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36 terms

viruses, viroids, and prions exam 4

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virus origins
transposons, RNA world, don't match any modern cells.
evolution of viruses
1. mutation
2. recombination with each other
3. gene acquisition from bacteria via transduction
intracellular parasites
viruses
are non-cellular
viruses
virus genome
incomplete, only DNA or RNA, no mRNA so no transcription possible
core
where the nucleic acid genome of the virus is contained. DNA or RNA, ss or ds
capsid
houses the core of the virus
provides protection and a way to transmit viral core
composed of proteins arranged as capsomeres
types of capsomeres
1. closed shell
2. helical
3. complex
closed shell
isometric, cubic, polyhedral, or icosahedral
helical
cylindrical capsids
capsids may or may not have
spikes
spikes help to
facilitate absorption to and penetration of host cell
complex capsids
have a combination of helical and closed shell arrangements
envelope
1 phospholipid bilayer, prtein, carbs
2 derived from cell membrane of a previous host cell
3 helps the virus escape host cells as well as penetrate host cells
glycoprotein spikes: types
1. hemagglutinin
2. neuraminidase
hamagglutinin spikes
1. associated with flu viruses
2. facilitate attachment of virus to host cell, binds to sialic acid in host cell membrane
neuraminidase spikes
1. disrupts sialic acid of host cell membrane
2. facilitates flu virus escape from the host cell (release)
virus enzymes
1. bacteriophage - lysozyme
2. HIV - reverse transcriptase, integrase, protease
what will disrupt the envelope?
anything that disrupts cell membranes
what will destroy the capsid?
anything that denatures proteins
what will disrupt the core?
anything that damages nucleic acids
range
represents the different kinds of organisms a virus can infect
specificity
refers to the kind of cells a virus can infect
viral replication: 1. absorption
virus binds to the surface of the host cell using spikes or receptors on its capsid or envelope
viral replication: 2. pentration
1. virus or viral genome enter host cell
2. bacteriophage will release lysozyme to weaken cell well and then inject genome through wall
3. naked animal cell - via endocytosis
4. enveloped animal cell - blends into cell membrane ( envelope fusion)
5. uncoating may occur once inside host cell
viral replication: 3. synthesis
1. viral parts (genomes, capsids) are produced
viral replication: synthesis of DNA viruses (bacteriophages)
1. destroy, inhibit, or lysogenize host DNA
2. use their own viral DNA as tebplate to transcribe viral mRNA
3. use the hosts transfer RNA and ribosome to translate viral mRNA into viral proteins
4. use their DNA as a template for generating more viral cores
viral replication: synthesis of RNA viruses
1. no lysogeny
2. use their genome directly as mRNA that is transcribed by host ibosomes into viral protein
2. use their genome as a template for generating more viral cores
3. positive sense RNA goes directly, negative sense generates complementary copies (more positive sense)
retroviruses
1. use reverse transcriptase to transcribe their RNA into DNA
2. viral DNA uses integrase to lysogenize the host DNA
3. viral DNA transcribe into viral mRNA ---> host ribosome
2 forms of release
1. lysis (naked)
2. budding (enveloped)
viral replication: maturation
virus components are assembled into viruses
viral replication: release
escape of virus from host cell
lysis or budding
cultivation of viruses
in bacterial lawns, plaque formation occurs
plaque
clear zones of lysed cells - viral colony
viroids
collapsed circle of single stranded RNA
attacks other RNA
prions
1. infectious proteins with atypical properties
2. pleated
3. insoluble in water
4. highly resistant to chemicals and heat
5. do not elicit immune response
6. sticky and clump together