15. Virology I: Introduction to Viruses Flashcards
what are viruses?
- 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
how do viruses replicate
-obligately replicate inside host cells
- use host etabolic machinery and ribosomes
what do viruses form, and what are the functions?
- a pool of components
- assemble into virions (particles)
- protect the genome
– and transfer it into other cells
what are the simple definitions of viruses?
-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.
how big are viruses?
- bacterial
– 1 micron - lambda phage
– 0.1 micron - animal cell
– 10 micron
what do viruses consist of?
- acellular
- genetic material core
– DNA / RNA enclosed by coat of proteins - enveloped viruses (animal viruses)
– enclosed by lipid envelope
how are viruses classified and reproduce?
- reproduce in living cells
- classified:
– nucleic acid characteristics
– capsid symmetry
– host
– diseases caused
what are the structural differences between non-enveloped / enveloped viruses?
- capsomers / envelope
- nucleocapsid
– nucleic acid / DNA, RNA
– capsid composed of capsomers / capsid
why are viruses considered as dead?
- don’t:
– metbolise
– have cells
– reproduce independently
how do viruses not replicate independently?
- inert packages of nucleic acid
– can’t replicate without host cell
what traits define viruses as living?
- made of same building blocks
- replicate and evolve
- inside cell, they engineer environment suitably
how are viruses non-living / living?
- alternate between inactive state (out of cell) and living
- metabolically active sate (inside cell)
– virocell
why are viruses important?
- greates biodiversity on earth
- drive global cycles
- beneficial
- pathogens
how do viruses drive global cycles?
- carbon, nitrogen, sulphur cycles
- facilitate genetic transfer between different cell types
how are viruses beneficial?
- control of pests
how are pathogens caused by viruses important?
- main cause of death and illness
what are the abundances of organisms?
- biomass:
– mostly prokaryotes
– 5% viruses
– least protists - abundance:
– 94% viruses
– prokaryotes
– least protists
why are we not always infected?
- 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
how do we classify viruses?
- nature and sequence of nucleic acid encapsidated
- symmetry of capside (protein shell)
- presence / absence of envelope (lipid membrane)
- dimensions of virion and capsid
what rule do viruses follow?
- viral genomes make mRNA ably read by host ribosomes
what terminology is used with DNA and RNA?
- DNA:
– single stranded
–double stranded - RNA:
– single stranded
– double stranded
what are the differences between single and double stranded RNA / DNA?
- 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
draw the diagram of retro/DNA/RNA viruses
-
what are the main components of the human genome?
- 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%)
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
draw retrovirus infection and reverse transcription
-
coronaviruses
-
what are the discrete virus phases?
- virion
– infectious particle - infected cell
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)
draw the replication graph of a virus
-
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)
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
