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The Culmination of DNA Discoveries: Unraveling its Genetic Essence

Explore the historical journey to uncover DNA as the primary genetic material, from Griffith's experiments to Hershey-Chase's viral discoveries. Dive into the pivotal research of Avery, McCarty, and MacLeod that solidified DNA's importance, leading to Watson and Crick's breakthrough double helix model. Understand the fundamental structure of DNA nucleotides, nitrogenous bases, and the crucial base-pairing rules shaping genetics.

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The Culmination of DNA Discoveries: Unraveling its Genetic Essence

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  1. The History and Structure of DNA(Chapter 13)

  2. DNA:___________________ • _________ are made up of small segments on a chromosome (made of deoxyribonucleic acid or “DNA”) • DNA is the primary material that causes recognizable, inheritable characteristics in related groups of organisms.

  3. Searching for the Genetic Material 3 major _______________________ ________________________________________________________

  4. 1. - 1928 • Worked with 2 types of bacteria in mice (S bacteria & R bacteria) • Discovered “transformation” – the transfer of genetic material in the form of DNA fragments from one cell to another.

  5. Conclusion of Griffith’s Experiment: • Something is present in the Smooth bacteria that is capable of transforming the Rough into Smooth • This “mystery substance” is _________ _________________________________ Hmmm…what could this mystery substance be?

  6. 2. Avery, McCarty & MacLeod • 1944—Wanted to determine whether the transforming agent in Griffith’s experiments was a_________________ _________________________________ • Used enzymes to destroy each of these molecules in the Smooth (disease-causing) bacteria.

  7. Avery, McCarty & MacLeod’s Experiment, Step by Step: • Step 1: Using enzymes, they took the heat-killed smooth bacteria and removed the carbohydrates. After adding this to the Live Rough bacteria, they injected mice. • The mice died of pneumonia. This means the Live Rough still turned into Smooth.

  8. Avery, McCarty & MacLeod’s Experiment, Step by Step: • Step 2: This time, they used enzymes to destroy the lipids in the heat-killed smooth. After adding it to the Live Rough, they injected mice. • The mice died of pneumonia. This means the Live Rough still turned into Smooth, even without the lipids.

  9. Avery, McCarty & MacLeod’s Experiment, Step by Step: • Step 3: This time, they used enzymes to destroy the proteins in the heat-killed smooth. After adding it to the Live Rough, they injected mice. • The mice died of pneumonia. This means the Live Rough still turned into Smooth, even without the proteins.

  10. Avery, McCarty & MacLeod’s Experiment, Step by Step: • Step 4: This time, they used enzymes to destroy the DNA in the heat-killed smooth. After adding it to the Live Rough, they injected mice. • The mice lived! This means the Live Rough stayed Rough! Without the DNA from the smooth, the Rough did not turn into smooth.

  11. Conclusion of Avery’s Experiment: • ________________________________ _________________________________ Were their findings accepted by the scientific community?

  12. 3. Alfred Hershey & Martha Chase - 1952 • Worked with bacteriophages (infectious viruses) made up of proteins and DNA. • Found that DNA is the hereditary material in viruses.

  13. Life Cycle of a Virus Thanks to the Hershey-Chase Experiment, we now know what part of the virus is injected into the cell.

  14. Hershey-Chase Experiment:

  15. Conclusion of the Hershey/Chase Experiment: • ________________________________ _________________________________

  16. The Race is On…… • In the 1950s, we knew genes were made of DNA but knew nothing about its ___________. • Scientists around the world were actively searching for more information about DNA

  17. ___________________________ • Received his doctoral degree at age 22 in Zoology, with an emphasis on genetics. He also did post-doctoral research in biochemistry. • Francis Crick, 36, a physicist working at Cambridge University in England James Watson Francis Crick

  18. James Watson & Francis Crick • ____________________________________ _____________________________________ • The chains are twisted around a central axis and are held together by weak ___________________.

  19. How did Watson & Crick determine this structure?(3 contributions) 1. In 1949, Erwin Chargaff found that there was always the same percent of ____________________and the same percent of _______________________. This is known as ___________________

  20. 2. In 1952, Rosalind Franklin & Maurice Wilkins developed high quality ______ ____________________ Images resembled a tightly coiled helix of 2 chains.

  21. 3. In 1953, Watson & Crick used the findings of _____________________to create a 3-D _______________.

  22. DNA Nucleotide Subunits:phosphate/sugar backbone with nucleotide bases

  23. The 4 Nitrogen Bases:

  24. Nitrogenous Bases • _________– Have 2 rings of carbon & nitrogen atoms per base. A – ___________ G – ___________ • _____________– Have 1 ring of C & N atom per base T – ____________ C – ____________

  25. Base- Pairing Rules • A purine on one strand of DNA is always paired with a pyrimidine on the other • _____________ • _____________

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