Lecture 1 Flashcards
Why study viruses?
-Viruses infect all living things
-Viruses are everywhere: outnumbers cellular life 10:1
-We carry viral genomes as part of our own genetic material
-Viruses are important disease-causing agents but not all viruses make you sick
True or false: there are more people on earth than viruses
False: there are more viruses in a liter of costal sea water than there are people on earth
10^31 bacteriophage particles in the ocean
True or false: all viruses are dangerous for us
False: some can be beneficial for us
Viruses catalyse the movement of nutrients from organisms
important players in the regulation of the Earth’s ecology
true or false: viruses can transfer genes between organisms
true
what is the consequence of densovirus on flies
they grow wings
True or false: a virus can’t replace a whole microbiome
false it can in GF mice
What is a virus?
an infecuous, obligate intracellular parasite
what do virus contain?
-genetic material (DNA or RNA)
-Protein coate(capsid)
-In some cases, an envelope (lipid bilayer) derived from host cell membranes
True or false: all viruses go through filters
False: we discovered viruses that are so big like the mimivirus that does not go through the usual filter
usually they are in nm
True or false: we have early recordings of viruses
yes we have dating from egyptians
What are the 3 hypotheses for where viruses come from?
-The virus-first hypothesis
-the regressive or reduction hypothesis
-the progressive or escape hypothesis
What is the virus first hypothesis
Viruses predate or coevolved with their current cellular hosts
What is the regressive hypothesis
Viruses are remnants of cellular organisms (“fourth domain”)
What is the progressive hypothesis?
viruses arose from genetic elements that gained the ability to move between cells
Why are viruses considered as inanimate?
They exist in 2 phases: an inanimate: the virion and a multiplying phases in the infected cell
-viruses are passive: they are completely at the mercy of their environments. They can’t synthesize, exhibit, display, destroy, evade and generate on their own
When was electron mucroscopy first discovered?
1930’s
What are the 4 things we use to classify a virus?
-nature and sequence of nucleic acid virion
-symmetry of protein shell (capsid)
-Presence or absence of a lipid membrane aka envelope
-dimensions of virion and capsid
What are the 4 classes we use in the hierarchal system?
-Order (virales)
-Family (viridae)
-Genus (virus)
-Species
Protovirology
Before viruses were recognized
1796-1885
-1978 cowpox lesions used to vaccinate against smallpox: Jenner
-1882 transmission of tabacco mosaic disease with cell free extracts: Mayer
-1885 devlopment of rabies vaccine : Pasteur, Roux
Auroravirology
The dawn of virology
1892-1933
-1892 Description of a ‘filterable infectious agent’ (Ivanovsky)
-1898: Concept of a ‘virus’ as a contagious element (Beijernick)
Discovery of 1st animal virus:
Foot-and-mouth-disease virus, FMDV(Loeffler, Frosh)
-1901 Discovery of 1st human virus: Yellow Fever Virus, YFV (Reed)
-1911 Discovery of first solid tumor virus (Rous)* nobel prize
-1913 Virus Cultivation in tissue culture (Steinhardt, Lambert)
-1915 Discovery of bacterial viruses: Bacteriophages (Twort, d’Hérelle)
Meridiovirology
Midday, the sequel to dawn (classic virology)
1934-1955
-1934 Bacteriophages are composed of protein and nucleic acids
(Schlesinger)
-1935 Crystallization of Tobacco Mosaic Virus, TMV (Stanley)* Nobel prize
-1938 Yellow Fever Virus (YFV) vaccine (Theiler)*
Electron Microscopy is used to image viruses (von Borries, Ruska, Ruska)
-1943: genetic origins of mutations (Luria, Delbreck) *
-1952 plaque assay of an animal virus, poliovirus (Dulbecco)*
Viral genomes are composed of nucleic acids (Hershey, Chase)*
Janovirology
Names for the gods of endings and beginnings
1956-1975
-1956 Virus particles are composed of identical subunits(Watson, Crick)
RNA can carry genetic information
(Schramm, Fraenkel-Conrat,Williams)
-1962 Studies of virus structure (Klug, Caspar)*
-1967 DiscoveryofViroids(Diener)
Discovery of Hepatitis B virus (Blumberg)*
-1970 Discovery of Retroviral Reverse Transcriptase (Temin, Baltimore)*
-1972 1st Recombinant DNA molecules (Berg)*
-1973 1st restriction Map (Nathans) *
Neovirology
Dominated by viral sequence information
1976-
- Neovirology (1976 - Present)
Dominated by viral sequence information
-1976 1st RNA genome sequenced (Fiers)
-1977 1st DNA genome sequenced (Sanger, Fiers, Weissman
Discovery of RNA splicing (Roberts, Sharp)*
Discovery of tumor suppressor p53 (Levine, Crawford)
1st virus crystal structure (Harrison)
-1978 1st infectious molecular clone of an RNA virus (Weissman)
-1981 1st infectious molecular clones of
animal viruses (Baltimore)
-1982 1st Antivirals (Elion, Hutchings)*
-1983 Discovery of Human Immunodeficiency Virus (Montagnier, Barre-Sinoussi, Gallo)
-1989 Discovery of Hepatitis C Virus* (Alter, Houghton, & Rice)
-1998 Discovery of Gene Silencing (Fire, Mello)*
What are all the steps to the infectious cycle?
-Binding to cell receptor
-entry and uncoating its genome so that it’s ready for early gene expression
-Early gene expression
-replication of viral genome
-late gene expression
-assembly of virions
-exit
True or false: viruses are not cell specific
false: it is cell tissue/type specific
Virus-encoded proteins of the virion bind to specific proteins, carbohydrates or lipids on the cell surface
Viruses must recognize and bind to the cells that they infect
-Cellular receptors are specific for each virus and host species (which can determine tropism)
How do viruses enter the cell after receptor binding?
Once they have located the appropriate cell, they must pass through the cell wall or membrane(s):
- Bacteriophages have special tails that drill holes and inject their genome into the host cell
- Plant viruses often penetrate as a result of damage to the cell wall
- Animal viruses are taken up into the cytoplasm via membrane fusion or endocytosis
Once inside the cell, the capsid disintegrates to release the genome aka uncoating
Early gene expression
-The viral genome must direct expression of early proteins: typically regulate genome replication
-Molecular pathway to early gene expression (production of viral mRNA) depends on the chemical nature and strandedness of the viral genome aka DNA or ran, ds or ss and etc
True or fa;se: during replication of the viral genome, early proteins promote replication of the viral genome and the infected cell becomes a factory for the expression and replication of viral genomes
True
true or false: late viral proteins are typically non-structural proteins
false: they are structural proteins used to make viral particles
Assembly of virions
-Structural proteins package viral genomes and assemble the capsid
-Enveloped viruses encode glycoproteins that are inserted into lipid membranes and direct formation of the viral envelope upon release
what is the most abundant viral protein made?
The structural proteins
Exit of the virus
Progeny virions are released from the host cell
-Death and lysis of the host cell
-Extrusion from the cell membrane (budding)
Virions find and infect new host cells and reinitiate the replication cycles
Viruses replicate by…..
assembly of pre-formed components into many particles
What happens when you infect all the cells vs a few cells
you get a huge burst when you infect all vs small bursts when you infect a few
True or false: not all viruses have to make mRNA
false they all have to make mRNA that can be translated by host ribosomes
