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Questions and Answers
What is the term used to describe an organism that is genetically distinct from the normal members of a species?
What is the term used to describe an organism that is genetically distinct from the normal members of a species?
- Competent
- Wild type
- Transformant
- Mutant (correct)
Which type of transformation involves bacteria taking up DNA naturally without special treatments?
Which type of transformation involves bacteria taking up DNA naturally without special treatments?
- Induced transformation
- Artificial transformation
- Natural transformation (correct)
- Active transformation
What term is used to refer to bacteria that can take up DNA only at certain stages in their lifecycle?
What term is used to refer to bacteria that can take up DNA only at certain stages in their lifecycle?
- Clonal
- Competent (correct)
- Resistant
- Transformant
What was the significance of the discovery involving Streptococcus pneumoniae?
What was the significance of the discovery involving Streptococcus pneumoniae?
Which of the following statements accurately describes induced transformation?
Which of the following statements accurately describes induced transformation?
What role do competence pheromones play in bacterial behavior?
What role do competence pheromones play in bacterial behavior?
Which method is commonly used to artificially induce competence in bacteria?
Which method is commonly used to artificially induce competence in bacteria?
What is quorum sensing in bacteria primarily used for?
What is quorum sensing in bacteria primarily used for?
Which of the following statements about plasmids in transformation is true?
Which of the following statements about plasmids in transformation is true?
What is the role of electroporation in genetic engineering of bacteria?
What is the role of electroporation in genetic engineering of bacteria?
What characteristic distinguishes rough type bacteria from smooth type bacteria?
What characteristic distinguishes rough type bacteria from smooth type bacteria?
In Griffith's experiment, what was the significance of the 'transforming principle'?
In Griffith's experiment, what was the significance of the 'transforming principle'?
What is the first step in the DNA uptake process for Gram-negative bacteria?
What is the first step in the DNA uptake process for Gram-negative bacteria?
Which of the following is NOT a possible outcome for ssDNA once it enters a bacterial cell?
Which of the following is NOT a possible outcome for ssDNA once it enters a bacterial cell?
How do Gram-positive bacteria differ in DNA uptake when compared to Gram-negative bacteria?
How do Gram-positive bacteria differ in DNA uptake when compared to Gram-negative bacteria?
Which type of pilus is involved in the DNA transfer process in bacteria?
Which type of pilus is involved in the DNA transfer process in bacteria?
What happens during the movement of DNA across a Gram-negative bacterium's cell wall?
What happens during the movement of DNA across a Gram-negative bacterium's cell wall?
What is the main function of retracting the pilus in bacteria during DNA uptake?
What is the main function of retracting the pilus in bacteria during DNA uptake?
Which of the following statements is true about DNA uptake in Gram-positive bacteria?
Which of the following statements is true about DNA uptake in Gram-positive bacteria?
What is one reason bacteria might take up foreign DNA?
What is one reason bacteria might take up foreign DNA?
Why might some bacteria only take up DNA from their own species?
Why might some bacteria only take up DNA from their own species?
How do most naturally transformable bacteria regulate competence?
How do most naturally transformable bacteria regulate competence?
Which of these bacteria are known to require a DNA uptake sequence (DUS) for DNA uptake?
Which of these bacteria are known to require a DNA uptake sequence (DUS) for DNA uptake?
What is the role of competence pheromones in bacteria?
What is the role of competence pheromones in bacteria?
What function could DNA recombination serve for bacteria?
What function could DNA recombination serve for bacteria?
What process occurs when a sensor kinase detects a signal in bacteria?
What process occurs when a sensor kinase detects a signal in bacteria?
Why is it harder for bacteria to degrade DNA after uptake compared to degrading it outside?
Why is it harder for bacteria to degrade DNA after uptake compared to degrading it outside?
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Study Notes
Transformation
- Wild-type (WT) refers to the normal organism, while Mutant (∆) is the organism with a genetic difference from the normal.
- Transformation is the process where bacteria directly take up "naked" DNA from the environment.
- Natural Transformation occurs when bacteria can uptake DNA without specific treatments.
- Natural competence (ability to take up DNA) is a stage-dependent process.
- Naturally competent bacteria can achieve competence on their own, while induced transformation requires specific treatments.
- Induced transformation uses chemical treatments or electrical fields to enhance DNA permeability.
- Discovery of Transformation:
- Griffith's Experiment: showed that dead pathogenic bacteria could transfer a "transforming principle" to live, non-pathogenic bacteria, turning them pathogenic.
- Avery, McCarty, and MacLeod: identified the transforming principle as DNA.
- DNA Uptake:
- Can be species-specific or nonspecific.
- Gram-negative bacteria (Proteobacteria):
- DNA binds to the outer cell surface.
- DNA moves across the cell wall and outer membrane.
- One DNA strand is degraded by nucleases.
- The single-stranded DNA translocates across the inner membrane.
- Gram-positive bacteria (Firmicutes):
- Similar process to Gram-negatives, but lacks the outer membrane, so DNA passes through the cell wall and cell membrane.
- Reasons for DNA Uptake:
- Nutrition: DNA can be a nutrient source, but degrading it inside is less efficient than outside.
- Repair: DNA can be used to repair damaged DNA, but competence isn't always induced in response to damage.
- Recombination: Enables genetic reassortment for survival.
- Competence Pheromones:
- Competence genes are expressed by most naturally transformable bacteria.
- B.subtilis uses a two-component system (sensor kinase and response regulator) to regulate competence.
- Competence pheromones are small peptides secreted by bacteria, increasing in concentration as bacteria multiply.
- High concentrations induce competence.
- Quorum sensing involves small molecules signaling high density.
Artificially Induced Competence
- Can be induced in bacteria that are not naturally competent.
- Plasmids are more efficient than linear DNA fragments.
- Chemically induced competence: uses calcium ions to make bacteria more permeable.
- Electroporation uses a brief electric field to alter the surface charge, allowing DNA to enter.
Homologous Recombination
- Double-stranded break repair: refers to the process of repairing broken DNA.
- Molecular Genetics at Work:
- Engineered altered genes are introduced into bacteria using plasmids and transformation.
- Example: A Kanamycin resistance gene (Kanr) is inserted into a gene of interest, creating a mutated gene.
- Homologous recombination is used to integrate the plasmid, duplicating the inserted region.
- Another recombination event removes the plasmid, leaving the mutated gene in the chromosome.
- The resulting cells are Kanr and lack the functional gene.
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