1. Discovering DNA structure History activity

2. Erwin Chargaff Worked with numbers of chemical molecules Look at the molecules in your bag – These are VERY short DNA pieces Count up the number of Each molecule Do you see a trend? What is it?

3. Sugar – deoxyribose Phosphate – phosphate A = adenine T = thymine G = guanine C = cytosine

4. Lord Alexander Todd Structure of nucleotide sugar (deoxyribose) phosphate a base: one of each of A, C, T or G Build as many nucleotides as you can = tape together - have to see letters/words

5. James Watson and Francis Crick Used others work to solve structure of DNA

6. DNA is long and thin and has a repeating structure. - Rosalind Franklin and Maurice Wilkins

7. DNA has a backbone made of sugar and phosphate. - Alexander Todd

8. DNA is too wide to have just one backbone. - Rosalind Franklin and Maurice Wilkins

9. DNA is about [12 cm]* wide. - Rosalind Franklin (really, 20 Angstroms)

10. The backbones of DNA are on the outside of the structure; bases are on the inside. - Rosalind Franklin

11. Bases can bond to each other within the same molecule using hydrogen bonds (weak bonds). - J. M. Gullard and D. O. Jordan

12. James Watson and Francis Crick Solved true structure of DNA Try to fit your nucleotides together – make DNA So nucleotides match: Guanine (G) bonds with Cytosine (C) Thymine (T) bonds with Adenine (A)

13. DNA structure Describe it Do you see how deoxyribose and phosphate chains on outside are opposite? A-T G - C

14. DNA Structure Shape is called double helix You made a backbone – it is actually twisted around in a helix shape Rosalind Franklin discovered “double helix” by doing X-ray diffraction Can you gently twist your DNA model?