Viruses Acellular Pathogens Flashcards
Define Virus
genetic element that cannot replicate independently of a living ( host) cell
Define virology
study of viruses
Define virus particle
- extracellular form of virus
- facilitates transmission from 1 host to another
Define virion
infectious virus particles
What are 5 general characteristics of viruses
- Obligatory intracellular parasites ( require living host cells to multiply)
- contain DNA or RNA
- contain a protein coat
- no ribosomes so no protein synthesis
- no ATP generating mechanism so no metabolism
What 2 factors determine the spectrum of a host xells a virus can infect
Determined by specific host attachment sites and cellular factors
Can ppl be immuned to viruses
yes, if they don’t have receptors for the virus on therei cells
What are the classifications based on host
Bacterial viruses
Animal viruses
Plant viruses
What are 5 viral structures
1) nucleic acid
2) capsid
3) nucleocapsid
4) envelope
5) spikes
Describe viral nucleic acid
1) DNA OR RNA
2) single stranded or double stranded
3) linear or circular
What is the capsid made of
protein coat made of capsomeres ( subunits)
Define nuceocapsid
complex of nucleic acid and capsid
What is the envelope made of
lipid, protein, and carbohydrates coating on some viruses
classified as enveloped virus or non envelope virus
Define spikes
projections from outer surface
has surface proteins
What in the general morphology of viruses based on
on the bases of their capsid shapes
What are the 4 types of viruses
1) helical virus
2) polyhedral virus
3) enveloped viruses
4) complex viruses
What are helical viruses
1) shaped like long rods
2) the capsids are hollow cylinders that has helical structure
3) nucleic acid coiled
ex. rabies and ebola virus
What are polyhedral virus
viruses with capsids that are many sided
ex. poliovirus,adenovirus
‘plants,bacteria,anmal viruses has this shape
Define enveloped viruses
enveloped and spiked and capsomes
ex. influenza ( helical)
polyhedral ( herpes virus)
Define complex viruses
complicated structures
ex. bacteriophage
capsid head, sheath
Can we grow viruses in the lab
yes
viruses must be grown in living cells
bacteriophages form plaques on a lawn of bacteria
plaque forming unit ( PFU)
What are 3 ways of growing animal viruses in the lab
1) in living animals
2) in embryonate eggs
3) in cell cultures
Describe embryonated egg virus growth
virus injected into the egg
viral growth is signaled by changes or death of the embryo
ex. flu virus, vaccines
How are animal viruses grown in cell cultures
tissues treated with enzyme specific cells
infected cells detected detorioration-(cytopathic effect ( CPE))
continues cell lines are used
transformed cell grow in multiple layers
3 techniques for viral identification
1) cytopathetic effects
2) seroogical tests ( western blotting)
3) nucleic acids ( RFLPs or PCR)
2 requirements for viral multiplication
1) it must invade a host cell
2) it must take over the host’s metabolic machinary
What are the 3 periods in viral growth
Eclipse period
burst
decline
What happens in eclipse period
when it goes into host cell so unable to detect
What happens during burst phase
when comes out of host cell
What happens during decline in viral growth
when there is no more viable host cells will see a decline
What are 2 cycles of viral multiplication for bacteriophages
1) Lytic cycle
2) Lysogenic cycle
Define lytic cycle
phage causes lysis and death of the host cell
Define lysogenic cycle
phage DNA is incorporated in the host DNA
no cell death
What are 5 steps of multiplication of T-even bacteriophages (Lytic cycle)
1) Attachement: phage attaches to host cell
2) Penetration: phages penetrates host cell and injects its DNA
3) Biosynthesis: phage DNA directs synthesis of viral components by the host cell
4) maturation: viral components reassembled into virions
5) Release: Host cell lyses and new virions are released
What are 7 steps of multiplication of animal viruses
1) attachment
2) entry and uncoating.virions enter cell and its DNA is uncoated ( fusion or receptor-mediated endocytosis)
3) A portion of viral DNA is transcribed producing mRNA that encodes “early” viral proteins
4) biosynthesis. viral DNA is replicated and some viral proteins are made
5) late translation; capsid proteins are synthesized
6) Maturation virions mature
7) release virions are released via budding
What are 2 forms of attachment and penetration
1) endocytosis
2) fusion
Define endocytosis
entry of toga virus by pinocytosis
Define fusion
entry of herpes virus by fusion
capsid releases its DNA or RNA to work in cell
Describe of budding of an enveloped virus
host cell plasma membrane create envelope
What are 5 possible effects that animal viruses may have on cells
1) Transformation into tumor cell ( oncogene activation) TRANSFORMATION
2) Death of cell and release of virus LYSIS
3) Slow release of virus w/o cell death ( Persistent infection)
4) virus present but not replicating ( Latent infection)
5) cell fusion
Describe oncogenic DNA virus (2)
human papilloma virus ( HPV)- cervical cancer
Hepatitis B virus(HBV)- liver cancer
Describe oncogenic rna viruses
human t-cell leukemia virus (HTLV-1 and HTLV-2) -LEUKEMIA AND LYMPHOMA
Describe viroids
short pieces of naked RNA small,circular single stranded plant disease ( potatoe spindle fiber disease)
Define prions
proteinaceous infectious particles
How are prions inherited and transmissible
ingestion,transplant, and surgical instruments
What are 4 examples of prions
1) Mad-cow disease
2) Creutzfeldt-Jakob Disease (CJD)
3) fATAL familial insomia
4) sheep scrapie
Define PrPc
normal cellular prion protein, on the cell surface
Define PrPsc
scrapie protein’ accumulates in brain cell, forming plague
8 steps how a protein can be infectious
1) PrPc produced by cells is secreated to the cell surface
2) PrPsc may be acquired or produced by an altered PrPc gene
3) PrPsc reacts with PrPc on the cell structure
4) Pr Psc converts the PrPc to PrPsc
5) The new PrPsc converts more PrPc
6) the new PrPsc is taken in by endocytosis
7) PrPsc accumulates in endosomes
8) PrPsc cont. to accumulate as the endosome contents are transferred to lysosomes. The result is cell death
