Viruses and prions
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what are viruses?
protein and nucleic acid
what are viroids?
- only RNA
- (circular ss RNA)
what are satellites?
- DNA or RNA only
- do not encode their own vapid proteins
- require a helper virus to replicate
- encode one or more gene products
what are Prions?
what are the steps for disease production by prions
- 1.abnormal prions interacts with normal protein
- 2.normal protein is converted into the abnormal protein
- 3. continued conversion of normal proteins until there is no more normal proteins
what is viruses role in evolution?
transfer genes between bacteria/ other organisms
what are the general properties of irons?
- consists of >1 molecule of DNA or RNA enclosed in a coat of protein
- may have additional layers
- cannot reproduce independent of living cells
what is the virion size range?
10 to 400 nm
what is a capsid?
- large macromolecular structures which serve as protein coat for the virus
- It protects the viral genetic material and aids in its transfer between host cells
what are the protein subunits of capsids?
what are the different shapes of capsids?
- helical - hollow tubes with protein walls
- icosahedral - regular polyhedron with 20 equilateral faces and 12 vertices
what is the outer flexible membranous layer in a virus called?
what are the function of viral envelope proteins?
- viral attachment to host cell
- identification of virus
- enzymatic activity
- may play a role in nucleic acid replication
where are most virion enzymes located?
within the capsid
what are the steps for viral multiplication?
- attachment to host cell
- uncoating of genome
what are the 3 methods used for uncoating of the genome?
- fusion of the viral envelope with host membrane; nucleocapsid enters
- endocytosis in vesicle; endosome aids in viral uncoating
- injection of nucleic acid
what must a RNA viruses carry in/synthesize to complete synthesis?
how are proteins assembled for viral multiplication?
- some are assembled in the nucleus
- some are assembled in the cytoplasm
how are non enveloped viruses released from the cell?
nonenveloped viruses lyse the host cell by attacking the peptidoglycan membrane
how are enveloped viruses released from the cell?
enveloped viruses use budding to merge with the host cell membrane and then are exocytosed
what are the 2 reproductive options for temperate phages?
- 1. reproduce lytically as virulent phages do
- 2. remain within host cell without destroying it
what is a prophage?
phage that integrates their genome into the host genome
what is a lysogenic relationship?
virus does not replicate in bacteria with genes integrated into the genome
what are the 2 advantages to lysogeny for a virus?
- phage remains viable but may not replicate
- multiplicity of infection ensures survival of host cell
why does temperate phage chafes the phenotype of its host
- bacteria become immune to superinfection
- phage may express pathogenic toxin or enzyme
when does a cell undergo induction?
induction occurs when conditions in the cell cause the prophage to initiate synthesis of new phage particles
what is neoplasia?
abnormal new cell growth and reproduction due to loss of regulation
what is anaplasia?
reversion to a more primitive or less differentiated state
what is metastasis?
spread of cancerous cells throughout the body
what are the possible mechanisms by which viruses causes cancer?
- viral proteins bind host cell tumor suppressor proteins
- carry oncogene into cell and insert it into host genome
- altered cell regulation
- insertion of promoter or enhancer next to cellular oncogene
what are cytopathic effects (CPE)
degenerative changes or abnormalities in host cells/ tissues because of viral infection
what are plaque assays used for?
to visualize the presence of a virus
what are the 2 types of plaque assays?
- cell (tissue) cultures - used for eukaryotes
- bacteria cultures - used for bacteriophages
what are the units used to express concentration of infectious units?
- plaque-forming units (PFU)
- PFU/ml = number of plaquest/sample dilution
do prion disease have a treatment?
what must be present fro neural degeneration to occur?
PrPc prion must be present for neural degeneration to occur
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