Lec 2: Structure Flashcards
Viral components: (3)
- ) nucleic acids
- ) capsid
- ) envelope (if enveloped)
(+)RNA –>
(-)RNA –>
(+)RNA –> can be directly used to synthesize protein
-)RNA –> compliment to (+
viroid =
small, self-replicating ss circular RNA molecule w/o protein coat
viroids are the smallest
infectious pathogens known
ALL known viroids…
infect higher plants
viroids often transmitted (2)
mechanically
& through pollen and seed
genome is packages in a protein structure known as a
capsid
many viruses also have a
which…
lipid component
which are generally present @ the surface of the virion forming an envelope (which also contains proteins with roles in aiding entry into host cells)
a few viruses form
protective protein occlusion bodies around their virions
Function of Viral Capsids: (2)
- ) protect viral genome
2. ) aid in entry of virus to a host cell
Naked virus structure:
capsid + genome = virion
Other viruses structure:
nucleocapsid =
(outer layer protein sometimes) + lipid envelope + capsid + genome = virion
nucleocapsid = capsid + genome
5 types of viral structure:
Icosahedral Enveloped Icosahedral Helical Enveloped Helical Complex
Virus genomes: (7)
*note:
ss, linear DNA
ds, linear DNA
ss, circular DNA
ds, circular DNA
ss, linear RNA
ds, linear RNA
ss, circular RNA
*note: NO ds circular RNA viral genome discovereed yet
How are virus genomes packed?
- Some viruses:
- Many viruses:
- Some capsid proteins:
- Some viruses: capsid protein coats the genome
- Many viruses: nucleic acids bind inner part of capsid protein non-covalently (anchors DNA/RNA w/in capsid to avoid free-floating)
- Some capsid proteins: have regions such as zinc finger that binds to nucleic acids
Human genomes =
Viral genomes =
chromosomes
segmented
most viruses consist of
but some…
a single molecule of nucleic acid
…but some have genes encoded in 2 or more nucleic acid molecules = segmented
segmented genomes are more common in
RNA viruses than DNA ones
some viruses package genome segments into…
while others package genome segments into…
one virion (ex: influenza virus) separate virions (ex: brome mosaic virus)
Brome Mosaic Virus contains…
3 types of particles that are physically & virtually indistinguishable:
- ) most dense (RNA1)
- ) least dense (RNA2)
- ) middle density (RNA3 & RNA4)
Why is segmentation favorable? (3)
but…
1.) allows virus to survive environmental pressure
2.) more potential for gene recombination
3.) faster evolution
…but for those who package genome into separate virion, at least one of each has to infect the same cell
(Capsid proteins)
Simple Virus =
Complex Virus =
= 1 protein type for capsid
= multiple protein types for capsid
capsid proteins are…
asymmetrical, but are organized to form symmetrical structures
many _____ viruses have helical symmetry
ssRNA