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History of DNA structure and its importance How did we learn that DNA is the key to coding for all characteristics of living things?

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Presentation on theme: "History of DNA structure and its importance How did we learn that DNA is the key to coding for all characteristics of living things?"— Presentation transcript:

1 History of DNA structure and its importance How did we learn that DNA is the key to coding for all characteristics of living things?

2 A timeline… 1869: *Friedrich Miescher – Swiss researcher *isolated a new molecule – “nuclein” - from the cell nucleus *determined that nuclein was made up of H, O, N, and P *there was a unique ratio of P to N 1928: *British scientist -- Frederick Griffith studies bacteria looking for cause of pneumonia *found two specific strains or cultures of bacteria that looked different when growing on petri dishes: -one grew in smooth-edged groups -other one produced colonies that were rough and ragged around the edges

3 Why Griffith’s study important? Visual differences made it easy to recognize and distinguish between the strains of bacteria Also, Griffith found that: *smooth-edged colonies of bacteria caused disease *rough-edged colonies were harmless

4 Disease-causing bacteria (smooth colonies) Harmless bacteria (rough colonies) Heat-killed, disease- causing bacteria (smooth colonies) Control (no growth) Heat-killed, disease-causing bacteria (smooth colonies) Harmless bacteria (rough colonies) Dies of pneumoniaLives Live, disease-causing bacteria (smooth colonies) Dies of pneumonia Section 12-1 Griffith’s Experiment Go to Section:

5 Disease-causing bacteria (smooth colonies) Harmless bacteria (rough colonies) Heat-killed, disease- causing bacteria (smooth colonies) Control (no growth) Heat-killed, disease-causing bacteria (smooth colonies) Harmless bacteria (rough colonies) Dies of pneumoniaLives Live, disease-causing bacteria (smooth colonies) Dies of pneumonia Section 12-1 Griffith’s Experiment Go to Section:

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7 Results of Griffith’s 1928 experiment: Discovery of process of Transformation Somehow the heat-killed bacteria had passed their disease-causing ability to the harmless strain The harmless strain had been “transformed” into a disease-causing strain Griffith hypothesized that some “factor” was responsible for this change…

8 Timeline con’t 1944: -American, Oswald Avery, continued bacteria research of Griffith -Knew were 4 types of organic compounds that make up all life… - in multiple experiments, he used enzymes to destroy lipids, carbohydrates, proteins, and RNA in an extract from the disease causing bacteria – that left only DNA!

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10 Transformation still occurred, so obviously the molecules they had destroyed were not responsible for transformation. Only organic molecule left that had not been destroyed was DNA When repeated experiment with DNA- destroying enzymes, no transformation occurred….DNA was the key to heredity

11 Timeline con’t 1952: -Americans Alfred Hershey and Martha Chase -worked with viruses called bacteriophages -viruses are simple – DNA or RNA core and a protein coat around them -when infect, bacteriophages inject DNA or RNA into cell and protein coat is left outside -used radioactive markers to trace – phosphorus-32 ( 32 P) for DNA sulfur-35 ( 35 S) for protein coat

12 Figure 16.2a The Hershey-Chase experiment: phages

13 Bacteriophage with phosphorus-32 in DNA Phage infects bacterium Radioactivity inside bacterium Bacteriophage with sulfur-35 in protein coat Phage infects bacterium No radioactivity inside bacterium Hershey-Chase Experiment Section 12-1 Go to Section:

14 Results of Hershey-Chase… When viruses were separated from the bacteria and tested for radioactivity, all of the radioactivity from the bacteria was found to be 32P – Conclusion: genetic material of the bacteriophage that was transferred was DNA

15 Race for the structure of DNA… ~1940: - Erwin Chargaff discovers that percentages of A and T are equal in any sample of DNA; same is true for C and G 1944: - Linus Pauling discovers that proteins can have a helical shape 1952: - Rosalind Franklin takes pictures of DNA molecule using technique called X-ray diffraction, shows that DNA has helical shape

16 Figure 16.4 Rosalind Franklin and her X-ray diffraction photo of DNA

17 : - Maurice Wilkins works with X- ray diffraction and sees same pattern as Franklin, shares info with James Watson April, 1953: - James Watson and Francis Crick build first model of DNA (are awarded Nobel Prize in 1960’s)

18 Figure 5.x3 James Watson and Francis Crick

19 Watson presents on the discovery of the structure of DNA…Watson presents on the discovery Cold Spring Harbor, New York (CNN) -- At 85, James Watson still plays tennis every week. His hips and knees haven't given out yet, he says, and he likes grass courts. CNN interview

20 Scientist review… Researched ID of DNA as genetic material: Miescher Griffith Avery Hershey and Chase Researched info on structure/function of DNA: Chargaff Pauling Franklin Wilkins Watson and Crick

21 Building blocks of nucleic acids are nucleotides *phosphate group, pentose sugar, and a nitrogenous base (A,T,C,G,U) DNA – bases are A,T,C,G RNA – bases are A,U,C,G

22 Figure 5.29 The components of nucleic acids Figure 5.29 The components of nucleic acids

23 Figure 16.6 Base pairing in DNA

24 Unnumbered Figure (page 292) Purine and pyridimine Why does A always pair with T (or U), and G with C?

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26 Chromosome Structure of Eukaryotes Chromosome Supercoils Coils Nucleosome Histones DNA double helix Section 12-2 Go to Section:

27 3 Important Gene Functions 1. Carry information from one generation to the next. 2. Put that information to work by determining the heritable characteristics of organisms. 3. Have to be easily copied each time a cell divides.


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