Transcript Viruses - North Mac Schools

No
19-3 Viruses
Are they alive?
Yes
• Acellular
• Have DNA or RNA
• Can not metabolize
• Evolve
• Can’t grow or respond
to environment
• Can’t reproduce
without host- obligate
parasites
• *can only be seen
with electron
microscope
Virion- virus outside of cell
• Capsid-protein coat surrounding nucleic acid
• Genetic material- DNA or RNA
–
–
–
–
dsDNA- double stranded DNA
ssDNA- single stranded DNA
dsRNA- double stranded RNA
ssRNA- single stranded RNA
• Super small amount of genes
• Capsomeres- Surface proteins- only attach to
particular host or even specific cells in the host
Discovery- they were looking for
the cause of Tobacco Mosaic Virus
• 1883- Adolf Mayer-disease is contagious
• 1892- Dmitri Ivanovsky- uses filter to trap
“bacteria”
• 1897-Martinus Beijerinch- caused by
something smaller than bacteria
• 1898-named virus- meaning “poison”
• 1935- Wendell Stanley- isolates virus
Bacteriophage
• Infects bacteria
• Replication– 2 cycles
Enveloped virion
• Membrane acquired from its host cell
during viral replication or release
• Composed of phospholipid bilayer &
proteins- specific for host attachment
Lytic Cycle
(virulent-causes disease)
1. Attachment - the virus attaches itself to the host cell.
2. Injection - the virus inserts its genetic material into the
host cell.
3. Integration & Replication- the genetic material tells the
cell what to do & the host cell builds parts of the virus.
4. Assembly - the cell assembles the replicated parts into
new viruses.
5. Lysis - the cell breaks open and each replicated virus
can now infect other cells.
Lysogenic Cycle
(temperate- doesn’t kill right away)
1. Attachment
2. Injection
3. Integration- virus DNA becomes part of
bacterial DNA- prophage
4. Replication- when host cell replicates its own
DNA, virus DNA is also copied
5. Assembly
6. Trigger > Lytic Cycle
•
can be caused by sunlight, radiation, chemicals
Lytic vs Lysogenic Cycles
• www.youtube.com/watch?v=wVkCyU5aee
U
• http://www.youtube.com/watch?v=_J9xKitsd0&feature=related
How do Animal viruses replicate?
• Same steps as bacteriophages, just some
differences in what is happening in each
– Ex: removal of outer coat
Latency
• -viruses remain dormant in cells
• Prolonged viral activity for years
– Ex: chickenpox, herpes
• Can become integrated into host’s
chromosomal information permanently, so
all cells after that are infected
– Ex: HIV
Viroids
• Small, circular pieces of RNA that are
infectious to plants
• Lack capsids
• May appear linear
Prions
• Not viruses because they lack nucleic acid
• Composed of single protein- PrP
– All mammals contain a gene that codes for
the a.a. sequence for cellular PrP
• Can re-fold into stable structures,
changing shape & become harmful
• Excess PrP or mutations cause the prion
PrP
• 40% of humans have PrP that can misfold
Retroviruses
• Work “backwards”
– RNA > DNA > RNA > Protein
– HIV
– http://www.youtube.com/watch?v=eS1GODin
O8w
Treeman
• http://www.hlntv.com/video/2013/10/03/tre
e-man-genetic-condition-growths-handslegs
Vaccines
• How are they made?
– Reading
– http://content.time.com/time/video/player/0,32
068,60312463001_1951560,00.html