1. History and Structure of DNA Part Two

2. DNA-Common Genetic Code After it was proven that DNA was the material of genes, studies began to learn about the structure, processes, and control mechanisms of DNA.

3. DNA Remember back to our studies of the macromolecules. DNA is a long polymer of nucleic acids. A nucleic acid is made of a sugar ring, a phosphate group, and a nitrogenous base. The sugar and phosphate bond to form the “backbone” of a DNA strand. There are 4 nitrogenous bases: Adenine, Cytosine, Thymine, and Guanine.

4. Chargaff 1930 American Biologist Credited with “Chargaff’s Rules” –The amount of A will equal the amount of T in any DNA; and, the amount of G will equal the amount of C in any DNA. –Each species on Earth has a unique percentage of the bases A, T, G, and C.

5. Chargaff’s Rules Chargaff determined that globally, A=T and C=G. The ratios tend to remain constant within a species but different between species.

6. Franklin 1950 British Scientist Took an “X-ray” of DNA. Showed that DNA was helical (spiral).

7. Franklin X-ray Photos

8. Watson and Crick 1953 British and American Using Chargaff’s Rules and Franklin’s X-ray, Watson and Crick correctly develop the double helix DNA model.

9. Watson and Crick Model

10. Homework DNA structure worksheet, coloring and questions. As long as you are using your time wisely you will have time to work on it tomorrow.