CH6 pt 1 Flashcards
scientists that said viruses are filterable agents
- Ivanovski and Beijernick (cumberland filters)
- Reed (yellow fever)
- non-cellular, infectious entities that have genome DNA or RNA, evolve, reproduce themselves in living cells and require a host
- filterable agents
- mature infectious particle
viruses
mature infectious particle that have central core of nucleic acid, capsid, and +
virion
- protein coat that are mostly in the icosahedral or helical form
- proteins (protomers) in clusters (capsomers)
- many have tails attached
capsid
describe nucleic acids in viruses
- packed inside capsid
- dsDNA, dsRNA, ssDNA, ssRNA
- circular or singular
- single or in pieces (segmented
- few to several hundred genes
- phospholipid/ protein membrane
- “stolen” form host cell
- fusion (host cell entry); sensitive to environment/chemical/temp
envelope
- glycoprotein
- for attachment
spikes
- RNA polymerase
- reverse transcriptase (retroviruses)
enzymes
describe the replication of a virus
- attachment of virion to host cell
- entry of viral nucleocapsid
- synthesis of viral proteins and nucleic acids
- self-assemby of virions
- release of progeny virons
how does a virus attach/absorb to host cell?
specific receptors on host cell
-ex: HIV will only effect if CD4 receptors present
vectors: insects or fungi
plant viruses
- inject nucleic acid
- capsid remains outside, never goes in host cell
bacteriophage
- fusion of host cell membrane with virus envelope
- engulfed in membrane bound vesicles (endocytosis)
- capsid digested to free nucleic acid (cytoplasm, nucleus, vesicle)
animal viruses
three types of animal virus into host cells
- entry of enveloped virus by fusing with plasma membrane
- entry of enveloped virus by endocytosis
- entry of non-enveloped virus by endocytosis
describe the entry of enveloped virus by fusing with plasma membrane
- viral envelope spikes bind to receptors on surface of host cell
- lipid bilayer of viral envelope fuses with host cell membrane
- nucleocapsid is released into cytoplasm of the host cell
describe entry of enveloped virus by fusing with plasma membrane
- viral envelope spikes bind to receptors on surface of host cell
- vesicle forms in cell, binding to the receptor triggers receptor- mediated endocytosis in endosome
- increased acidity allows nucleocapsid to escape from the endosome and enter the cytoplasm
describe entry of non-enveloped virus by endocytosis
- capsid proteins bind to receptors on cell surface and trigger receptor- mediated endocytosis
- nucleic acid is extruded from the endosome into cytoplasm
-sequence/pathway depends on genome
virus synthesis
describe DNA and ssRNA synthesis
- DNA–>mRNA synthesis–> proteins
- ssRNA–>dsRNA–>provirus in host chromosomal–>mRNA synthesis–>proteins
name early and late proteins of virus synthesis
- early- taking over host cell (polymerase, regulatory proteins)
- late- structural proteins (capside, spikes, cell lysis)
two most common virion release
- lysis of host cell-naked virus
- budding- enveloped virus
genomes or nucleocapsids of many plant viruses also move directly from cell to cell through small connections that link to adjacent cells
plasmodesmata
mechanism for releasing enveloped virions
- viral envelope proteins are inserted into host cell’s plasma membrane. The viral matrix protein lines the cytoplasmic face of the plasma membrane
- nucleocapsids are directed to the plasma membrane by host cells microtubules
- plasma membrane protrudes outward and nucleocapsids are surrounded by matrix lined plasma membrane (budding virion)
- neck of protruding membrane is pinched off and a mature virion is released
