DNA stands for deoxyribose nucleic acid. This chemical substance is present in the nucleus of all cells in all living organisms

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1 DNA Structure Notes

2 DNA stands for deoxyribose nucleic acid This chemical substance is present in the nucleus of all cells in all living organisms DNA determines the kind of cell which is formed, (muscle, blood, nerve etc) is controlled by DNA DNA determines the kind of organism which is produced (buttercup,giraffe, herring, human etc) is controlled by DNA DNA is often called the blueprint of life because it contains the instructions for making proteins within the cell.

3 DNA is a very long polymer. The basic shape is like a twisted ladder or zipper. This is called a double helix. The DNA double helix has two strands twisted together.

4 DNA Structure DNA is made up of nucleotides Nucleotides Have Three Parts phosphate 1. Simple Sugar (5-carbon sugar) 2. Phosphate group 3. Nitrogen Base deoxyribose Bases or nucleotides

5 Looking at the Structure of DNA In 1953 Watson and Crick solved the puzzle (p. 292 Fig ) These two scientists viewed x-ray images of DNA crystals that were created by Rosalind Franklin and Maurice Wilkins. DNA Structure Resembles a ladder sides: sugar and phosphate rungs (steps): complementary pairs of nitrogen bases

6 In DNA, there are four possible nitrogen bases. Pyrimidines Thymine (T) Cytosine (C) Purines Adenine (A) Guanine (G) Pyrimidines are single ring bases. Purines are double ring bases. O C N N C N N C C N C N C C C N N C

7 Chargraff s Rule: The bases attract each other because of hydrogen bonds. Hydrogen bonds are weak but there are millions and millions of them in a single molecule of DNA. The bonds between are shown here with dotted lines Adenine and Thymine always join together A T Cytosine and Guanine always join together C G

8 DNA Deoxyribose nucleic acid type of nucleic acid What is the other type of nucleic acid? RNA DNA function to hold genetic code Genetic code = genetic instructions to make proteins DNA is found in nucleus of eukaryotic cells Found in nucleoid region in prokaryotes

9 The Short History of DNA From

10 Searching for Genetic Material Gregor Mendel (1866): discovered that inherited traits are determined by discrete units, or 'genes, - passed on from the parents. Freidrich Miescher(1868): discovered DNA Isolated something new from the nuclei of eukaryotic cells Later called DNA!!!

11 Searching for Genetic Material Thomas Hunt Morgan (1910): Worked with fruit flies Specifically eye color of these flies! Discovered genes are located (linked) on chromosomes (Like x-linked traits)

12 Staining of DNA reveals somatic cells have the same amount 1914-Robert of DNA and Feulgen half as much as gametes. A German chemist, found a staining technique that stains more or less strongly based in the amount of DNA present (called Feulgen stain). He found that all cells in an organism had the same amount of DNA (46) except gametes, which had half the normal amount. Cells stained with Feulgen stain. It is the DNA and not the proteins that are visible under the microscope.

13 Fredrick Griffith (1928): Studied effects of virulent (harmful) bacteria vs. nonvirulent bacteria injected into mice Used transformation: Inserted foreign DNA and changed protein/ trait Believed that the transforming agent was an inheritance molecule. ROUGH: harmless Nonvirulent vs. Virulent Bacteria SMOOTH: kill

14 NOT HARMFUL / BENIGN BAD / HARMFUL

15 Griffith's Transformation Experiment Used the Pneumococcus bacteria When heated Smooth (harmful) cells (DEAD) are mixed with living Rough (benign) cells and injected into mice, the mouse dies. WHY?

16 Oswald Avery, Colin MacLeod, & Maclyn McCarty (1944): Reported that transforming agent in Griffith's experiment was DNA. Also used the Pneumococcus bacteria and test tubes (NOT mice) When various isolated chemical components of the S-strain Pneumococcus cells was mixed the R-strain Pneumococcus cells, it was shown that the DNA from the S-strain cells, that caused trans-formation.

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18 Edwin Chargaff (1950) Discovered a 1:1 ratio of adenine to thymine and guanine to cytosine in DNA samples from a variety of organisms. Relative Proportions (%) of Bases in DNA ORGANISM A T G C Human Chicken Grasshopper Sea Urchin Wheat Yeast E. coli Chargaff s Rules A = T C G

19 Maurice Wilkins (1952) Photographed DNA using x-ray crystallography Worked with another scientists named Rosalind Franklin Awarded the 1962 Nobel Prize for Physiology or Medicine with Watson and Crick Rosalind Franklin (1952) Photo 51 Obtained sharp X-ray diffraction photographs of DNA (Photo 51) Watson and Crick used her data revealed its helical shape Watson and Crick went on to win Nobel Prize (1962) for their DNA model

20 Linus Pauling s TRIPLE helix Linus Pauling (1954) proposed a triple helix structure for DNA Pauling Triple Helix Model

21 How did PHOTO 51 reveal DNA s helical shape?

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23 X-rays passing through a helix diffract at angles perpendicular to helix making an "X" pattern, which favors an equal diameter "helix".

24 She finally gets credit Rosalind Franklin University of Medicine and Science, located on Green Bay Road in North Chicago, Illinois

25 Alfred Hershey & Martha Chase (1952) Confirmed DNA was genetic material using viruses that infect bacteria. These viruses only stay on the outside of the cell when infecting the cells. Also viruses are composed of protein and DNA. It is known that the virus injects its genetic material into the bacterium which had to DNA or proteins. Used bacteriophages (viruses) HYPOTHESIZED DNA, not protein, is the hereditary material

26 Searching for Genetic Material Hershey and Chase Experiment Animation nimations.html

27 Experiment of Hershey and Chase 27

28 Discovering the structure of DNA James Watson & Francis Crick (1953) 1. Determined that the sugar and phosphates were on the outside. 2. Determined that the nitrogenous bases were forming the rungs of the ladder.

29 Based on the work Franklin s x-ray crystallography, Watson and Crick found the bonding; two purines are too wide and would overlap. two pyrimidines are too far apart to form the hydrogen bonds. a purine and a pyrimidine however, are just right! 29

30 Chargaff s Snub Chargaff felt there had been an injustice done when he did not receive the Nobel Prize in 1962 along with Watson, Crick and Wilkins. Wilkins contribution to the structure of DNA was to show James Watson the work of Rosalind Franklin without her permission. Franklin did not share the Nobel Prize as she passed away from ovarian cancer in 1958 and posthumous nominations are forbidden. 30

31 Sides of the Ladder 31

32 Hydrogen Bonding and Nitrogenous Bases 32

33 Hydrogen Bonding and Nitrogenous Bases 33

34 Hydrogen Bonding and Nitrogenous Bases 34

35 Hydrogen Bonding and Nitrogenous Bases 35

36 Forming the Double Helix 36