19-3 VirusesAre they alive?

• Acellular• Can not metabolize• Can’t grow or respond

to environment• Can’t reproduce

without host- obligate parasites

• Have DNA or RNA• Evolve

• *can only be seen with electron microscope

YesNo

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. Attachment2. Injection3. Integration- virus DNA becomes part of

bacterial DNA- prophage4. Replication- when host cell replicates its own

DNA, virus DNA is also copied5. Assembly6. Trigger > Lytic Cycle

• can be caused by sunlight, radiation, chemicals

Lytic vs Lysogenic Cycles

• www.youtube.com/watch?v=wVkCyU5aeeU

• http://www.youtube.com/watch?v=_J9-xKitsd0&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=eS1GODinO8w

Treeman

• http://www.hlntv.com/video/2013/10/03/tree-man-genetic-condition-growths-hands-legs

Vaccines

• How are they made?– Reading

– http://content.time.com/time/video/player/0,32068,60312463001_1951560,00.html