62 Questions
What is the purpose of Appendix A?
To describe methods for growing bacteria in a laboratory
Where can one find general methods for growing bacteria in a laboratory?
In the appendices
What is the role of Appendix A in the context of bacterial growth?
To describe laboratory methods for bacterial growth
What is the relationship between the main text and Appendix A?
Appendix A supplements the main text
What type of information is typically found in an appendix?
Supporting information and supplementary data
What is the purpose of including an appendix in a document?
To provide additional information that supports the main idea
What can be inferred about the content of the main text?
It presents an overview of bacterial growth methods
What is the main benefit of using Hfr strains in conjugation and mapping?
They enable precise mapping of genetic traits
Who is credited with the discovery of a strain of E. coli that led to the development of conjugation and mapping techniques?
Luca Cavalli-Sforza
What is the primary mechanism by which Hfr strains facilitate genetic transfer?
Conjugation
What is the main advantage of using Hfr strains over other bacterial strains in genetic mapping?
Increased precision of genetic mapping
What is the significance of the 1950s in the context of conjugation and mapping via Hfr strains?
The period when Luca Cavalli-Sforza discovered the Hfr strain
What is the primary application of conjugation and mapping via Hfr strains?
Genetic mapping of bacterial traits
What is the role of Luca Cavalli-Sforza's discovery in the development of modern genetic mapping techniques?
It facilitated the development of conjugation and mapping techniques
What percentage of bacterial cells with thr+leu+ genotype survived after 20 minutes of conjugation?
100%
At what time interval did the bacterial cells with lac+ genotype start to show significant survival?
30 minutes
What is the percentage of bacterial cells with gal+ genotype that survived after 60 minutes of conjugation?
27%
After how many minutes of conjugation did the bacterial cells with azis genotype show 50% survival?
15 minutes
What is the percentage of bacterial cells with tons genotype that survived after 50 minutes of conjugation?
78%
At what time interval did the bacterial cells with thr+leu+ genotype show 100% survival?
10 minutes and above
What is the relationship between the time of conjugation and the percentage of survival of bacterial cells with different genotypes?
The percentage of survival increases with the time of conjugation.
What is the primary assumption underlying the interrupted conjugation technique?
The time it takes genes to enter the recipient cell is directly related to their order along the bacterial chromosome
What is the role of streptomycin in the interrupted conjugation experiment?
To kill the donor Hfr cells following conjugation
What is the genetic composition of the donor Hfr strain?
thr +, leu +, azi s, ton s, lac +, gal +, str s
What was the primary goal of Wollman and Jacob's experiment?
To determine the order of genes along the bacterial chromosome
What is the significance of the thr + and leu + genes in the experiment?
They are transferred first, in that order, within 5 to 10 minutes of mating
How is the order of genes along the chromosome determined in the interrupted conjugation technique?
By determining the time it takes for genes to enter the recipient cell
What is the significance of the conjugation time in the interrupted conjugation technique?
It is directly related to the order of genes along the bacterial chromosome
What is the shape of the E. coli chromosome?
Circular
Which of the following organisms has a circular chromosome?
E. coli
What is the characteristic of the E. coli chromosome?
It is circular and small
Which of the following is true about the E. coli chromosome?
It is composed of DNA
What is the genetic material found in the E. coli chromosome?
DNA
Which of the following is a characteristic of the E. coli genetic material?
It is circular
What is the shape of the genetic material found in E. coli?
Circular
Which of the following is true about the E. coli genetic material?
It is composed of a single molecule
What is the structure of the E. coli genetic material?
A single circular molecule
What is the primary purpose of an interrupted conjugation experiment?
To compute the approximate time of entry of genes onto the chromosome
What is the significance of the x-axis in an interrupted conjugation experiment?
It represents the time of entry of genes onto the chromosome
What is the relationship between the time of entry and the distance between genes?
The time of entry determines the distance between genes
What is the primary assumption underlying the interrupted conjugation technique?
That the genes are transferred in a specific order during conjugation
What is the significance of the distance between genes in an interrupted conjugation experiment?
It determines the order of genes along the chromosome
What is the primary reason for interrupting conjugations at different times?
To determine the order of genes along the chromosome
What is the significance of the thr+ and leu+ genes in the experiment?
They are the first genes to be transferred during conjugation
Why is streptomycin used in the interrupted conjugation experiment?
To kill the donor Hfr cells following conjugation
What is the significance of the linear transfer of the Hfr chromosome?
It allows for the determination of the order of genes along the chromosome
What is the primary goal of Wollman and Jacob's experiment?
To determine the order of genes along the chromosome
What is the primary function of the origin of transfer of the integrated F factor?
To determine the direction of the transfer of the Hfr chromosome
What is the typical duration of the conjugation process between Hfr and F- strains?
1.5 to 2 hours
What is the genotype of the Hfr cell in terms of lactose metabolism?
lac +
What is the result of the recombination of chromosomal material between Hfr and F- cells?
The exchange of genetic material between homologous regions on the chromosomes
What is the direction of the transfer of the Hfr chromosome during conjugation?
From the Hfr cell to the F- cell in a linear manner
What is the significance of conjugation experiments in the context of E. coli?
To map genes on the E. coli chromosome
How many genes have been mapped on the E. coli chromosome using conjugation experiments?
1,000
What is the primary focus of conjugation experiments with E. coli?
Genetic transfer between bacteria
What is the significance of the E. coli chromosome in the context of conjugation experiments?
It is relevant to genetic transfer between bacteria
What can be inferred about the E. coli chromosome from conjugation experiments?
It is a circular chromosome
What is the primary location where general methods for growing bacteria in a laboratory are described?
Appendix A
What is the significance of Appendix A in the context of bacterial growth?
It describes the general methods for growing bacteria in a laboratory
What type of information is typically found in an appendix, as seen in the context of bacterial growth?
General methods for growing bacteria in a laboratory
What can be inferred about the content of the main text, given the presence of Appendix A?
It does not cover general methods for growing bacteria in a laboratory
What is the relationship between the main text and Appendix A, in the context of bacterial growth?
The main text does not cover general methods, which are instead described in Appendix A
Study Notes
Conjugation and Mapping via Hfr Strains
- Luca Cavalli-Sforza discovered a strain of E. coli in the 1950s
- Elie Wollman and François Jacob developed the interrupted conjugation technique in the 1950s
- The technique is based on the idea that the time it takes for genes to enter the recipient cell is directly related to their order along the bacterial chromosome
- The Hfr chromosome is transferred linearly to the F- recipient cell, allowing the order of genes to be deduced by interrupting conjugations at different times
Strains for Interrupted Mating
- The donor (Hfr) strain genetic composition: • thr+: Able to synthesize the essential amino acid threonine • leu+: Able to synthesize the essential amino acid leucine • azi s: Sensitive to killing by azide (a toxic chemical) • ton s: Sensitive to infection by T1 (a bacterial virus) • lac+: Able to metabolize lactose and use it for growth • gal+: Able to metabolize galactose and use it for growth • str s: Sensitive to killing by streptomycin (an antibiotic)
- The recipient F- strain had the opposite genotype: • thr-: Unable to synthesize the essential amino acid threonine • leu-: Unable to synthesize the essential amino acid leucine • azi r: Resistant to killing by azide (a toxic chemical) • ton r: Resistant to infection by T1 (a bacterial virus) • lac-: Unable to metabolize lactose and use it for growth • gal-: Unable to metabolize galactose and use it for growth • str r: Resistant to killing by streptomycin (an antibiotic)
The Goal and Achieving It
- Wollman and Jacob's goal was to determine the times at which genes azi s, ton s, lac+, and gal+ were transferred
- The transfer of the str s was not examined due to the use of streptomycin to kill the donor (Hfr) cell following conjugation
- The recipient F- cell is streptomycin resistant
The Data
- The table shows the percentage of surviving colonies with different genotypes at varying conjugation times
- The data shows the order of gene transfer, with thr+ and leu+ transferred first, followed by azi s, ton s, lac+, and gal+
Interrupted Conjugation Experiment
- The experiment determines the distance between genes by comparing their times of entry during conjugation.
- The approximate time of entry is computed by extrapolating the time back to the x-axis.
- In this example, two genes are approximately 9 minutes apart along the E. coli chromosome.
Conjugation between Hfr and F- Strains
- Conjugation between an Hfr and an F- strain involves the transfer of a portion of the Hfr bacterial chromosome.
- The origin of transfer of the integrated F factor determines the starting point and direction of the transfer process.
- When the DNA is cut, or nicked, at this site, it becomes the starting point for the transfer of the Hfr chromosome to the F- cell.
- A strand of bacterial DNA begins to enter the recipient cell in a linear manner.
Characteristics of Conjugation
- It generally takes about 1.5 to 2 hours for the entire Hfr chromosome to be passed into the F- cell.
- Most conjugations do not last that long, and only a portion of the Hfr chromosome gets into the F- cell.
- Chromosomal material from the Hfr cell can recombine with the homologous region on the chromosome of the recipient cell.
Genotype of Hfr and F- Cells
- The genotype of the Hfr cell is: lac + (ability to metabolize lactose), pro + (ability to synthesize proline).
- The genotype of the F- cell is: lac - (inability to metabolize lactose), pro - (inability to synthesize proline).
Experiment 7A Interrupted Conjugation Technique
- Developed by Elie Wollman and François Jacob in the 1950s.
- The rationale behind this mapping strategy is that the time it takes genes to enter the recipient cell is directly related to their order along the bacterial chromosome.
- The Hfr chromosome is transferred linearly to the F- recipient cell.
- Interrupting conjugations at different times leads to various lengths being transferred.
- The order of genes along the chromosome can be deduced by determining the genes transferred during short conjugations versus those transferred during long conjugations.
Strains for Interrupted Mating
- The donor (Hfr) strain genetic composition:
- thr + (able to synthesize threonine)
- leu + (able to synthesize leucine)
- azi s (sensitive to killing by azide)
- ton s (sensitive to infection by T1)
- lac + (able to metabolize lactose)
- gal + (able to metabolize galactose)
- str s (sensitive to killing by streptomycin)
- The recipient F- strain has the opposite genotype:
- thr - (unable to synthesize threonine)
- leu - (unable to synthesize leucine)
- azi r (resistant to killing by azide)
- ton r (resistant to infection by T1)
- lac - (unable to metabolize lactose)
- gal - (unable to metabolize galactose)
- str r (resistant to killing by streptomycin)
The Goal of Wollman and Jacob's Experiment
- Wollman and Jacob already knew that:
- The thr + and leu + genes were transferred first, in that order.
- Both were transferred within 5 to 10 minutes of mating.
- The goal was to determine the times at which genes azi s, ton s, lac +, and gal + were transferred.
- The transfer of the str s was not examined, as streptomycin was used to kill the donor (Hfr) cell following conjugation.
Achieving the Goal
- Conjugation experiments have been used to map more than 1,000 genes on the E. coli chromosome.
Explore the process of conjugation and mapping via Hfr strains in bacteria, as discovered by Luca Cavalli-Sforza in the 1950s.
Make Your Own Quizzes and Flashcards
Convert your notes into interactive study material.
Get started for free
