1. The Genetics of Bacteria: Bacterial Reproduction
Ms. Gaynor
The Genetics of Bacteria: Bacterial Reproduction

2. Did you know..?
human gut holds about 1,000 different bacterial species & some 10 trillion bacterial cells  

3. What is Bacteria? Single celled prokaryote
No nucleus (nucleoid region instead)
Very few (“no”) organelles
Has a cell wall, cell membrane, ribosomes, cytoplasm
Has circular chromosome and plasmid(s)

4. Prokaryote vs. Eukaryote
It is important to note that most bacteria do not have histones, and yet they do have SIR2-like proteins with similar activity

6. 2 Types (domains) of Bacteria
Eubacteria (can be harmful)
“regular” bacteria
They live in most environments
their cell-wall DOES contain peptidoglycan
Archaea Bacteria (not harmful)
“older” bacteria; live in EXTREME habitats
more similar to eukaryotes than to bacteria in several ways:
their cell-wall does NOT contain peptidoglycan

7. Antibiotics kill these type!
Eubacteria Cell Wall
Antibiotics kill these type!

8. 3 Bacterial Shapes

9. Genetic Diversity of Bacteria
Rapid reproduction, mutation, and genetic recombination contribute to the genetic diversity of bacteria
The well-studied intestinal bacterium Escherichia coli (E. coli) is “the laboratory rat of molecular biology”

10. Bacterial Genetics
Nucleoid region  densely packed with DNA (no membrane)
The bacterial chromosome
usually a circular DNA molecule with few associated proteins
Reproduction binary fission (asexual)

11. Mutation and Genetic Recombination as Sources of Genetic Variation
Since bacteria can reproduce rapidly
New mutations can quickly increase a population’s genetic diversity
Genetic diversity
Can also arise by genetic recombination of the DNA from 2 different bacterial cells
***Remember that prokaryotes don’t undergo meiosis (crossing over) or fertilization

12. Plasmids
In addition to the chromosome, some bacteria (and plants) have plasmids
smaller circular DNA molecules that can replicate independently of the bacterial chromosome
Extra chromosomal DNA
Does not code for genes that aid in cell replication
Do not transcribe/translate their DNA into protein

13. Since asexual reproduction is used, how does Bacteria Transfer DNA?
Conjugation
direct transfer of genetic material; forms cytoplasmic bridges; sex pili used
Transduction
phages that carry bacterial genes from 1 host cell to another
generalized~ random transfer from host #1 to host #2
specialized~ incorporation of prophage DNA into host chromosome
Transformation
gene alteration by the uptake of naked, foreign DNA (plasmid) from the environment

14. #1) Conjugation Conjugation
the direct transfer of genetic material between bacterial cells that are temporarily joined
Sex pili are used in the transfer of DNA

15. LE 18-17
Sex pilus
5 µm

16. Bacterial Plasmids
Small, circular, self-replicating DNA separate from the bacterial chromosome
F (fertility) Plasmid: codes for the production of sex pili (bacteria are either F+ or F-)
R (resistance) Plasmid: codes for antibiotic drug resistance
Transposons (transposable genetic elements): piece of DNA that can move from location to another in a cell’s genome
chromosome to plasmid, plasmid to plasmid, etc.
They are commonly referred to as “jumping genes”

17. Conjunction and transfer of an F plasmid
From and F+ donor to an F– recipient
F plasmid
Bacterial chromosome
F+ cell
F+ cell
Mating
bridge
F– cell
F+ cell
Bacterial
chromosome

18. R plasmids and Antibiotic Resistance
R plasmids resist various antibiotics
When a bacterial population is exposed to an antibiotic, individuals with the R plasmid will survive and increase in the overall population

19. Conjugation Animations of F Plasmid
Conjugation Animations of R Plasmid
Rolling Circle Plasmid Transfer Mechanisms Animations

20. #2) Transduction Transduction
Phages (viruses) that carry bacterial genes from 1 host cell to another
generalized~ random transfer from host #1 to host #2
specialized~ incorporation of prophage DNA into host chromosome

21. Specialized Transduction Animations
Generalized Transduction Animations
Specialized Transduction Animations

22. #3) Transformation Transformation
“Naked” Plasmids (present in environment) are taken up by certain bacteria
Viruses are NOT used in this method!

23. Bacterial Transformation Animations

24. Transposon Animations

25. The Genetics of Bacteria: Operons
Ms. Gaynor
Chapter 18 (PART 3)
The Genetics of Bacteria: Operons

26. REVIEW How do bacteria exchange DNA or acquire NEW genes?
Transformation
Trandsduction (both generalized and specialized)
Conjugation
Insertion sequences and Transposons

27. Used by bacteria for gene regulation
OPERONS
Used by bacteria for gene regulation

28. How do Bacteria Control Gene Expression?
Individual bacteria respond to environmental change by regulating their gene expression
A bacterium can ADJUST its metabolism to the changing environment and food sources
This metabolic control occurs on 2 levels:
Adjusting activity of enzymes
Regulating genes that encode enzymes

29. Regulation of enzyme activity Regulation of enzyme production
LE 18-20
Regulation of enzyme
activity
Regulation of enzyme
production
Precursor
Feedback
inhibition
Enzyme 1
Gene 1
Enzyme 2
Gene 2
Regulation
of gene
expression
Enzyme 3
Gene 3
Enzyme 4
Gene 4
Enzyme 5
Gene 5
Tryptophan

30. Operons: The Basic Concept
Mostly in bacteria  genes are often clustered (grouped) into operons
INCLUDES:
An operator, an “on-off” switch
A promoter with a TATA box
Genes for metabolic enzymes
An operon can be switched off by a protein called a repressor
A corepressor is a small molecule that cooperates with a repressor to switch operon off

31. Operon Parts The regulatory gene codes for the repressor protein.
The promoter site is the attachment site for RNA polymerase (proceeded by TATA box)
The operator site is the attachment site for the repressor protein.
The structural genes code for the proteins.
The repressor protein is different for each operon and is custom fit to the regulatory metabolite.
Whether or not the repressor protein can bind to the operator site is determined by the type of operon.
The regulatory metabolite is either the product of the reaction or the reactant depending on the type of operon.
What is a regulatory protein?

32. Operon- Example #1 trp operon- a repressible operon
Used to MAKE tryptophan (amino acid)
Promoter (and TATA box): RNA polymerase binding site; begins transcription
operator: controls access of RNA polymerase to genes (EMPTY when tryptophan NOT present)
repressor: protein that binds to operator and prevents attachment of RNA polymerase
coded from a regulatory gene (when tryptophan is present ~ acts as a corepressor)
transcription is repressed when tryptophan binds to a regulatory protein

33. NO Tryptophan present repressor
Inactive  operon ON
DNA
Regulatory
gene
mRNA
Protein
TATA Box and Promoter
trpR
RNA
polymerase 3¢ 5¢
Inactive
repressor
mRNA 5¢
trpE
trpD
trpC
trpB
trpA
Operator
Start codon
Stop codon
trp operon
Structural Genes of operon E
Polypeptides that make up
Enzymes needed to make tryptophan D C B A

34. Tryptophan present  repressor
LE 18-21b_1
DNA
mRNA
Protein
Active
repressor
Tryptophan
(corepressor)
Tryptophan present  repressor
active  operon OFF

35. Tryptophan present, repressor active, operon off
LE 18-21b_2
DNA
No RNA made
mRNA
Protein
Active
repressor
Tryptophan
(corepressor)
Tryptophan present, repressor active, operon off

36. Tryptophan Repressor Operon
Animation #1

37. Operon- Example #2 lac operon- an inducible operon
lactose metabolism (assume NO glucose in habitat)
When lactose not present:
repressor active
operon off
no transcription for lactose enzymes
When lactose present:
repressor inactive
operon on
inducer molecule inactivates protein repressor (allolactose)
transcription is stimulated when inducer binds to a regulatory protein

38. Recall…What are Glucose and Lactose?
Monosaccharide
Needed for bacterial glycolysis and proton gradient formation…why?
To make their ATP (remember no cellular respiration b/c NO mitochondria)
Lactose
Disaccharide
made of glucose and galactose

39. How do bacteria make ATP?
Glucose is needed!
Needed for bacterial glycolysis to make 2 ATP via substrate level phosphorylation (just like eukaryotes)
Electrons from glucose needed to create H+ gradient so ATP synathase can function
…WAIT!!! Bacteria have NO mitochondria cristae so where does this proton gradient/ATP synthase complex take place
IT THE CELL MEMBRANE OF THE BACTERIAL CELL!!!

40. Lactose absent  repressor
LE 18-22a
Regulatory
gene
Promoter
Operator
DNA
lacl
lacZ No
RNA
made 3¢
mRNA
RNA
polymerase 5¢
Active
repressor
Protein
Lactose absent  repressor
active  operon OFF

41. Lactose present  repressor
LE 18-22b
lac operon
DNA
lacl
lacZ
lacY
lacA
RNA
polymerase 3¢
mRNA
mRNA 5¢ 5¢
Permease
Transacetylase
Protein
-Galactosidase
Enzymes needed for lactose metabolism
Inactive
repressor
Allolactose
(inducer)
Lactose present  repressor
inactive  operon ON

42. Repressible and Inducible Operons: 2 Types of Negative Gene Regulation
A repressible operon is usually on
binding of a repressor to operator shuts off transcription
The trp operon is a repressible operon
An inducible operon is usually off
a molecule called an inducer inactivates the repressor and turns on transcription
Example of an inducible operon is the lac operon, which contains genes coding for enzymes in hydrolysis and metabolism of lactose

43. Inducible enzymes usually function in catabolic pathways
Repressible enzymes usually function in anabolic pathways
Regulation of the trp and lac operons involves negative control of genes because operons are switched off by the active form of the repressor

44. Positive Gene Regulation
Some operons are also subject to positive control through a stimulatory activator protein, such as catabolite activator protein (CAP)
When glucose (a preferred food source of E. coli ) is scarce, the lac operon is activated by the binding of CAP
When glucose levels increase, CAP detaches from the lac operon, turning it off

45. REVIEW OF ATP
ATP vs. ADP
Low levels of glucose (AMP/cAMP)

46. Lactose present, glucose scarce (cAMP level high): abundant lac mRNA
LE 18-23a
Promoter
DNA
lacl
lacZ
RNA
polymerase
can bind
and transcribe
CAP-binding site
Operator
Active
CAP
cAMP
Inactive lac
repressor
Inactive
CAP
Lactose present, glucose scarce
(cAMP level high): abundant lac mRNA
synthesized

47. Lactose present, glucose present (cAMP level low): little lac mRNA
Promoter
DNA
lacl
lacZ
CAP-binding site
Operator
RNA
polymerase
can’t bind
Inactive
CAP
Inactive lac
repressor
Lactose present, glucose present
(cAMP level low): little lac mRNA
synthesized

48. Lac Operon (with and without lactose/ glucose)