CHAPTER 18Microbial

Models: The Genetics of Viruses and

Bacteria

SizeAveragesEukaryotic

10 um.Bacteria 1 um.Viruses .1um.

Respiratory infections & pink eye

The human Papilloma virus causes warts and cervical cancer double stranded circular DNA

Adenovirus causes respiratory infections and pink eye

Bacteriophages

Simplified viral reproductive cycle

double stranded DNA

Lytic cycle of a T4 phage

Parts self-assemble

The lysogenic and lytic reproductive cycles of phage lambda a temperate phage

The reproductive cycle of an enveloped virus with a

single stranded RNA genome but not a

retrovirus

Structure and Life Cycle of an

HIV virusa retrovirus

HIV infection

Ebola virus-too virulent?

Deer mouse

Hanta virus

Vaccines- ”harmless” variations of the virus that initiate the immune system to form memory T-cells and B-cells

Synthetic vaccines-made from other viruses usually the smallpox virus with recombinant DNA technology, no possible infection

Tobacco mosaic virus

Tobacco mosaic virus

ViroidsTiny molecules of naked circular RNA. They do not

encode proteins but they can replicate in host cells using the hosts cells enzymes. They seem to only affect plants. Some how they disrupt metabolism of the plants and cause errors in regulation of protein synthesis. Affects tomatoes, potatoes, and palm trees

PrionsInfectious protein molecules that can somehow replicate in cells. They cause degenerative brain diseases. They cause scrapie in sheep, “mad cow disease” or bovine spongiform encephalitis, and Creutzfeldt Jacob disease in humans. Cause the normal form of a protein to fold up wrong and thus become a prion.

RESTRICTION ENZYMESRESTRICTION ENDONUCLEASES

Produced by bacteria for protection from viruses, they cut DNA at specific recognition sites and prevent it from taking over the cell. They can all be called endonucleases. They often make uneven cuts that leave short single-stranded pieces on each end called “sticky ends”

How do bacteria keep their own DNA from being cutby their restriction enzymes? Methylate their restriction sites

How are restriction enzymes used in recombinant DNA

technology?

Normal without an F+ episome

Replication of the bacterial chromosome begins at one origin and continues in both directions

Detecting genetic recombination in bacteriaSo, what happened?

Conjugation and recombination in E. coli

Plasmids-small rings of DNA that contain 2 - 30 genes and can replicate on their own when in a cell by rolling circle replication R plasmids contain genes for antibiotic resistanceHow could several genes for antibiotic resistance end up on the same plasmid?Transposons

Conjugation and recombination in E. coli

Conjugation and recombination in E. coli

F-pili

Insertion of a transposon

and creation of direct repeats

Anatomy of a composite transposon

The trp operon a Repressible OperonTryptophan absent, repressor inactive, operon on

The trp operon a Repressible OperonTryptophan present, repressor active

The trp operon a Repressible OperonTryptophan present, repressor active, operon off

The lac opreron: an inducible operon for enzymes that are only needed occasionally

What would happen if a mutation to the regulator gene produced a defective repressor protein?What would happen to the levels of the mRNA and the enzymes after all available lactose was digested?

Smallpox

Measles

Measles

Polio

Hepatitus

Killed 300,000 worldwideBegan in 1918

Herpes

E. coli DNA

plasmids