T4 bacteriophage infecting an E. coli cell

1
T4 bacteriophage infecting an E. coli cell
2
Comparing the size of a virus, a bacterium, and
an animal cell
3
Basic shapes of bacteria

• Bacillus ? rod-like
• Coccus ? round
• Spirillium ? spiral

4
Roles of non-pathogenic bacteria

• Some examples
• Decomposition
• Intestinal mutualistic relationship
• Food prep

5
Genetics of Bacteria

• Bacterial genome ?

6
Genetics of Bacteria

• Bacterial genome ? One circular DNA molecule
• E. coli chromosome has 100 times more DNA than in
  a typical virus, but much less than a eukaryotic
  cell.
• Packed into nucleoid region of cell
• Plasmid ?

7
Genetics of Bacteria

• Bacterial genome ? One circular DNA molecule
• E. coli chromosome has 100 times more DNA than in
  a typical virus, but much less than a eukaryotic
  cell.
• Packed into nucleoid region of cell
• Plasmid ? small circular extra piece of DNA

8
Bacterial Genetic Recombination

• What is the main source of genetic recombination
  in bacteria?
• Mutations
• What are the other sources of recombination?
• Transformation
• Transduction
• Conjugation

9
General steps to transformation

• Isolate gene of interest using restriction
  enzymes
• Expose recipient bacterium to same restriction
  enzyme, temperature shock, ions, and DNA binding
  protein
• Combine gene of interest with recipient bacterium

10
Transformation ? uptake of naked, foreign DNA
11
(No Transcript)
12
Transduction bacterial genes moved from one host
to another
What is the vector of transduction? A phage
13
(No Transcript)
14
 Bacterial conjugation
15
Conjugation

• Defined as the direct transfer of genetic
  material between 2 bacterial cells that are
  temporarily joined
• male bacterium uses a sex pilus to pull
  female bacterium towards it creating a mating
  bridgeserves as the avenue for DNA transfer
• There needs to be a fertility (F) gene present
  either as part of the bacterial genome or as a
  plasmidan F plasmid is an episome
• ? genetic element that can replicate
  independently or as part of the bacterial genome

16
Conjugation
17
(No Transcript)
18

• Plasmid genes are advantageous to the bacteria
  that have them
• Plasmids that confer resistance to antibiotics
  are called R plasmids

19
Transposons

• Jumping genes (do not exist independentlyeither
  a part of a plasmid or the bacterial chromosome)
• Does not depend on complementary base pairing
  between homologous regions of the chromosome.
• Transposons move to regions that the gene has
  never been (ex. plasmid ? chromosome)

20
Transposase recognizes the inverted repeats
21
Targeted inverted repeats are cut, and the target
is cut, then the transposon is inserted
22
Composite transposons move extra genes along with
the inserted sequence, and are very beneficial to
the bacteria
23
Operons

• Regulatory systems in E.coli
• 2 Types Repressible or Inducible
• 5 components
• Regulatory gene (codes for mRNA to be translated
  into repressor protein)
• Promoter (site on gene where RNA pol. binds to
  begin transcription)
• Operator (on/off switch)
• Repressor (binds to the operator to turn operon
  gene off)
• Corepressor (allosterically binds to repressor to
  change shape of repressor to turn the operon gene
  off)
• OR
• Inducer (allosterically binds to the repressor to
  change the shape of the repressor to turn the
  gene on)

24
Regulation of Gene Expression
Structural Genes
25
Repressible operons

• Repressible operons have structural genes that
  code for the production of the substrate.
  (anabolic pathways)
• The repressor protein is produced in an inactive
  form, leaving the operator open and the genes on
• In the presence of the substrate, the substrate
  will allosterically bind to the repressor protein
  (is a co-repressor) and activate the repressor
  protein causing it to bind to the operator to
  turn the genes off

26
(No Transcript)
27
(No Transcript)
28
Inducible operons

• Inducible operons have structural genes that
  produce enzymes that break down the substrate.
  (catabolic pathways)
• The repressor is translated into its active
  configuration and will bind to the operator in
  the absence of the substrate to keep the gene
  off.
• If the substrate is present, it binds to the
  repressor protein and de-activates it, thereby
  opening up the operator and turning the gene on.

29
(No Transcript)
30
(No Transcript)
31
Glucose and its affects on the lac operon

• E.coli would prefer to use glucose as its fuel
• If glucose is scarce, cyclic AMP is abundant and
  serves as an allosteric activator to a regulatory
  protein called CAP ? stimulates RNA pol and
  transcription of enzymes that metabolize lactose
• If glucose is availabe, cyclic AMP (cAMP) is
  absent ? CAP detaches and transcription of the
  enzymes to metabolize lactose occurs at a very
  low level
• Lac repressor molecule turns operon genes on or
  off, CAP controls the rate of transcription

32
(No Transcript)
33
(No Transcript)
34
(No Transcript)
35
(No Transcript)
36
(No Transcript)
37
(No Transcript)