viruses Flashcards
virus
non cellular infectious agent
characteristics of all viruses
1) protein coat wrapped around DNA or RNA (protein and nucleic acid)
2) cannot reproduce by itself (not a living thing)
3) rapid replication= rapid evolution
new phenotypes/protein coats
why are viruses not living things
not cells
cant reproduce
can have single stranded DNA and double stranded RNA
classification of viruses based on
type of protein coat (capsid)
nucleic acid type (RNA or DNA)
Envelope presence
size ranges for viruses
18nm-350nm
simple virus
- hollow protein shell
- protruding molecules that bind to host cell
tricks cell into taking it in through the glycoprotein
complex virus
more parts
1. head, neck, tail
2. bacteriophage
injects DNA into host
enveloped virus
capsid surrounded
by layer of membrane
glycoproteins attach to receptors and convince to let in. Mail themselves in host cell membrane so makes them hard to find
nucleic acids for virus
Double/single stranded DNA
Double/single stranded RNA
Largest segment containing 4 genes
RNA virus =
retrovirus
RNA can be
used as a template to make viral mRNA (use the host to make copies) or copied into DNA by reverse transcriptase (converts viral RNA -> DNA)
why do retroviruses mutate faster than DNA virus
because RNA polymerase and reverse transcriptase have no proofreading
enveloped viruses makeup and process
wrapped in a layer of host cell membrane
Intermembrane viral glycoproteins protruding out of membrane bind to host cell (tricks host)
Protovirus DNA integrates by integrase into host DNA
New viruses can leave host cell without lysis. (makes host cell make copies and then releases)
HIV=
enveloped retrovirus
HIV virus binds to
cellular receptors on white blood cells called T cells
T cells
immune cells so immune deficiency
HIV envelope retrovirus process
Protovirus integrates into T-cell DNA
We can not get to the protovirus in the nucleus so very difficult to treat
what is HIV positive but no AIDS
when the protovirus remains inactive in the T-Cells for years. Can be activated when immune system low
Viral Multiplication(component assembly model)
attachment, penetration,
replication and protein synthesis,
assembly,
release
attachment
virus chemically recognizes host and locks on
penetration
entire virus or virus DNA/RNA enters host cell
Replication & protein synthesis
of Viral genes makes viral proteins and DNA/RNA
assembly
new viruses put together into capsid
release
new viruses leave host cell either burst out through lysis or just leave through exocytosis
viral multiplication lytic pathway
steps proceed rapidly and end in lysing of the cell, bursting.
lysogenic pathway
Viral DNA integrated into host DNA
Viral DNA copied each time host cell divides
Latent period
Stimulus (depresses immune system) causes switch to lytic cycle and symptoms appear
can give new properties to host cells
latent period
= no symptoms but more and more host cells are becoming infected
example of lysogenic pathway
type 1 herpes simplex, cold sores
example of giving new properties to host cell in lysogenic pathways
cut into cell so can cut certain genes, results in Increased pathogenicity (worse symptoms) in bacteria
transduction
Bacterial genes transferred from one bacteria to another via virus particles
Viral proteins mutate rapidly due to
replication & transcription errors
rapid reproduction rates
obtaining genes from other viruses that occupy the same host cell – ex: bird flu and swine flu
why do we need new shots for viruses
mutate rapidly so need New shots to help immune system recognize the changed virus
prions
proteins in nervous system
infectious prions
Infectious prions are misfolded
Misfolded prions deposit in brain
Misfolded prions can cause normal prions to misfold
Infectious Prions not destroyed by cooking!
mad cow disease =
BSE
beef infected with BSE can cause
vCDJ in humans, cause human prions to misfold
where is mad cow found in
Brains and spinal tissue of a cow
