2. 1

3. 2 Who’s Responsible?  Rosalind Franklin took diffraction x-ray photographs of DNA crystals  In the 1950’s, Watson & Crick built the first model of DNA using Franklin’s x-rays  Nobel Peace Prize awarded

4. DNA-Deoxyribonucleic Acid DNA. DNA is often called the blueprint of life. In simple terms, DNA contains the instructions for making proteins within the cell. 3

5. Why do we study DNA? We study DNA for many reasons, e.g., its central importance to all life on Earth, medical benefits such as cures for diseases and better food crops. 4

6. Our genes are on our chromosomes. Chromosomes are made up of a chemical called DNA. Chromosomes and DNA 5

7. SHAPE of DNA DOUBLE HELIX -two sided -twisted -ladder 6

8. Nucleotide: 3 components 1)Deoxyribose Sugar 2)Phosphate 3)Nitrogen Base DNA is made of repeating nucleotides Nucleotide: monomer DNA: polymer DNA Structure 7

9. Cytosine C Thymine T Adenine A Guanine G The amount, the order 8 Four nitrogenous bases DNA has four different bases:

10. Pyrimidines are single ring bases. Purines are double ring bases. 9 Two Kinds of Bases in DNA

11. Two Stranded DNA Sides are called the backbone: made of alternating Phosphate and Sugar The ladder rungs: made of paired nitrogen bases. 10

12. Hydrogen Bonds The Bases connect by Hydrogen Bonds Hydrogen bonds are weak but there are millions and millions of them in a single molecule of DNA. The hydrogen bonds between the bases are shown here with dotted lines 11

13. Adenine and Thymine always join together AT Cytosine and Guanin always join together CG Pyrimidines and Purines always pair together 12

14. DNA by the Numbers Each cell has about 2 m of DNA. The average human has 75 trillion cells. The average human has enough DNA to go from the earth to the sun more than 400 times. DNA has a diameter of only 0.000000002 m. 13 The earth is 150 billion m or 93 million miles from the sun.