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Questions and Answers
What are the three methods of genetic transfer in bacteria?
What are the three methods of genetic transfer in bacteria?
- Conjugation, Transduction, Transformation (correct)
- Conjugation, Binary fission, Transformation
- Binary fission, Transduction, Transformation
- Mutation, Selection, Conjugation
Vertical gene transfer in bacteria occurs between individuals that are not parents and offspring.
Vertical gene transfer in bacteria occurs between individuals that are not parents and offspring.
False (B)
Horizontal gene transfer enhances genetic diversity in bacteria and occurs between ________ that are not directly related.
Horizontal gene transfer enhances genetic diversity in bacteria and occurs between ________ that are not directly related.
individuals
Match the following methods of bacterial genetic transfer with their definitions:
Match the following methods of bacterial genetic transfer with their definitions:
Which of the following statements is true regarding allelic differences in bacteria?
Which of the following statements is true regarding allelic differences in bacteria?
E.coli is noted for having a relatively consistent genome size across all strains.
E.coli is noted for having a relatively consistent genome size across all strains.
The genetic transfer method that involves bacteriophages is called ________.
The genetic transfer method that involves bacteriophages is called ________.
Which of the following nutrients must an auxotroph obtain from its growth medium?
Which of the following nutrients must an auxotroph obtain from its growth medium?
All bacteria can undergo conjugation.
All bacteria can undergo conjugation.
What does the F factor in E. coli refer to?
What does the F factor in E. coli refer to?
The transfer of DNA from one bacterium to another via direct contact is known as __________.
The transfer of DNA from one bacterium to another via direct contact is known as __________.
Match the following auxotrophs with their respective nutrients:
Match the following auxotrophs with their respective nutrients:
During conjugation, what structure forms between the donor and recipient cells?
During conjugation, what structure forms between the donor and recipient cells?
Auxotrophs can synthesize all nutrients needed for their growth.
Auxotrophs can synthesize all nutrients needed for their growth.
What is the role of the relaxosome during conjugation?
What is the role of the relaxosome during conjugation?
In E. coli, donor strains that contain an F factor are designated as __________.
In E. coli, donor strains that contain an F factor are designated as __________.
Which of the following statements best describes auxotrophs?
Which of the following statements best describes auxotrophs?
What does MRSA stand for?
What does MRSA stand for?
Both simple transposition and retrotransposition result in the integration of transposable elements at new locations in the genome.
Both simple transposition and retrotransposition result in the integration of transposable elements at new locations in the genome.
Name the enzyme responsible for catalyzing the removal of a transposon and its reinsertion.
Name the enzyme responsible for catalyzing the removal of a transposon and its reinsertion.
Transposons can carry ___________ genes, increasing the genetic variability within bacterial populations.
Transposons can carry ___________ genes, increasing the genetic variability within bacterial populations.
Match the types of transposition to their descriptions:
Match the types of transposition to their descriptions:
What is the role of bacteriophages in transduction?
What is the role of bacteriophages in transduction?
Transformation involves the transfer of DNA through direct contact between bacterial cells.
Transformation involves the transfer of DNA through direct contact between bacterial cells.
Define what it means for a bacterial cell to be 'competent.'
Define what it means for a bacterial cell to be 'competent.'
During transformation, an extracellular nuclease cuts the DNA into smaller ______.
During transformation, an extracellular nuclease cuts the DNA into smaller ______.
Match the following steps of transformation with their descriptions:
Match the following steps of transformation with their descriptions:
What kind of DNA can bacteria uptake during transformation?
What kind of DNA can bacteria uptake during transformation?
Horizontal gene transfer can lead to antibiotic resistance in bacteria.
Horizontal gene transfer can lead to antibiotic resistance in bacteria.
What is the primary function of the exporter in bacterial conjugation?
What is the primary function of the exporter in bacterial conjugation?
Name one method through which bacteria can acquire antibiotic resistance via horizontal gene transfer.
Name one method through which bacteria can acquire antibiotic resistance via horizontal gene transfer.
The process of transformation leads to the formation of a ______ region due to sequence differences.
The process of transformation leads to the formation of a ______ region due to sequence differences.
An Hfr cell can transfer its entire chromosome in a single conjugation event.
An Hfr cell can transfer its entire chromosome in a single conjugation event.
Which of the following is NOT a characteristic of naturally competent cells?
Which of the following is NOT a characteristic of naturally competent cells?
What happens when F factor integrates into the chromosome?
What happens when F factor integrates into the chromosome?
In a conjugation event, if it occurs for a short time, only __________ will be transferred.
In a conjugation event, if it occurs for a short time, only __________ will be transferred.
What is the purpose of transduction in bacteria?
What is the purpose of transduction in bacteria?
Match the following bacterial strains with their capabilities:
Match the following bacterial strains with their capabilities:
Conjugation can be used for chromosome mapping in bacteria.
Conjugation can be used for chromosome mapping in bacteria.
Name the virus that infects bacterial cells and is involved in transduction.
Name the virus that infects bacterial cells and is involved in transduction.
The complete E. coli chromosome takes approximately __________ minutes to transfer.
The complete E. coli chromosome takes approximately __________ minutes to transfer.
Which of the following steps occurs first in the process of transduction?
Which of the following steps occurs first in the process of transduction?
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Study Notes
Genetic Transfer in Bacteria
- Bacteria, like eukaryotes, have allelic differences that influence traits.
- Allelic differences in bacteria are typically between strains, not species.
- Bacterial strains often have the same allele for a gene.
- E. coli genomes vary significantly in gene content, ranging from 4-6 Mb in size.
Horizontal Gene Transfer
- Horizontal gene transfer occurs between individuals that are not in a parent-offspring relationship.
- It enhances genetic diversity in bacteria, similar to sexual reproduction in eukaryotes.
Overview of Genetic Transfer Methods
- Conjugation: Direct physical contact between bacteria.
- Transduction: Transfer of DNA via bacteriophages.
- Transformation: Uptake of extracellular DNA from a dead bacterium.
Bacterial Conjugation: Key Players
- Joshua Lederberg & Edward Tatum: Discovered genetic transfer in bacteria in 1946.
- Auxotrophs: Bacteria unable to synthesize specific nutrients.
- F factor (fertility factor): Plasmid found in donor bacteria that allows for conjugation.
- F+ strains: Possess the F factor.
- F- strains: Lack the F factor.
Steps of Conjugation
- Contact: Donor and recipient cells connect via pili, which act as attachment sites.
- Pilus shortening: Pili shorten to bring cells closer, forming a conjugation bridge.
- Relaxosome: Recognizes the origin of transfer on the DNA and initiates cutting.
- Relaxase: Attaches to the cut end of the transfer (T) DNA.
- Exporter: Pumps T DNA and relaxase into the recipient cell.
- Replication: Both donor and recipient F factor plasmids replicate, making both cells F+.
Mapping Using Conjugation
- F' factors: Carry bacterial chromosomal genes that were originally integrated into the F factor.
- Hfr cells: Result from the F factor integrating into the bacterial chromosome.
- Hfr x F- conjugation: Transfers a portion of the Hfr chromosome, allowing for genetic mapping.
Transduction
- Bacteriophage: Virus that infects bacterial cells.
- Mispackaged phage: A phage containing host cell DNA instead of phage DNA.
- Recombination: Donor DNA integrates into the recipient cell's chromosome.
Transformation
- Competent cells: Bacteria able to take up extracellular DNA.
- Naturally competent cells: Cells that naturally take up DNA.
- Artificially competent cells: Cells made able to take up DNA through laboratory techniques.
Steps of Transformation
- Binding: DNA fragment binds to a cell surface receptor on the competent cell.
- Nuclease digestion: Extracellular nuclease cuts the DNA into smaller fragments.
- Transport: Single DNA strand enters the cell via the uptake system.
- Homologous recombination: DNA aligns with a homologous region on the bacterial chromosome and integrates.
Transformation Variations
- Nonhomologous recombination: DNA might integrate randomly into the chromosome, but it's less common.
- Species specific uptake: Bacteria tend to take up DNA released from dead bacteria of the same or related species.
- Plasmid uptake: Some naturally competent cells can also take up plasmids.
Horizontal Gene Transfer (HGT) Implications
- Antibiotic resistance: HGT plays a significant role in the spread of antibiotic resistance.
- MRSA (Methicillin-resistant Staphylococcus aureus): Strains resistant to penicillin and methicillin, causing serious skin infections.
Transposition
- Transposons: Small mobile DNA segments.
- Transposase: Enzyme that catalyzes the removal and reinsertion of transposons.
- Inverted repeats: Identical DNA sequences that run in opposite directions, flanking transposons.
Types of Transposition
- Simple transposition (“cut-and-paste"): Transposon is excised and inserted at a new location.
- Retrotransposition (“copy-and-paste"): A copy of the transposon is inserted at a new location, while the original remains.
Why Do Transposons Exist?
- Selfish DNA Theory: Transposons increase in frequency unless they significantly harm the host.
- Potential advantage: Transposons may carry antibiotic-resistance genes and contribute to genetic variability.
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