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MOLECULAR GENETICS

MOLECULAR GENETICS . UNIT 3!. Reflect on your Learning. Answer questions 1,2,and 3 on the bottom of page 204. . History of DNA. Before the 20 th Century: It was believed that proteins were the hereditary material (because they are so prevalent in the cell) Friedrich Miescher 1869

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MOLECULAR GENETICS

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  1. MOLECULAR GENETICS UNIT 3!

  2. Reflect on your Learning... • Answer questions 1,2,and 3 on the bottom of page 204.

  3. History of DNA Before the 20th Century: It was believed that proteins were the hereditary material (because they are so prevalent in the cell) Friedrich Miescher • 1869 • Used pus cells to investigate the material inside the nucleus • Called this substance nuclein.  did not behave like proteins. • Did not know this was the hereditary material.

  4. Hammerling • 1930s • Used Acetabularia, a one-celled green algae to investigate WHERE hereditary information was stored in the cell. • Reaches 5 cm in length: great to work with. • Three distinct parts: • Foot (contains the nucleus) • Stalk • cap

  5. The hereditary information must be in the foot (and possibly the nucleus)

  6. He furthered his experiments: • Two species of Acetabularia: • A. Mediterranea: disk-shaped cap • A. Crenulata: branched, flowerlike cap. • Grafted stalk of A.c onto foot of A.m. • Subsequent cap was an intermediate between the two species: because substances that determined cap type were still in the stalk. • Excised the cap and found that the new cap formed was A. m: substances in the transplant were used up  under the control of the new nucleus. • Concluded that YES, the hereditary material is in the nucleus.

  7. The Transforming Principle • Nucleus was known to be the site of hereditary information. • Chromosomes consist of both DNA and proteins. • Which one was responsible for inheritance?

  8. Alfred D. Hershey and Martha Chase • Not until 1952 that DNA accepted as hereditary material. • Conducted experiments using a virus, bacteriophage T2: __________________. (Bacteriophages are commonly called phages) • Two components • DNA • Protein coat.

  9. How viruses work: • Attach to membrane • Inject hereditary information (PROTEIN COATS REMAIN OUTSIDE OF THE CELL) • DNA of phage takes over cell mechanics • Cell makes components (proteins and nucleic acids) of the virus • Cell assembles components into new viruses • New viruses burst out of the cell, resulting in host cell’s death • New viruses can then infect other cells.

  10. Key aspects: • Proteins contain sulfurbut no phosphorous • DNA contains phosphorus and no sulfur • Hershey and Chase tracked the location of DNA and proteins throughout infection. • Tagged some viral proteins with an isotope of sulfur, 35S • Tagged some viral DNA with an isotope of phosphorus, 32P. • Both 35S and 32P are radioisotopes: emit radiation as they decay: can be tracked. • Both types of tagged T2s were allowed to infect bacterial cells. • Cells put in blender and centrifuged to isolate bacteria parts (pellet) and viral parts (liquid)

  11. Results? • Bacterial cells infected by 35S – containing viruses did NOT contain any radioactivity. • Bacterial cells infected by 32P – containing viruses DID contain radioactivity. • THEREFORE, PHOSPHORUS-RICH DNA WAS INJECTED INTO THE BACTERIAL CELL. • This must be the genetic information.

  12. Seatwork/Homework Page 209, #2, 3, 4, 5.

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