Viruses- Are they alive?

• Acellular• Can not metabolize• Can’t grow or respond to environment• Can’t reproduce without host

• Discovery- Wendell Stanley- tobacco mosaic virus

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

Enveloped virion

• Membrane acquired from its host cell during viral replication or release

• Composed of phospholipid bilayer & proteins- specific for host attachment

Bacteriophage

• Infects bacteria• Replication-

– 2 cycles

Lytic Cycle-pg 390(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- pg 392(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

Virus Life Cycle

• http://www.hhmi.org/biointeractive/hiv-life-cycle?utm_source=BioInteractive+News&utm_campaign=8559c11a70-BioInteractive_News_Vol_309_15_2014&utm_medium=email&utm_term=0_98b2f5c6ba-8559c11a70-69298381

Animations

• www.youtube.com/watch?v=wVkCyU5aeeU

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

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