Viruses and Prions Flashcards
Reasons to Study Viruses?
-major source of disease
-limited anti-viral therapies
-One Health
What % of human viral infections have an animal origin?
70%
3 Components of the Definition of a Virus
- Obligate intracellular parasite (needs host cell)
- Submicroscopic (filterable) infectious agent
- Possess genetic material
Viral Small Size Exception
Megavirus from Chile was HUGE (1.2 million base genome)
Viral Genetic Material Exception
prions (do not contain nucleic acids)
Definition of Life
capacity to maintain an electrochemical gradient across a membrane (make ATP)
Are viruses living or non-living?
non-living
Do viruses have any biologically active membranes?
no
Modified Live Virus vs. Inactivated/Killed Virus Vaccine
modified live is still replication content versus killed are chemically inactivated
but NEITHER is living!
Envelope vs. Membrane
an envelope is non-living and does not function metabolically (despite being derived from the host cell)
3 Functions of RNA
- Can fold into complex structures
- Perform enzymatic activities (self-cleaving)
- Contain genetic information
Why is it thought that RNA-based organisms were the first “proto-life” forms?
you can find genes in modern RNA viruses that you can’t find anyplace else - evolutionary remnants
Koch’s Postulates
Polymicrobial Syndromes
“Death by a Thousand Cuts”
you’re not typically chasing after one big deadly virus, but it’s multiple things
The structure and physical composition of a virus provides essential information on what five things?
- Identification
- Pathogenesis
- Diagnosis
- Treatment
- Prevention
identification
how to classify it
pathogenesis
how it causes disease
diagnosis
how to detect it
treatment
how to control it
prevention
how to keep it out
2 Possible Virus Structures
- Non-enveloped
- Enveloped
Layers of a Non-Enveloped Virus
- Protein Capsid
- Nucleic Acid Genome
Layers of an Enveloped Virus
- Lipid envelope
- Protein capsid
- Nucleic Acid Genome
Where do enveloped viruses get their envelope from?
host cell membranes (nuclear, ER, Golgi, plasma)
Whose proteins are embedded in the lipid envelope - host or viral?
BOTH
capsid protein subunits
capsomeres, nucleocapsid proteins, nucleoproteins
Why is a capsid considered a “minimum structure?”
it is made to be the SMALLEST surface area that can encase a MAXIMAL volume
Why does a capsid need to be stable?
protects the nucleic acid genome
Why does a capsid need to be unstable?
it will need to be disassembled to allow the release of nucleic acid during replication
2 Protein Capsid Shapes
- Symmetrical
- Complex
2 Symmetrical Capsids
- Icosahedral
- Helical
Icosahedral Capsid
soccer ball, EPCOT
Helical Capsid
cylindrical with capsomeres arranged in a “spiral staircase” pattern around the genome
ex: rhabdovirus (rabies)
Complex Capsid
no symmetry, an absolute mumbo jumbo or nuclear proteins and nucleic acids
Two Types of Proteins in the Lipid Bilayer of the Virus Envelope
- Surface Glycoproteins
- Integral/Matrix Proteins