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Questions and Answers
What primarily caused Rosalind Franklin to leave King's College?
What primarily caused Rosalind Franklin to leave King's College?
What type of research did Franklin conduct at Birkbeck College?
What type of research did Franklin conduct at Birkbeck College?
Which of the following best describes the method Franklin used in her DNA research?
Which of the following best describes the method Franklin used in her DNA research?
How did Franklin's group contribute to science?
How did Franklin's group contribute to science?
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What was the cause of Franklin's health issues later in her life?
What was the cause of Franklin's health issues later in her life?
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Which DNA replication model suggests that both parental strands remain intact after replication?
Which DNA replication model suggests that both parental strands remain intact after replication?
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What did the first replication in Meselson and Stahl's experiment produce?
What did the first replication in Meselson and Stahl's experiment produce?
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What is essential for DNA synthesis to occur in vitro?
What is essential for DNA synthesis to occur in vitro?
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Which model of DNA replication is supported by Meselson and Stahl's findings?
Which model of DNA replication is supported by Meselson and Stahl's findings?
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Why do eukaryotes require multiple origins of replication?
Why do eukaryotes require multiple origins of replication?
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What type of nitrogen isotope was used to label the parental DNA strands in the experiment?
What type of nitrogen isotope was used to label the parental DNA strands in the experiment?
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What conclusion was drawn after the second replication in Meselson and Stahl's experiment?
What conclusion was drawn after the second replication in Meselson and Stahl's experiment?
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Which statement accurately reflects a difference between eukaryotic and bacterial DNA replication?
Which statement accurately reflects a difference between eukaryotic and bacterial DNA replication?
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What occurs following the addition of acid in the DNA replication process described?
What occurs following the addition of acid in the DNA replication process described?
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In eukaryotic DNA replication, what is the result of bidirectional synthesis from multiple origins?
In eukaryotic DNA replication, what is the result of bidirectional synthesis from multiple origins?
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What significant contribution did Rosalind Franklin make to the study of DNA?
What significant contribution did Rosalind Franklin make to the study of DNA?
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What is Chargaff's rule based on?
What is Chargaff's rule based on?
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What was the early hypothesis regarding the interaction of DNA strands proposed by Watson and Crick?
What was the early hypothesis regarding the interaction of DNA strands proposed by Watson and Crick?
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What did the diffraction pattern obtained by Rosalind Franklin suggest about DNA?
What did the diffraction pattern obtained by Rosalind Franklin suggest about DNA?
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What prompted Watson and Crick's investigation into the structure of DNA?
What prompted Watson and Crick's investigation into the structure of DNA?
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What was used to trace the radioactivity in the experiment involving phages?
What was used to trace the radioactivity in the experiment involving phages?
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Which radioactive isotope was used to label the DNA in batch 2 of the phage experiment?
Which radioactive isotope was used to label the DNA in batch 2 of the phage experiment?
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What does Erwin Chargaff's findings regarding DNA suggest about its role as genetic material?
What does Erwin Chargaff's findings regarding DNA suggest about its role as genetic material?
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What was a key outcome of the centrifugation process in the phage experiments?
What was a key outcome of the centrifugation process in the phage experiments?
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Which of the following correctly states a component of a nucleotide in DNA?
Which of the following correctly states a component of a nucleotide in DNA?
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What was the significance of using both sulfur and phosphorus in the experiments?
What was the significance of using both sulfur and phosphorus in the experiments?
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What role does RNA play in some viruses, according to the information provided?
What role does RNA play in some viruses, according to the information provided?
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What does the presence of radioactive proteins in the phage shell demonstrate in the experiment?
What does the presence of radioactive proteins in the phage shell demonstrate in the experiment?
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What was the main purpose of the experiment using E. coli cultured in different nitrogen mediums?
What was the main purpose of the experiment using E. coli cultured in different nitrogen mediums?
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After the first replication in the E. coli experiment, what type of DNA was primarily observed?
After the first replication in the E. coli experiment, what type of DNA was primarily observed?
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What finding after two generations of DNA replication contradicted the dispersive model?
What finding after two generations of DNA replication contradicted the dispersive model?
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What did Arthur Kornberg hypothesize regarding DNA synthesis precursors?
What did Arthur Kornberg hypothesize regarding DNA synthesis precursors?
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Which model of DNA replication was supported after analyzing the results of the E. coli experiment?
Which model of DNA replication was supported after analyzing the results of the E. coli experiment?
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In Kornberg's experiments, why were long DNA strands not soluble in acidic solutions?
In Kornberg's experiments, why were long DNA strands not soluble in acidic solutions?
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What was the significance of using a CsCl gradient in the DNA density analysis?
What was the significance of using a CsCl gradient in the DNA density analysis?
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What did the second replication produce in the E. coli experiment that was crucial for drawing conclusions?
What did the second replication produce in the E. coli experiment that was crucial for drawing conclusions?
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Study Notes
Bio 112 Cell and Molecular Experiments
- Experiments were used to elucidate the macromolecule that carries genetic information
- Experiments were also used to discover DNA structure and how DNA is duplicated
Experiments Proving DNA is Genetic Material
- Identifying the molecules of inheritance was a challenge in the early 20th century
- The knowledge of genes being on chromosomes and their components DNA/protein meant they were considered potential candidates for genetic material
- The key to determining the genetic material was choosing appropriate experimental organisms.
- The role of DNA in heredity was first discovered through studying bacteria and viruses that infect them.
Criteria for Identifying Genetic Material
- The genetic material must contain the information to make an entire organism.
- It must be able to be transmitted from parent to offspring.
- The genetic material must be able to replicate itself.
- It must be capable of changes to account for known phenotypic variation in species.
Identification of DNA as Genetic Material: Experiments
- Griffith's experiments with Streptococcus pneumoniae (1928) showed transformation. Living R bacteria were transformed after exposure to heat-killed S bacteria, and contained the genes from the latter bacteria.
- The transforming principle was the substance causing the transformation and was determined through further experiments
- Avery, Macleod, and McCarty's experiments (1940s) concluded that DNA is the transforming principle; DNA extracted from type IIIS bacteria could convert type IIR bacteria to type IIIS. They focused only on DNA, and not other relevant macromolecules from the bacteria
- Hershey and Chase's experiment (1952) showed that DNA, not protein, is the genetic material of bacteriophages; 32P was found inside the bacterial cells after infection, while 35S was found outside.
Evidence That Viral DNA Can Program Cells
- More evidence for DNA as the genetic material came from studies of bacteriophages (viruses that infect bacteria)
- Bacteriophages are used extensively in molecular genetics research
The Structure of DNA
- After identifying DNA as the genetic material, determining its structure that accounts for its role became the next challenge
- In 1953, James Watson and Francis Crick introduced a double-helix model for DNA structure.
- Their scientific breakthrough was supported by scientists like Linus Pauling, Rosalind Franklin, Maurice Wilkins, and Erwin Chargaff
- An early hypothesis for DNA strand interaction was the phosphate-Mg++ crosslinking, which was deemed incorrect. Watson and Crick further refined the model to conform to X-ray data and determined base pairings
- Adenine always pairs with Thymine and Guanine pairs with Cytosine; This was named Chargaff's rule
- The Watson-Crick model successfully explains Chargaff’s rules
DNA Replication Experiments
- Watson and Crick's semiconservative model predicts the replication of the double helix based on pairing and one old strand being conserved per new strand
- Alternative models (conservative and dispersive) were also proposed but were later disproved by Meselson–Stahl experiment (1958). This experiment supported the semiconservative model using 15N and 14N isotopes.
In Vitro Bacterial Replication and Eukaryotic DNA Replication
- In vitro study of DNA replication was spearheaded by Arthur Kornberg in the 1950s (Nobel Prize 1959)
- Kornberg hypothesized that deoxynucleoside triphosphates are precursors for DNA synthesis.
- Eukaryotic DNA replication has similarities to bacterial replication but is more complex because of linear chromosomes and tight packaging within nucleosomes.
- Eukaryotic DNA replication originates from multiple origins of replication. This is crucial to ensure timely and complete replication. Multiple origins of replication (ARS elements) are found in eukaryotes and are similar to bacterial DNA boxes.
- A six-subunit complex called Origin Recognition Complex (ORC) plays an essential role as the initiator of eukaryotic DNA replication
- Eukaryotes contain over a dozen DNA polymerases with alpha, delta, epsilon, and gamma having the primary function
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Description
This quiz covers essential experiments that elucidate the role of DNA as the genetic material. You will explore how scientists identified DNA structure, its replication, and the criteria that classify it as genetic material. Test your understanding of the historical context and key experiments in molecular biology.
