bacterial genetics & genetic engineering

bacterial chromosome

1 double-stranded circular DNA molecules + associated proteins

• plasmids: small circular pieces of DNA (exist & replicate independent of bacterial chromosome)

  • not required but give benefits

reproduction in bacteria

reproduce by binary fission (asexual) — produce genetic clones

• mutation = source of variation

mechanism of gene transfer/recombination in bacteria

1. transformation

2. conjugation

3. transduction

transformation

when small pieces of DNA are taken up by the bacterium from its surrounding environment

• can be from free DNA piece or plasmid

  • free can be incorperated into bacterial chromosome

  • plasmid can operate independently or incorporated

biotech link with transformation

genes of interest are splice using restriction enzymes & the bacterial cells can me “made” to take up the plasmid (competency)

how to make bacterial cells competent

1. heat shock: quickly change temp of bacteria’s environment

2. altering calcium ion concentration

3. electrical impulses

conjugated (bacterial sex)

unidirectional transfer of genetic material between 2 bacterial cells

• male has pili (protein-hair like extensions) that attach to female

  • they join & DNA is passed from male to female

what determines bacteria’s ability to form pili

f-factor (fertility factor) — codes for production of sex pili — can be found on bacterial chromosome or plasmid (f plasmid)

biotechnology link with conjugation

specific plasmid is r plasmid (antibiotic resistance)

• antibiotics disrupt bacterial cells wall & kill bacteria

• gene mutations have led to production of functional proteins that result in antibiotic resistance

  • r plasmids carry f-factor — can pass it on

how to gene mutations negate the effects of antibiotics

1. blocking uptake of antibiotic into the bacterium

2. enzymatically breaking down the antibiotic before it is taken up

transduction

bacterial DNA is transferred from one bacterium to another on the back of bacteriophage particles

how does the mechanism for transduction work

during lytic cycle of bacteriophage virus the bacterial DNA is degreades & small piece is packaged into capsid as new bacteriophage is assembled

• makes it useless

• the bit of DNA can now be incorporated into new bacterial host & genes can be expressed

genetic engineering

recombining DNA from two different sources for commercial use

dna cloning