bacterial genetics ch18 l.
Download
Skip this Video
Loading SlideShow in 5 Seconds..
Bacterial Genetics (Ch18) PowerPoint Presentation
Download Presentation
Bacterial Genetics (Ch18)

Loading in 2 Seconds...

play fullscreen
1 / 16

Bacterial Genetics (Ch18) - PowerPoint PPT Presentation


  • 170 Views
  • Uploaded on

Bacterial Genetics (Ch18). Genetic diversity caused by Rapid reproduction Mutation Recombination. Bacteria One of the simplest genetic model systems to study the mechanisms of molecular genetics Escherichia coli (E. coli) Intestinal flora “lab rat” of molecular biology.

loader
I am the owner, or an agent authorized to act on behalf of the owner, of the copyrighted work described.
capcha
Download Presentation

PowerPoint Slideshow about 'Bacterial Genetics (Ch18)' - xadrian


An Image/Link below is provided (as is) to download presentation

Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.


- - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - -
Presentation Transcript
bacterial genetics ch18
Bacterial Genetics (Ch18)

Genetic diversity caused by

Rapid reproduction

Mutation

Recombination

Bacteria

  • One of the simplest genetic model systems to study the mechanisms of molecular genetics

Escherichia coli(E. coli)

  • Intestinal flora
  • “lab rat” of molecular biology
replication of bacterial genome
Replication of bacterial genome
  • One circular DNA genome
    • Single origin of replication (Ori)
    • Bidirectional DNA replication
  • May have plasmids
    • smaller circular DNA molecules
      • Autonomously replicated (contain ori)
  • Bacteria divide by binary fission
  • asexual reproduction
  • Progeny are genetically identical to parent (clones)
le 18 14

Bacterial DNA

replication

Replication fork

LE 18-14

Origin of

replication

Both genome

& plasmid replicate

in this manner

Termination

of replication

bacterial dna mutation
Bacterial DNA Mutation

Caused spontaneously (mistakes in DNA synthesis)

  • Physicochemical forces (UV, X rays, chemical mutagens, etc.)
  • Since reproduction is quick e.g.doubling time=20 min
  • New mutations spread quickly
slide5

Calculation of incidence of mutations

If doubling time= 20 min, then 23cells/hr

Over 12 hr, 236 cells (~1010)produced from a single cell

If spontaneous mutation rate = 1 x 10-7 / gene,

then in 12 hr (day) (1010) (10-7)= 103 mutations/gene/day

If bacteria have ~4000 genes

then (4x103genes)(103)= 4 x 109 mutations/day

slide6

Take home message:

bacterial mutations rare per gene

But due to rapid cell division, become frequent

Major contribution to genetic diversity and

ability to adapt

another source of bacterial genetic diversity genetic recombination
Another source of bacterial genetic diversity:Genetic Recombination
  • Three processes bring bacterial DNA from different individuals together:
    • Transduction
    • Transformation
    • Conjugation
transduction
Transduction
  • Bacteriophages (bacterial viruses) transfer bacterial genes from one host cell to another
le 18 16

Phage DNA

A+

B+

LE 18-16

A+

B+

Donor

cell

A+

Crossing

over

A+

A-

B–

Recipient

cell

A+

B–

Recombinant cell

transformation
Transformation
  • Alteration of a bacterial cell’s genotype and phenotype
    • by the uptake of naked, foreign DNA from the surrounding environment
  • For example, harmless Streptococcus pneumoniae bacteria can be transformed to pneumonia-causing cells
  • Uptake of ampicillin resistant/ GFP-carrying plasmid (done in lab) (pGLO)
conjugation
Conjugation
  • Direct transfer of DNA between live bacterial cells that are temporarily joined
  • Transfer one-way:
    • “Male” donates DNA
    • “Female” receives DNA
slide12
“Maleness,”
    • Contains F (fertility) genes on plasmid or in genome
    • Encode sex pilus
      • Forms passage way for DNA from donor to recipient
le 18 17

LE 18-17

Sex pilus

5 µm

slide14
Donor cells containing the F plasmid: F+
  • Recipient cells: F-
  • Cells with F factor integrated into genome: Hfr cell

(high frequency of recombination)

  • Hfr cells
    • Transfer some genomic DNA to recipient cell
le 18 18 4

F plasmid

Bacterial chromosome

F+cell

F+ cell

Mating

bridge

LE 18-18_4

F– cell

F+ cell

Bacterial

chromosome

Conjugation and transfer of F plasmid from and F+ donor to an F– recipient

Formation of Hfr (high frequency of recombination) cell

Hfr cell

F+ cell

F factor

Hfr cell

F– cell

Temporary

partial

diploid

Recombinant F–

bacterium

Conjugation and transfer of part of the bacterial chromosome from an

Hfr donor to an F– recipient, resulting in recombiination