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DNA

DNA. A. The Genetic Code – the way cells store info and pass it on to other cells 1. Stored in… DNA …how do we know?. 2. Frederick Griffith – studying how certain bacteria cause pneumonia a. Two strains i. Smooth – has a protective capsule  c auses pneumonia

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DNA

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  1. DNA

  2. A. The Genetic Code – the way cells store info and pass it on to other cells 1. Stored in…DNA…how do we know?

  3. 2. Frederick Griffith – studying how certain bacteria cause pneumonia a. Two strains i. Smooth – has a protective capsule  causes pneumonia ii. Rough – no capsule  does not cause pneumonia b. Does the capsule cause pneumonia? i. Heat-killed the smooth bacteria ii. Rats did not develop pneumonia iii. Capsule does not cause pneumonia

  4. c. Combine rough & heat-killed smooth  rats die of pneumonia i. The rough strain had acquired capsules ii. They (the bacteria) could protect themselves from the rat’s immune system d. This means that the ability to cause the disease was transferred from the heat-killed smooth to the rough (DNA was transferred from smooth to rough) e. Griffith called this process transformation

  5. Griffith’s Transformation Experiments

  6. 3. Oswald Avery – which molecule contains the genetic code? a. Created an extract from smooth bacteria b. Treated the extract with enzymes that destroy lipids, carbs, proteins, RNA & DNA (one at a time) c. Extract continued to cause the disease except when the DNA-destroying enzyme was used d. What did this mean? DNA carries the genetic code

  7. 4. Hershey & Chase a. Bacteriophage – a virus that infects bacteria (uses the bacteria to make more viruses) b. How does the virus “reprogram” the bacterium? Does it use DNA or proteins? c. Labeled viral DNA with radioactive phosphorus; labeled viral protein coat with radioactive sulfur

  8. d. The labeled bacteriophages were allowed to infect E. coli bacteria e. Remove bacteriophages (viruses) f. Test for radioactivity i. Radioactive phosphorus (DNA) was found inside the E. coli bacteria (because it does the reprogramming) ii. Radioactive sulfur (protein) remained with the bacteriophages (Proved again that DNA is the genetic material)

  9. Hershey & Chase Experiment

  10. B. Structure of DNA 1. DNA is a polymer; what is the monomer? Nucleotide 2. Made up of three parts a. Sugar (Deoxyribose) b. Phosphate group

  11. c. Base (1 of 4 possibilities) i. Adenine (A) iii. Cytosine (C) ii. Guanine (G) iv. Thymine (T) * Edwin Chargaff found that in each organism, the amount of A = T and the amount of C = G (Became known as Chargaff’s rules)

  12. 3. How was the structure of DNA discovered? a. Rosalind Franklin & Maurice Wilkins i. Took x-ray pictures of DNA ii. Franklin’s Findings – DNA is spiral, probably has two strands & has large groups spaced out in regular intervals iii. Wilkins shared Franklin’s data with Watson & Crick without Franklin’s permission

  13. Rosalind Franklin’s Photo 51

  14. b. James Watson & Francis Crick i. used clues from Chargaff & Franklin ii. Put a model of DNA together using trial and error iii. Won a Nobel Prize in 1962 (along with Maurice Wilkins) *Franklin died four years earlier, so she was not eligible for the award. No mention was made of Franklin at the time of the award.

  15. 4. The Double Helix – two strands twisted around each other in a spiral a. Sugars and phosphates form the backbone of DNA b. The bases connect the two DNA strands together c. The bases connect to each other by forming hydrogen bonds

  16. d. Base pairing (Chargaff) – the attraction between two bases i. Adenine and Thymine always match up (A-T) ii. Cytosine and Guanine always match up (C-G)

  17. C. DNA Replication 1. Strands are complementary a. The sequence of one strand determines the sequence of the other b. A basis for exact copies 2. Before a cell divides it must copy its DNA – replication 3. Why is replication necessary? So each new cell gets a complete set of genetic information

  18. 4. Steps of DNA Replication a. Unwind & unzip the DNA strands i. Enzyme – DNA helicase ii. Other enzymes hold the two strands apart  replication fork b. Free nucleotides come in and match up by base pairing to make a new strand i. Enzyme – DNA polymerase

  19. c. DNA polymerase also proofreads i. Looks at the order of the bases and checks for mistakes ii. Will fix mistakes if they are found d. Result? Two complete, identical DNA molecules (each with two strands)

  20. 5. Rate of DNA Replication a. DNA strands are very long  usually replication is happening in many locations all at once b. One chromosome can be replicated in about 8 hours (for humans)

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