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Transcript of Viruses
", which comes from their habit of "eating" lawns of bacteria on petri dishes.
There are 10 phages on the planet*
Since they can not carry out their life cycle independent of a host cell (as they are not made of cells), viruses are not traditionally considered to be alive...
...as if it matters
What a Virus is:
An "Obligate Intracellular Parasite"
Viruses consist of:
A protein coat ("
"A piece of bad news, wrapped in a protein"
-Sir Peter Medawar (virologist)
Viruses were first discovered by Dmitri Ivanovsky who was studying the transmission of Tobacco Mosaic Disease.
Something smaller than cells was causing the disease.
Since then, viruses for all domains of life have been discovered. Many are harmless, some are quite deadly.
What a Virus isn't
2 Kinds of Phages
The "lytic" Cycle
"Classic" viral life-cycle
Infection, synthesis, assembly, lytic release
Assembly is auto-catalytic
- the "lunar lander"
The "lysogenic" Cycle
Phage DNA splices in to bacterial chromosome.
When cell replicates, phage DNA is replicated, too.
Can go lytic as conditions dictate.
Treatment of bacterial diseases using phages.
Phages are species specific to bacteria.
Has been used for ~80 years (just not really in the US)
A "new" avenue of research (why?)
Eukaryotic viruses are more diverse than phages:
DNA or RNA genomes. Single stranded or double stranded.
Many have a
that surrounds the protein coat.
2 Example Animal Viruses
An RNA virus
Easily transmitted in aerosol form
Responsible for more deaths in human history than any other known virus
Mutates rapidly ("
"), so permanent immunity is not possible.
Human Immuniodeficiency Virus
The genome is RNA.
The virus has a code for "
Reverse transcriptase makes a DNA copy of the genome, which is then spliced into the host cell chromosome.
RNA to DNA = Central Dogma "violation"!
Accute infection is kind of like flu symptoms
As the virus destroys immune system cells, the body becomes prone to "
" (this is called
The virus can only be spread through bodily fluid exchange.
There are various treatments, which are primarily available in the developed world.
Plants get viruses, too.
They typically manifest as "blotchy" pigment patterns.
are not the
Disease causing RNA molecules in plants.
Do not code for protein.
Disease causing protein molecules
Have no genetic material.
Cause BSE (cows), CJD (humans), scrapie (sheep), CWD (deer)
Make Sure You Can:
What is a virus?
How does a virus function?
Explain why viruses could be considered living or non-living depending on particular aspects of their function.
Explain how different types of viruses utilize the information system of cells to complete their life cycles.
Compare bacteriophages and eukaryotic viruses.
Compare the lytic and lysogenic cycles of bacteriophages.
Explain why some eukaryotic viruses have RNA genomes.
Explain the features of the viral life cycle of a typical DNA, RNA and retroviral eukaryotic virus.
Explain the consequences of viral life cycles on human health.
Explain the relationship between HIV and AIDS in terms of causes, effects and treatments.
Compare viruses to other infectious particles that have been described by science.
The Herpes Virus
Tobacco Mosaic Virus
Phage infection plaques on a bacterial lawn
* this is a larger number than the number of stars in the Universe. If you lined them all up, they would make a line 100 million light years long.
Phage plaque on a colony of
Co-infection by 2 flu strains can trigger large-scale viral recombination
Timeline showing the major flu viruses present in the human population
Naming conventions for flu viruses
(H- hemagglutinin, N- neuraminidase)
A sample of drugs that an HIV positive individual may take. The drugs work to interfere with viral replication.
This one drug costs ~$1200 a month
The AIDS Quilt is now too large to be displayed in one piece.
HIV entering and leaving a Helper T-Cell.
RNA Sequence of a potato viroid
Characteristic "spongiform plaque" in brain tissue of a person with BSE (aka "mad cow disease")
Cover your Mouth!
Spread by Aedes mosquitoes (Aedes aegypti)
Major outbreak in Brazil and Latin America
Linked to birth defects (microcephaly)