Week 1 Flashcards
What are the defining characteristics of a virus?
Non-living entities that contain a nucleic acid genome (DNA or RNA) surrounded by a protein coat +/- lipid envelope.
Don’t contain standard cellular organelles.
Cannot make energy or proteins by themselves- rely on host cell.
Are ALL obligate intracellular parasites.
No genetic capability to multiply by division. Assembly line reproduction.
Define virion.
A complete virus particule that consists of an RNA or DNA core with a protein coat sometimes with external envelopes and that is the extracellular infective form of a virus.
Define virus.
Broad terminology used to describe any aspect of the infectious agent and includes: the infectious (virion) or inactivated virus particle or viral nucleic acid and protein in the infected cell.
Define viroid.
An infectious particle smaller than any of the known viruses, an agent of certain plant diseases. The particle consists only of an extremely small circular RNA molecule, lacking the protein coat of a virus.
Define infectious disease eradication.
Eradication of an infectious disease involved complete elimination of the pathogen or the disease-causing agent from a defined geographic region.
Define pleomorphism.
The ability of some viruses to alter their shape or size
What are the smallest and largest viruses and their range of size?
Smallest- Porcine circovirus type 1 and Parvoviruses- approx 17 nm diameter
Largest- Pandoravirus and Poxvirus- approx 200-400 nm diameter
How do the microscopic methods vary in their ability to determine the morphology of viruses?
Electron Microscopy- Needs negative stain, not detailed.
Cryo-Electron Microscopy- no stain needed, temp dependent, more detail
X-ray crystallography- uses computer graphics, most detailed
Nuclear Magnetic Resonance Imaging
What are the layers of a virus and what are they comprised of?
DNA/RNA genes on the inside.
Capsid surrounds it- made of capsomeres connected by non-covalent bonds.
Lipid envelope surrounds that.
Lipoprotein molecules are like spikes through the lipid envelope.
What type of viruses have a double layer of capsid?
Most viruses have one capsid, except Reoviruses which have a double layer.
What is a nucleocapsid?
Capsid + Virus Nucleic acid (DNA or RNA)/ Genome
What are some characteristics of nucleocapsids with helical symmetry?
Capsomeres and nucleic acid are wound together to form a helical or spiral tube. Incomplete virions (empty helical particles) cannot form.
Naked ones are common among plant viruses, e.g. tobacco mosaic virus.
What are some characteristics of nucleocapsids with cubic/ icosahedral symmetry?
12 corners (vertices/ pentons), 20 facets/ hexons (equilateral triangular faces) and 30 edges Always 12 pentons, but number of hexons varies. Seen in spherical viruses
What is a T-number (aka triangulation number)?
Describes relationship between number of pentagons and hexagons in an icosahedron. Larger T number = more hexagons than pentagons.
h and k are number of jumps from one pentagon to adjacent pentagon across the hexamer.
T = h(squared) + (h x k) + k(squared)
Explain complex symmetry
Virions are composed of several parts, each with separate shapes and symmetries
Pox viruses and bacterial viruses (bacteriophages) both fit in this category
