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Questions and Answers
Which of the following best describes the contribution of T.H. Morgan to the understanding of DNA?
Which of the following best describes the contribution of T.H. Morgan to the understanding of DNA?
- Established that genes are located on chromosomes. (correct)
- Developed the double helix model of DNA.
- Discovered the transforming principle in bacteria.
- Confirmed that DNA, not protein, is the genetic material.
Frederick Griffith's experiment involving the injection of different strains of Streptococcus pneumoniae into mice demonstrated which of the following principles?
Frederick Griffith's experiment involving the injection of different strains of Streptococcus pneumoniae into mice demonstrated which of the following principles?
- The structure of DNA is a double helix.
- Harmless bacteria can become pathogenic through transformation. (correct)
- DNA is the genetic material.
- Proteins are responsible for causing pneumonia.
Which component was critical in Avery, McCarty, and MacLeod's experiment to identify the 'transforming principle'?
Which component was critical in Avery, McCarty, and MacLeod's experiment to identify the 'transforming principle'?
- Purified DNA and proteins (correct)
- Radioactive isotopes
- Heat-killed bacteria
- Electron microscopy
In the Hershey and Chase experiment, bacteriophages were grown in two separate media, one containing $^{35}$S and the other containing $^{32}$P. What was the purpose of using these radioactive isotopes?
In the Hershey and Chase experiment, bacteriophages were grown in two separate media, one containing $^{35}$S and the other containing $^{32}$P. What was the purpose of using these radioactive isotopes?
What was the most important conclusion from the Hershey and Chase experiment?
What was the most important conclusion from the Hershey and Chase experiment?
Erwin Chargaff's rules state that in DNA, the amount of adenine (A) is equal to thymine (T), and the amount of guanine (G) is equal to cytosine (C). How did this contribute to the discovery of DNA structure?
Erwin Chargaff's rules state that in DNA, the amount of adenine (A) is equal to thymine (T), and the amount of guanine (G) is equal to cytosine (C). How did this contribute to the discovery of DNA structure?
Which of the following best describes the role of Rosalind Franklin in the discovery of the structure of DNA?
Which of the following best describes the role of Rosalind Franklin in the discovery of the structure of DNA?
What concept about DNA structure is supported by the phrase “It has not escaped our notice that the specific pairing we have postulated immediately suggests a possible copying mechanism for the genetic material”?
What concept about DNA structure is supported by the phrase “It has not escaped our notice that the specific pairing we have postulated immediately suggests a possible copying mechanism for the genetic material”?
The Meselson and Stahl experiment distinguished between three models of DNA replication: conservative, semiconservative, and dispersive. Which experimental result allowed them to rule out the conservative model after one round of replication?
The Meselson and Stahl experiment distinguished between three models of DNA replication: conservative, semiconservative, and dispersive. Which experimental result allowed them to rule out the conservative model after one round of replication?
In the Meselson and Stahl experiment, how did the results after two generations of replication support the semiconservative model of DNA replication?
In the Meselson and Stahl experiment, how did the results after two generations of replication support the semiconservative model of DNA replication?
How have the collective discoveries related to DNA advanced the field of biology? (Select all that apply)
How have the collective discoveries related to DNA advanced the field of biology? (Select all that apply)
Central dogma describes the flow of genetic material. How is the replication aspect of the dogma best defined?
Central dogma describes the flow of genetic material. How is the replication aspect of the dogma best defined?
The scientific community initially thought protein was the genetic material. Why was DNA later accepted instead?
The scientific community initially thought protein was the genetic material. Why was DNA later accepted instead?
Based on Chargaff's rules, if a sample of DNA contains 22% adenine, what percentage of guanine would you expect to find?
Based on Chargaff's rules, if a sample of DNA contains 22% adenine, what percentage of guanine would you expect to find?
What is the consequence of the statement "Genes are on chromosomes?"
What is the consequence of the statement "Genes are on chromosomes?"
What key observation about X-chromosome in male Drosophila did T.H. Morgan make?
What key observation about X-chromosome in male Drosophila did T.H. Morgan make?
What was the critical contribution of the Meselson-Stahl experiment to our understanding of DNA replication?
What was the critical contribution of the Meselson-Stahl experiment to our understanding of DNA replication?
What direct evidence did Avery, McCarty, and MacLeod provide to support DNA as the 'transforming principle'?
What direct evidence did Avery, McCarty, and MacLeod provide to support DNA as the 'transforming principle'?
How did Chargaff's rules specifically influence the determination of DNA's double helix structure by Watson and Crick?
How did Chargaff's rules specifically influence the determination of DNA's double helix structure by Watson and Crick?
How would the results of the Meselson-Stahl experiment differ if DNA replication was dispersive instead of semiconservative after the first replication?
How would the results of the Meselson-Stahl experiment differ if DNA replication was dispersive instead of semiconservative after the first replication?
What was the contribution of Frederick Griffith's experiment in 1928 to our understanding of genetics?
What was the contribution of Frederick Griffith's experiment in 1928 to our understanding of genetics?
In the Hershey-Chase experiment, why were bacteriophages used rather than eukaryotic cells?
In the Hershey-Chase experiment, why were bacteriophages used rather than eukaryotic cells?
Based on the image, what can be concluded about the relationship of DNA and chromosomes?
Based on the image, what can be concluded about the relationship of DNA and chromosomes?
What would the scientists in 1950s have needed to confirm the central dogma?
What would the scientists in 1950s have needed to confirm the central dogma?
Which of the following experiments provided the strongest evidence that DNA is the genetic material rather than protein?
Which of the following experiments provided the strongest evidence that DNA is the genetic material rather than protein?
What aspect of the 'central dogma' is represented in the image?
What aspect of the 'central dogma' is represented in the image?
If Meselson and Stahl had continued their experiment for a third generation, how would the ratios of the DNA bands have changed on the cesium chloride gradient related DNA samples?
If Meselson and Stahl had continued their experiment for a third generation, how would the ratios of the DNA bands have changed on the cesium chloride gradient related DNA samples?
How did 'transformation' described by Frederick Griffith influence and help with later experiments done by Avery, McCarty, and MacLeod?
How did 'transformation' described by Frederick Griffith influence and help with later experiments done by Avery, McCarty, and MacLeod?
Which of the following models can be used to explain how genes are on chromosomes?
Which of the following models can be used to explain how genes are on chromosomes?
Flashcards
Genes on chromosomes
Genes on chromosomes
Genes are located on chromosomes and are responsible for inherited traits.
Transforming Principle
Transforming Principle
Griffith's experiment showed that a substance from dead bacteria could transform live bacteria.
DNA as Transforming Factor
DNA as Transforming Factor
DNA, not protein, is the molecule responsible for the transforming principle.
Bacteriophage
Bacteriophage
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Hershey-Chase Experiment
Hershey-Chase Experiment
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Chargaff's Rules
Chargaff's Rules
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Double Helix Model
Double Helix Model
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Semi-conservative Replication
Semi-conservative Replication
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Central Dogma
Central Dogma
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Genetic Material
Genetic Material
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DNA primary synthesis roles
DNA primary synthesis roles
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Study Notes
- DNA serves as the genetic material.
Scientific History
- Significant progress has been made in understanding that DNA is the genetic material.
- T.H. Morgan contributed to this understanding in 1908.
- Frederick Griffith contributed in 1928 to the understanding that DNA is the genetic material
- Avery, McCarty, and MacLeod furthered this understanding in 1944.
- Erwin Chargaff enhanced this knowledge in 1947.
- Hershey and Chase added to this understanding in 1952.
- Watson and Crick made significant contributions in 1953.
- Meselson and Stahl completed this understanding in 1958.
Chromosomes and Phenotype
- T.H. Morgan researched Drosophila (fruit flies).
- Morgan linked specific phenotypes to specific chromosomes.
- A white-eyed male fruit fly had a specific X chromosome.
Genes and Chromosomes
- Morgan concluded that genes reside on chromosomes.
- Initially, proteins were thought to be the genetic material.
The "Transforming Principle"
- Frederick Griffith worked with Streptococcus pneumoniae bacteria, seeking a pneumonia cure.
- Harmless live bacteria mixed with heat-killed pathogenic bacteria caused fatal disease in mice.
- A substance transferred from dead bacteria could transform live bacteria, altering its phenotype.
- This phenomenon is the "Transforming Principle."
Transformation Explained
- Transformation involves a change in phenotype.
- Heat-killed bacteria retain the ability to transmit disease-causing properties.
DNA as the Transforming Principle
- Avery, McCarty, and MacLeod purified DNA and proteins from Streptococcus pneumoniae.
- Protein injected into bacteria had no effect.
- DNA injected into bacteria transformed harmless bacteria into virulent bacteria.
Avery, McCarty, & MacLeod Conclusion
- The first experimental proof emerged that DNA is the genetic material.
Confirmation of DNA
- Hershey and Chase used a classic "blender" experiment to confirm DNA's role
- The experiment involved bacteriophages, viruses infecting bacteria.
- They grew phage viruses in two media, radioactively labeling them with either 35S in their proteins, or 32P in their DNA.
- They then infected bacteria with these labeled phages.
Radioactive Phage Experiment
- 35S phage: radioactive proteins stayed in the supernatant, so viral protein did not enter the bacteria.
- 32P phage: radioactive DNA stayed in the pellet, so viral DNA did enter the bacteria.
- This confirmed that DNA is the “transforming factor.”
Chargaff's Rules
- DNA composition varies by species.
- The four bases in DNA are not present in equal quantities.
- Bases are present in a characteristic ratio.
- In humans, A=30.9%, T=29.4%, G=19.9%, C=19.8.%.
DNA Structure
- Watson and Crick developed the double helix model of DNA.
- Rosalind Franklin, Maurice Wilkins, and Linus Pauling were other scientists working on the question.
DNA Replication
- Base pairing suggests that each DNA side can serve as a template for a new strand.
- "It has not escaped our notice that the specific pairing we have postulated immediately suggests a possible copying mechanism for the genetic material." - Watson & Crick
Models of DNA Replication
- There are alternative models for how DNA is replicated.
Semiconservative Replication: Meselson & Stahl
- "Parent" nucleotides in DNA strands are labeled with heavy nitrogen (15N)
- New nucleotides are labeled with a lighter isotope (14N)
Predictions for Replication
- 15N DNA strands replicate in 14N medium, and bands should be identified after the first round of replication.
- Bands should also be identified after the second round.
Scientific History Summary
- T.H. Morgan, in 1908, discovered that genes are on chromosomes.
- Frederick Griffith, in 1928, found a transforming factor capable of altering phenotype.
- Avery, McCarty & MacLeod, in 1944, determined that the transforming factor is DNA.
- Erwin Chargaff, in 1947, established Chargaff rules: A = T, C = G.
- Hershey & Chase, in 1952, confirmed that DNA is the genetic material.
- Watson & Crick, in 1953, determined the double helix structure of DNA.
- Meselson & Stahl, in 1958, discovered semi-conservative replication.
The "Central Dogma"
- Genetic information flows within a cell: DNA --> RNA --> protein.
- DNA undergoes replication.
- DNA also undergoes transcription to produce RNA.
- RNA undergoes translation to produce protein.
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