15. Virology I: Introduction to Viruses Flashcards
1
Q
what are viruses?
A
- acellular organisms
- genomes consist of nucleic acid
- obligately replicate inside host cells
– using host metabolic machinery and ribosomes - form pool of components assembling particles (virions)
– protect the genome and transfer it to other cells
2
Q
how do viruses replicate
A
-obligately replicate inside host cells
- use host etabolic machinery and ribosomes
3
Q
what do viruses form, and what are the functions?
A
- a pool of components
- assemble into virions (particles)
- protect the genome
– and transfer it into other cells
4
Q
what are the simple definitions of viruses?
A
-Viruses are acellular organisms with nucleic acid genomes, which make particles to protect the genome and transfer it between cells.
- An infectious, obligate intracellular parasite comprising genetic material (DNA or RNA) surrounded by a protein coat and/or a membrane.
5
Q
how big are viruses?
A
- bacterial
– 1 micron - lambda phage
– 0.1 micron - animal cell
– 10 micron
6
Q
what do viruses consist of?
A
- acellular
- genetic material core
– DNA / RNA enclosed by coat of proteins - enveloped viruses (animal viruses)
– enclosed by lipid envelope
7
Q
how are viruses classified and reproduce?
A
- reproduce in living cells
- classified:
– nucleic acid characteristics
– capsid symmetry
– host
– diseases caused
8
Q
what are the structural differences between non-enveloped / enveloped viruses?
A
- capsomers / envelope
- nucleocapsid
– nucleic acid / DNA, RNA
– capsid composed of capsomers / capsid
9
Q
why are viruses considered as dead?
A
- don’t:
– metbolise
– have cells
– reproduce independently
10
Q
how do viruses not replicate independently?
A
- inert packages of nucleic acid
– can’t replicate without host cell
11
Q
what traits define viruses as living?
A
- made of same building blocks
- replicate and evolve
- inside cell, they engineer environment suitably
12
Q
how are viruses non-living / living?
A
- alternate between inactive state (out of cell) and living
- metabolically active sate (inside cell)
– virocell
13
Q
why are viruses important?
A
- greates biodiversity on earth
- drive global cycles
- beneficial
- pathogens
14
Q
how do viruses drive global cycles?
A
- carbon, nitrogen, sulphur cycles
- facilitate genetic transfer between different cell types
15
Q
how are viruses beneficial?
A
- control of pests
16
Q
how are pathogens caused by viruses important?
A
- main cause of death and illness
17
Q
what are the abundances of organisms?
A
- biomass:
– mostly prokaryotes
– 5% viruses
– least protists - abundance:
– 94% viruses
– prokaryotes
– least protists
18
Q
why are we not always infected?
A
- most viruses pass through us
– ingest many non-animal viruses with food - example:
– leafy vegetables (cabbage) contaminated with baculoviruses
– 100 cm2 of leaf material contain 10*E8 particals of virus pathogenic for cabbage looper
19
Q
how do we classify viruses?
A
- nature and sequence of nucleic acid encapsidated
- symmetry of capside (protein shell)
- presence / absence of envelope (lipid membrane)
- dimensions of virion and capsid
20
Q
what rule do viruses follow?
A
- viral genomes make mRNA ably read by host ribosomes
21
Q
what terminology is used with DNA and RNA?
A
- DNA:
– single stranded
–double stranded - RNA:
– single stranded
– double stranded
22
Q
what are the differences between single and double stranded RNA / DNA?
A
- single stranded:
– linear / circular DNA
– linear +ve / linear -ve / linear segmented RNA - double stranded:
– linear / linear with single chain breaks / circular DNA
– linear segmented RNA
23
Q
draw the diagram of retro/DNA/RNA viruses
A
-
24
Q
what are the main components of the human genome?
A
- introns (26%)
– protein coding genes (1.5%)
– dispersed by non-coding introns - LINEs (20%)
- SINEs (13%)
- miscellaneous unqiue sequences (12%)
- LTR retrotansponsons (8%)
- miscellaneous heterochromatin (8%)
– remnants of retroviruses (fossil relics of former viral infections) - segmental duplications (5%)
- DNA transposons (3%)
- simple sequence repeats (3%)
25
what are retroviruses?
- type of RNA virus
-- inserts copy of genome into DNA of host cell (changing genome of cell)
- achieved through reverse transcriptase
-- many errors made: non-infectious/attenuated virions or more infections virions)
- virions consist of enveloped particles (100 nm diameter)
-- obtained from host plasma membrane during budding process
- virions contain two identical single-stranded RNA molecules
26
draw retrovirus infection and reverse transcription
-
27
coronaviruses
-
28
what are the discrete virus phases?
- virion
-- infectious particle
- infected cell
29
what is the mimivirus?
- Acanthamoeba polyphaga mimivirus (APMV)
- isolated from amoebal co-culture present in a water sample from cooling tower
- characteristics:
-- DNA virus
-- 700 nm diameter
-- genome approxiamately 1.2 MB (million base-pairs)
- structure:
-- fibrils
-- capsid
-- inner membrane
-- core
- core:
-- dsDNA virus
-- 90% coding capacity
-- 10% junk DNA
-- 1.2 MB
-- 911 protein coding genes
-- additional genes (aminoactyl tRNA synthetases; sugar; lipid; amino acid metabolism)
30
draw the replication graph of a virus
-
31
what is the pandoravirus
- pandoravirus salinus
-- from mouth of Chile's Tunquen River
- pandoravirus dulcis
-- freshwater pond near Melbourne
- parasitize amoebas
- sizes
-- 1 micrometer in length
-- dwarfs: 50 - 100 nm
- supersize DNA
-- 2500 genes (compared to 10 in many viruses)
32
what is the pithovirus?
- Pithovirus sibericum
-- zombie virus
- 1.5 micrometer length, 0.5 micrometer diameter
- 500 genes
- over 30 000 years in ancient permafrost
-- when exposed to host (amoebas), still active and quickly infected host
- giant viruses:
-- very tough,
-- special environments (deep ocean sediments, permafrost - preserve microbes, viruses)
- climate change exposes potential viruses in ancient ice
