Download Bacteria

Bacteria
* Adaptable
* Evolutionarily and environmentally
* Bacterial chromosome
* Double stranded DNA
* Circular
* E. coli- 4,300 genes
* No nucleus, chromosome is found in dense area, nucleoid
* May also have xtra DNA in smaller circles, plasmids.
* Division- DNA copies itself in both directions until entire
circle has been replicated.
- Then divides by binary fission.
* Divide very quickly under good conditions.
* E. coli divides every 20 minutes
* 2 x 1010 new bacteria per day in a human colon
* A colony of bacteria are genetically identical to each other
* But, of 2 x 1010 produced, approximately 2000 will have a
mutation in regard to one gene.
* Remember, 4300 genes, so approx. 9 million bacterial
genes will mutate per day per human host.
* More diversity, those more equipped to survive will be
more successful.
Genetic Recombination
* 2 strains of E. coli
1) Cannot produce essential amino acid, tryptophan (trp-)
2) Cannot produce essential amino acid, arginine (arg-)
* Place both strains in a petri dish containing only glucose
(food).
* 24 hours later, colonies appear.
* How??
* Genetic info. from 2 strains has combined to produce a
new strain that produces both arg & trp.
* Not from fertilization (like eukaryotes)
* So...
1) Transformation- Alteration of a chromosome by uptake
of foreign DNA from the surrounding environment.
2) Transduction
a) Generalized- Phage infects bacterium. When new
viral particles form, some accidentally take up some
bacterial DNA pieces.
* When that phage leaves, it infects another
bacterial cell & gives it this piece of DNA
* Recombination occurs
b) Specialized- Requires a temperate phage
* Phage integrates into bacterial genome
* Later, when it gets cut out, some of the bacterial
DNA gets cut out, too.
* This DNA goes with the phage DNA to a new host
cell later on & recombines into that bacterial
genome
3) Conjugation- Direct transfer of DNA from one
bacterial cell to another.
* One cell attaches to another by a pilus & retracts,
pulling the 2 together.
* A cytoplasmic bridge forms from one cell (“male”) to
the other (“female”).
* “Male” cell has a piece of DNA to code for
production of pilus, called F factor.
* Found in chromosome or plasmid
Plasmids & Conjugation
* Genes not necessary for daily survival of a bacterium
* Genes are necessary for survival in stressful
environments.
* If a cell has an F factor on a plasmid (“male”), it is called
F+. No factor (“female”), F* When conjugation occurs, F+ cell passes F plasmid to Fcell so it becomes F+ also.
* If F factor is on chromosome (not on plasmid), it is called
an Hfr cell (high frequency of recombination).
* When conjugation occurs, since F factor is on
chromosome, the chromosome gets passed to “female”
cell.
R Plasmids & Antibiotic Resistance
* Some bacteria gain resistance to antibiotics over time
* Certain genes code for enzymes that destroy antibiotics
* These genes are found on R plasmids.
Transposons- “Jumping Genes” (Fig. 18.17)
* Piece of DNA that can move from one area of the
chromosome to another