DNA Structure and Classic experiments, excerpt 1 | MIT 7.01SC Fundamentals of Biology
MIT OpenCourseWare・2 minutes read
Mutants affecting biochemistry were linked to genetic function in a study connecting genetics and biochemistry through purification of hereditary material. DNA was identified as the transforming substance in a series of experiments, leading to the revelation of the double helix structure by Watson, Crick, and Franklin.
Insights
- Griffiths' discovery of the transforming principle in 1928, through experiments with virulent and non-virulent bacteria, laid the foundation for identifying DNA as the key substance responsible for genetic transformation, marking a pivotal moment in understanding the link between genetics and biochemistry.
- The elucidation of the double helix structure of DNA by Watson, Crick, and Franklin, coupled with Chargaff's rules and the concept of semi-conservative replication demonstrated by Meselson and Stahl, revolutionized our comprehension of heredity and mutation, unveiling the fundamental role of DNA as a template for replication and providing a framework for understanding genetic inheritance and variability.
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Recent questions
What substance did Avery, McCarty, and MacLeod identify as the transforming principle?
DNA
What did Hershey and Chase's experiment in the 1950s focus on?
Viral infections in bacteria
Who deduced the helical structure of DNA with Rosalind Franklin's data?
James Watson and Francis Crick
What did Meselson and Stahl demonstrate through their experiment using isotopic labeling?
Semi-conservative replication
What was the significance of the double helix structure in heredity?
Template for replication and mutation
Related videos
Summary
00:00
"DNA's Role in Biochemistry and Genetics"
- Mutants were found that affect biochemistry, linking function and gene.
- To connect genetics and biochemistry, heredity needs to be purified in a test tube.
- Griffiths in 1928 discovered the transforming principle, a substance, not an idea.
- Griffiths studied pneumococcus due to the Spanish influenza epidemic.
- Griffiths experimented with smooth, virulent and rough, non-virulent bacteria on mice.
- Heat-killed virulent bacteria transformed harmless bacteria into virulence.
- Avery, McCarty, and MacLeod in 1943 identified DNA as the transforming substance.
- Skepticism arose due to DNA being considered a boring molecule.
- DNA structure includes 2 prime deoxyribose sugar, nitrogenous bases (A, G, T, C), and triphosphate for energy.
- Polymerization of DNA involves linking bases, sugars, and phosphates.
18:35
"DNA Structure, Bases, and Transforming Principle"
- DNA structure involves sugar and phosphate repeating units, with 5-prime and 3-prime attachments.
- Bases in DNA are purines (A and G) with a six-membered and five-membered ring structure, and pyrimidines (T and C) with a six-membered ring.
- Bases in DNA have similar chemical properties, unlike amino acids with diverse properties.
- Avery, McCarty, and MacLeod's DNA transforming principle was initially unimpressive.
- Hershey and Chase's experiment in the 1950s focused on viral infections in bacteria.
- Bacterial viruses consist of a protein coat and DNA inside, with limited components.
- Hershey and Chase used P-32 for DNA labeling and S-35 for protein labeling in their experiment.
- The Waring blender was used to separate virus particles from bacteria in the experiment.
- DNA was found to be the transforming principle in the Hershey-Chase experiment.
- James Watson and Francis Crick, with Rosalind Franklin's data, deduced the helical structure of DNA.
34:39
"Discovery of DNA Double Helix Structure"
- The Double Helix, the Structure of DNA, was published in April of 1953, revealing the iconic double helix structure with two anti-parallel strands running in 5 prime to 3 prime directions.
- Base pairing between purines and pyrimidines was highlighted, with T pairing with A through two hydrogen bonds, and C pairing with G through three hydrogen bonds.
- Chargaff's rules were introduced, emphasizing the equal ratios of A to T and G to C in DNA, discovered by chemist Erwin Chargaff.
- Crick and Watson's discovery of the double helix structure was celebrated in February 1953, leading to their publication in Nature in April of the same year.
- The significance of the double helix lay in its role in heredity, with each strand serving as a template for replication, explaining the process of mutation.
- Crick and Watson hinted at the implications of their discovery in heredity and mutation, promising to address it further in subsequent papers.
- Proof of semi-conservative replication was demonstrated by Meselson and Stahl through an experiment using isotopic labeling to show that each new DNA strand contained one old and one new strand, validating the Crick-Watson model.
