovirus discovered?
1908
What was rous sarcoma virus discovered?
1911
When were bacteriophages discovered?
1915
When was influenza virus discovered?
1933
What was the first giant virus discovered and when was it founded?
Mimivirus, discovered in 2003
How big is mimivirus?
400 nm capsid with protein filaments extending 100 nm from the surface.
What phylum do giant viruses belong to?
Nucleocytoviricota.
Giant viruses are also known as […]. Where do they replicate?
Nucleocytoplasmic large DNA viruses (NLDV). They can replicate both in the cell’s cytoplasm and nucleus.
How big are giant viruses compared to bacteria?
They can be just as large as bacteria.
What type of cells can giant viruses infect? Give 3 examples.
Eukaryotic unicellular hosts, such as amoebas, algae, and protists.
What is the hypothesis about the role of giant viruses in evolution?
It is likely that they were small viruses that picked up genes by lateral transfer from bacteria or viruses with an intra-amoebal lifestyle.
What are virophages? What type of genome do they have?
They are small DNA viruses that replicate only in cells infected with a giant virus. They use the viral replication factory established by the giant virus.
The first virophage discovered was called […]
Sputnik.
What is the nature of the relationship between virophages and the co-infecting giant virus?
It is a parasitic relationship. Since viruses interfere with the giant viruses, the virophages can actually improve the survival of the host.
