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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


are non-cellular


virus genome

incomplete, only DNA or RNA, no mRNA so no transcription possible


where the nucleic acid genome of the virus is contained. DNA or RNA, ss or ds


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


cylindrical capsids

capsids may or may not have


spikes help to

facilitate absorption to and penetration of host cell

complex capsids

have a combination of helical and closed shell arrangements


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


represents the different kinds of organisms a virus can infect


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)


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


clear zones of lysed cells - viral colony


collapsed circle of single stranded RNA
attacks other RNA


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

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