What is an operon?
Under control of promoter or repressor DNA sequence
Can activate or turn off expression of a gene or group of genes
Ex: lac operon
What is quorum sensing? What are examples of this?
Quorum sensing–virulence factors are only turned on when there are enough bacteria present–I need my friends around me before we do this thing!
Ex: Biofilm production by Pseudomonas sp
virulence factors of Staphylococcus aureus
Salmonella produces pathogeneticity islands. What are these?
a part of a genome that has its origin in horizontal transfer
they code for virulence & toxin factors
Hemolysin production by ________. What is this?
they are lysins that cause destruction of RBC membranes.
What is the function of the lac operon? What form of regulation does it show?
fcn: degradation of lactose–involves 3 enzymes whose genes are located next to each other
Negative Regulation–genes are turned off as default.
What are the 3 control genes?
Promoter in region of DNA where RNA polymerase initiates transcription
Operon - acts as traffic light for transcription of structural genes
Regulatory gene – codes for repressor protein
What happens to the lac operon in the absence of lactose?
operon is repressed by binding of repressor protein to the operator sequence
so the RNA polymerase can’t transcribe anything!
What happens to the lac operon in the presence of lactose?
lactose binds to the repressor protein & reverses the repression
RNA pol is allowed to transcribe the operon mRNA to make the enzymes to degrade lactose
Describe the structure of the lac operon.
Regulatory Gene–Promoter–Operator–Structural Genes
What are 3 enzymes that are translated from lac operon mRNA?
What are the 2 types of single base mutations?
Silent mutation – no change in encoded amino acid
Missense mutation – change in amino acid
What are 2 mutations that involves multiple bases?
**Deletion or insertion not in multiples of three, e.g., single base deletion
**Useless peptide or premature truncation
**Extensive insertion, deletion or gross rearrangement
**Destroys gene function
**May occur by recombination or genetic engineering
T/F Mutation of single bases or multiple bases is an efficient mechanism for bacteria to develop resistance to various antibiotics.
What is transformation?
uptake of naked DNA
What is conjugation?
One-way direct cell-to-cell transfer of DNA
Through the sex pilus
Common means for transfer of antibiotic resistance between species
What is transduction? What are the 2 types?
Transfer via bacterial viruses
Usually between the same or closely related species
2 types: General & specialized
What is generalized transduction?
Generalized – random due to accidental packaging of host DNA into phage
What is specialized transduction?
Specialized – genes adjacent to sites for integration of phage DNA into bacterial genome
Why was strep pneumoniae studied in the Griffin experiment?
this is encapsulated bacteria–allows it to survive in bloodstream, creates sepsis in the mouse.
inhibits phagocytosis & the pathogen is extracellular.
causes pneumonia in humans
**this bacteria was studied in the experiment.
In the Griffin experiment, what happened when live encapsulated strep pneumonia was injected into the mouse? What was extracted from the mouse?
- *the mouse died
* *colonies of encapsulated bacteria were isolated from the dead mouse
In the Griffin experiment, what happened when live non encapsulated strep pneumonia was injected into the mouse? What was extracted from the mouse?
- *the mouse lived
* *a few colonies were extracted; phagocytes destroyed non encapsulated bacteria
In the Griffin experiment, what happened when heat killed encapsulated strep pneumonia were injected into the mouse? What was extracted from the mouse?
- *mouse remained healthy
* *no colonies isolated from the mouse
In the Griffin experiment, what happened when live non encapsulated & heat killed encapsulated bacteria were injected into the mouse? What was extracted from the mouse? Why is this?
**colonies of encapsulated bacteria were isolated from the mouse
this happened b/c of transformation–the uptake of naked DNA
**basically: heating the encapsulated strep released its DNA. The non encapsulated guys took up the naked DNA (transformation) & became the full on encapsulated alive strep pneumonia. Kill the mouse!
What is transformation? What does it require?
transformation is the uptake of naked DNA
requires a competent cell–competent at the end of the log growth cycle
DNA integrated into the cell by homologous recombination
Which experiment was the first demonstration that DNA carries genetic information?
Avery, MacLeod and McCarty, 1946
How can transformation be encouraged by artificial means?
electroporation or inducing changes in membrane permeability
What is conjugation? What does it require?
one way transfer of DNA from a donor (male) cell to a recipient (female) though a sex pilus
Requires direct cell contact
Requires a special fertility factor (F factor) in the donor cell
The special fertility factor (F factor) is found in which form?
maintained as a plasmid
What is a plasmid?
small genetic elements that can replicate independently of the bacterial chromosome
What is an episome?
a plasmid that can integrate into the host chromosome
In terms of conjugation…what makes a bacteria male or female?
the presence or absence of the F factor.
F factor present: male
Describe the role of the F factor in conjugation.
Carries all genes necessary for its own transfer
Ability to make sex pilus
Ability to initiate DNA synthesis at the transfer origin of the plasmid
F plasmid transfers itself, making the recipient F+
What is the F pilus composed of?
repeating units of a single protein-F pilin.
What is the role of the F pilus in conjugation?
Binds to recipient (F-) cell and brings pair in close proximity–then able to exchange genetic material
What are Hfr cells?
this stands for high frequency of recombination
these are cells that have taken in the F plasmid to their chromosome.
How are genes transferred to other cells via conjugation once you have an Hfr cell?
you could theoretically just transfer a strand of the F plasmid that is integrated into the bacterial chromosome.
OR you can transfer the F plasmid w/ a bit of bacterial chromosome…this is the transfer of an F’ plasmid.
When you are transferring genes from an Hfr cell…which go first–bacterial genes next to F factor or F factor?
Genes adjacent to F factor go across first; F factor goes last
How does the bacterial chromosome integrate the F plasmid?
via reciprocal recombination–homologous recombination
What is oriT?
Site-specific cleavage at the replication origin for conjugal transfer
How does conjugation relate to mapping genes?
when you are transferring an integrated F plasmid…get some of the bacterial chromosome. When you interrupt the transfer–can sorta map the genes.
What types of info do plasmids carry?
What types of resistance do plasmids carry?
Genes for resistance to essentially all antibiotics
Resistance to many antibacterial compounds including heavy metals, mercurials, and toxic anions
Resistance to radiation
Resistance to some bacteriophage
What types of virulence factors do plasmids carry?
Bacteriocins – compounds toxic for other bacteria
Virulence factors – toxins, attachment proteins
T/F Plasmids are involved in various metabolic pathways.
What are transposons?
mobile genetic elements aka jumping genes
transfer DNA within a cell (as opposed to b/w cells)
from one position in the genome to another in the genome OR to a plasmid in the cell or something.
What are simple transposons? What are they also known as?
aka insertion sequences (IS)
these include inverted repeats for cutting & pasting without error
have code for transposase
T/F Transposon reintegration into the genome requires extensive homology.
False. Unlike homologous recombination, does not require regions of extensive homology for insertion
What are complex transposons?
these include insertion sequences
carry additional genes too–like a gene for antibiotic resistance or something
What’s the deal with conjugal resistance plasmids?
they carry RTF (resistance transfer factor) & r-determinant (drug resistance transposons)
What is the mechanism for multiple drug resistance?
& it is transferred to another bacterium via RTF
What does RTF encode?
it encodes the genes for conjugal transfer
T/F Complex transposons lack the transposase gene.
False. They have it.
What is transduction? What are the 2 types?
genetic transfer mediated by bacterial viruses (bacteriophage)
During process of viral replication, portions of the bacterial chromosome may be packaged into the bacteriophage particle
**generalized & specialized
The gene for diphtheria is carried by what?
a temperate bacteriophage
What is a bacteriophage?
Describe the lytic cycle.
Phage injects DNA into host.
New phage DNA & proteins assembled into virions.
Cell lyses & releases all the new phages.
Describe the lysogenic cycle.
Phage injects DNA into host.
DNA integrates into the chromosome becoming a prophage.
Cell normally reproduces w/ viral DNA incorporated into its genome.
Eventually, prophage excised from genome & cell enters the lytic cycle.
Describe generalized transduction.
Viral particle contains primarily bacterial DNA
Random – due to accidental packaging of host DNA
Phage DNA infects cell & happens to have the genes for an enzyme that chops up its DNA & the host DNA.
Sometimes a phage will take up bacterial DNA.
Phage infects new cell & sometimes that bacterial DNA is taken up into the host genome.
Describe specialized transduction.
Phage genome is integrated into genome (lysogenic)
Bacterial genes are those adjacent to phage genome
Prophage excised from host DNA & carries with it a host gene.
Infects a different cell.
All this new DNA is incorporated into the host genome.
What is the most common means by which bacterial cells control gene expression?
A) An addition mutation within a gene
B) Deleting or inserting triplets of nucleotides
C) Preventing translation of mRNA previously produced by RNA polymerase
D) Transcription control, most often via repressor proteins that block transcription
E) Deletion of unneeded genes
Ex: lac operon
Transformation is the transfer of DNA from a donor to a recipient cell A) By a bacteriophage-transduction B) As naked DNA in solution C) By cell-to-cell contact-conjugation D) By crossing over E) By sexual reproduction
Transformation is blocked if you put DNAse into the medium.
Generalized transduction is one way for transfer of genetic information from one bacterium to another.Which of the following is a property of generalized transduction?
A) Sensitive to the addition of DNase into the media
B) Requires both an insertion sequence and a transposase in additional to the bacterial DNA
C) Transducing phage particles contain phage DNA linked to bacterial DNA-specialized transduction
D) Transducing phage particles contain only bacterial DNA
E) The donor cell that releases the generalized transducing particles must be in contact with the recipient cell that receives the particles
D is correct.
What are the 2 types of bacteriophages? Which favor the lytic cycle? Which favor generalized transduction?
Virulent Bacteriophages–Lytic cycle-generalized transduction.
Temperate Bacteriophages–Lysogenic cycle–specialized transduction