Question

The proof that DNA, not protein, is the carrier of genetic information involved a number of historical experiments, including transformation or horizontal gene transfer (HGT), which is the uptake and expression of extracellular DNA. A. As described in Figure 14.3, transformation or HGT was first reported by Griffith in 1928 in an experiment in which the following occurred: 1. heat-treated, pathogenic bacteria recovered their pathogenicity when incubated with non pathogenic bacteria 2. plasmids were transferred to nonpathogenic bacteria from pathogenic bacteria through conjugation 3. non pathogenic bacteria acquired pathogenicity when incubated in a broth containing heat treated, pathogenic bacteria 4. polysaccharide cell capsules from pathogenic bacteria were transferred to non pathogenic bacteria B. Griffith’s experiment, however, left undetermined the identity of the cellular component that encoded genetic information. The identity of DNA as the carrier of genetic information was resolved through the experiments by Martha Chase and Alfred Hershey because they observed the following: 1. injections with a serum containing chemically isolated polysaccharides and non pathogenic bacteria were not lethal 2. pathogenic bacterial DNA that was radioactively labeled using a phosphorus isotope was not present in mice that died 3. bacteriophages from a bacterial culture grown in a nutrient-containing medium and radioactively labeled using a sulfur isotope transferred the label to bacteria incubated in an unlabeled nutrient-containing medium 4. bacteriophages from a bacterial culture grown in a nutrient-containing medium and radioactively labeled using a sulfur isotope did not transfer the label to bacteria incubated in an unlabeled nutrient-containing medium C. Transformation and transduction increase variation within populations of bacteria and archaebacteria by the following: a. transferring DNA among different species b. transferring free DNA across the cell membrane without energy expenditure c. transferring DNA between different strains of the same species of bacteria d. phagocytosis of bacteriophages The evolution of antibiotic resistance via HGT poses a challenge to medical technology. On the other hand, transformation is often assayed by incorporating an antibiotic-resistance gene in the plasmid to be transferred into the host organism. In natural environments, bacterial and archaebacterial cells become competent (able to transport DNA through the cytoplasmic membrane) in response to stress such as UV radiation, high population density, or heat shock. Such conditions are often difficult to model in the laboratory, where competence can be induced by high concentrations of divalent cations, $Ca^{+2}$ or $Mg^{+2},$ or electrical shock. In either setting, extracellular DNA can be transported into the cell, and (to a good approximation) uptake is proportional to the concentration of extracellular DNA. D. Identify a factor that might affect transformation or HGT. Then, design a plan to evaluate the dependence of transformational efficiency (defined as the number of transformations per gram of extracellular DNA) of plasmids that transfer antibiotic resistance to a particular strain of Escherichia coli that is not resistant on that factor.

Name: Problem 70, Chapter 14: Biology for AP Courses
Uploaded: 2019-07-29T20:26:43-08:00
Duration: 3 min 7 s
Channel: Grant Castaneda

A. As described in Figure 14.3, transformation or HGT was first reported by Griffith in 1928 in an experiment in which the following occurred:

1. heat-treated, pathogenic bacteria recovered their pathogenicity when incubated with non pathogenic bacteria
2. plasmids were transferred to nonpathogenic bacteria from pathogenic bacteria through conjugation
3. non pathogenic bacteria acquired pathogenicity when incubated in a broth containing heat treated, pathogenic bacteria
4. polysaccharide cell capsules from pathogenic bacteria were transferred to non pathogenic bacteria

B. Griffith’s experiment, however, left undetermined the identity of the cellular component that encoded genetic information. The identity of DNA as the carrier of genetic information was resolved through the experiments by Martha Chase and Alfred Hershey because they observed the following:

1. injections with a serum containing chemically isolated polysaccharides and non pathogenic bacteria were not lethal
2. pathogenic bacterial DNA that was radioactively labeled using a phosphorus isotope was not present in mice that died
3. bacteriophages from a bacterial culture grown in a nutrient-containing medium and radioactively labeled using a sulfur isotope transferred the label to bacteria incubated in an unlabeled nutrient-containing medium
4. bacteriophages from a bacterial culture grown in a nutrient-containing medium and radioactively labeled using a sulfur isotope did not transfer the label to bacteria incubated in an unlabeled nutrient-containing medium

C. Transformation and transduction increase variation within populations of bacteria and archaebacteria by the following:

a. transferring DNA among different species
b. transferring free DNA across the cell membrane without energy expenditure
c. transferring DNA between different strains of the same species of bacteria
d. phagocytosis of bacteriophages

The evolution of antibiotic resistance via HGT poses a challenge to medical technology. On the other hand, transformation is often assayed by incorporating an antibiotic-resistance gene in the plasmid to be transferred into the host organism. In natural environments, bacterial and archaebacterial cells become competent (able to transport DNA through the cytoplasmic membrane) in response to stress such as UV radiation, high population density, or heat shock. Such conditions are often difficult
to model in the laboratory, where competence can be induced by high concentrations of divalent cations, $Ca^{+2}$ or $Mg^{+2},$ or electrical shock. In either setting, extracellular DNA can be transported into the cell, and (to a good approximation) uptake is proportional to the concentration of extracellular DNA.

D. Identify a factor that might affect transformation or HGT. Then, design a plan to evaluate the dependence of transformational efficiency (defined as the number of transformations per gram of extracellular DNA) of plasmids that transfer antibiotic resistance to a particular strain of Escherichia coli that is not resistant on that factor.

Biology for AP Courses

Julianne Zedalis,…

Chapter 14, Problem 70

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Solved by Expert Grant Castaneda

07/29/2019

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The correct answer is option 3: non pathogenic bacteria acquired pathogenicity when incubated in a broth containing heat treated, pathogenic bacteria. This is because Griffith's experiment involved heat-killing pathogenic bacteria and mixing them with Show more…

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The proof that DNA, not protein, is the carrier of genetic information involved a number of historical experiments, including transformation or horizontal gene transfer (HGT), which is the uptake and expression of extracellular DNA. A. As described in Figure 14.3, transformation or HGT was first reported by Griffith in 1928 in an experiment in which the following occurred: 1. heat-treated, pathogenic bacteria recovered their pathogenicity when incubated with non pathogenic bacteria 2. plasmids were transferred to nonpathogenic bacteria from pathogenic bacteria through conjugation 3. non pathogenic bacteria acquired pathogenicity when incubated in a broth containing heat treated, pathogenic bacteria 4. polysaccharide cell capsules from pathogenic bacteria were transferred to non pathogenic bacteria B. Griffith’s experiment, however, left undetermined the identity of the cellular component that encoded genetic information. The identity of DNA as the carrier of genetic information was resolved through the experiments by Martha Chase and Alfred Hershey because they observed the following: 1. injections with a serum containing chemically isolated polysaccharides and non pathogenic bacteria were not lethal 2. pathogenic bacterial DNA that was radioactively labeled using a phosphorus isotope was not present in mice that died 3. bacteriophages from a bacterial culture grown in a nutrient-containing medium and radioactively labeled using a sulfur isotope transferred the label to bacteria incubated in an unlabeled nutrient-containing medium 4. bacteriophages from a bacterial culture grown in a nutrient-containing medium and radioactively labeled using a sulfur isotope did not transfer the label to bacteria incubated in an unlabeled nutrient-containing medium C. Transformation and transduction increase variation within populations of bacteria and archaebacteria by the following: a. transferring DNA among different species b. transferring free DNA across the cell membrane without energy expenditure c. transferring DNA between different strains of the same species of bacteria d. phagocytosis of bacteriophages The evolution of antibiotic resistance via HGT poses a challenge to medical technology. On the other hand, transformation is often assayed by incorporating an antibiotic-resistance gene in the plasmid to be transferred into the host organism. In natural environments, bacterial and archaebacterial cells become competent (able to transport DNA through the cytoplasmic membrane) in response to stress such as UV radiation, high population density, or heat shock. Such conditions are often difficult to model in the laboratory, where competence can be induced by high concentrations of divalent cations, $Ca^{+2}$ or $Mg^{+2},$ or electrical shock. In either setting, extracellular DNA can be transported into the cell, and (to a good approximation) uptake is proportional to the concentration of extracellular DNA. D. Identify a factor that might affect transformation or HGT. Then, design a plan to evaluate the dependence of transformational efficiency (defined as the number of transformations per gram of extracellular DNA) of plasmids that transfer antibiotic resistance to a particular strain of Escherichia coli that is not resistant on that factor.

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Key Concepts

Experimental Design in Studying Transformation Efficiency

Designing experiments to evaluate transformation efficiency involves systematically varying conditions (such as ion concentrations or physical shock) that influence the uptake of extracellular DNA. This approach requires careful control of variables, precise measurement of the amount of DNA and the number of transformants, and ultimately aids in understanding factors that affect genetic transformation in bacteria.

Transformation/HGT

Transformation, a form of horizontal gene transfer, refers to the process by which bacteria take up extracellular DNA from their environment. This concept is key in understanding how genetic information can be exchanged between cells without cell-to-cell contact, driving genetic diversity and evolution in microbial populations.

Griffith's Experiment

Griffith’s experiment was a foundational study in molecular biology that demonstrated the phenomenon of transformation. By showing that a non-pathogenic strain could acquire pathogenic traits when exposed to heat-killed pathogenic bacteria, it provided the first evidence that a 'transforming principle' existed, which later was identified as DNA.

Chase and Hershey Experiments

The experiments by Chase and Hershey were crucial in establishing DNA as the molecule responsible for heredity. By using radioactive isotopes to label DNA and protein, they demonstrated that DNA, not protein, was the genetic material transferred by bacteriophages, thereby resolving a major question about the nature of the transforming principle.

Bacterial Competence

Bacterial competence refers to the physiological state of bacteria that enables them to take up extracellular DNA from their environment. This state can be naturally induced by environmental stress conditions or artificially induced in the laboratory, and it is critically important for the process of transformation and the study of gene function.

Plasmids and Antibiotic Resistance

Plasmids are small, circular DNA molecules that can replicate independently of the bacterial chromosome. They often carry genes that confer antibiotic resistance and can be horizontally transferred between bacteria. This concept is fundamental in understanding how antibiotic resistance spreads in microbial populations and poses challenges to medical treatment.

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