2.  DNA contains the instructions (codes) for making all the proteins in the body.

3. 1)Hershey-Chase Experiment 2)Chargaff’s Rules 3)X-Ray Crystallography Evidence 4)Discovery of the Double Helix

4. 1952 Alfred Hershey & Martha Chase (USA)  Phage viruses only have protein & DNA; tested to see which is injected into host  Concludes DNA is the genetic material.

5. 1950 Erwin Chargaff (USA)  Discovered that the amounts of bases A & T (adenine & thymine) were roughly equal, as were amounts of C & G (cytosine & guanine).  Also found amounts of bases varied in species.

6. 1950 ’s Maurice Wilkins & Rosalind Franklin (UK)  Used X-rays to get images of molecular structures in 3D  Photograph 51 (Franklin) evidence that DNA has helical structure

7. 1953: James Watson (USA) & Francis Crick (UK)  Used models to propose structure of DNA.  Heavily influenced by fellow scientists. Concluded that DNA must be a double helix, bases paired A-T & G-C, and the strands must be anti- parallel to keep shape.

8.  DNA is a nucleic acid; a very long polymer.  Monomer unit is a nucleotide.  DNA shape is like a twisted ladder/zipper.  A.K.A. Double Helix

9. Cytosine C Thymine T Adenine A Guanine G DNA has four different bases:

10. One deoxyribose sugar together with a phosphate group and a nitrogenous base CC C O Phosphate O C C O -P O O O O O O O Nitrogenous base Deoxyribose

11. The backbone of a single DNA strand is alternating phosphates and 5- carbon sugar (deoxyribose ) The rungs/teeth are nitrogenous bases. phosphate deoxyribose bases nucleotide

12.  DNA has two strands that fit together something like a ladder/zipper.  The strands are anti-parallel  The rungs/teeth are nitrogenous bases

13.  Thymine and cytosine each have one ring of carbon and nitrogen atoms. C C C C N N O N cytosine C C C C N N O O thymine C

14.  Adenine and guanine each have two rings of carbon and nitrogen atoms. C C C C N N N Adenine N N C C C C C N N O N Guanine N N C

15.  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. C C C C N N O N C C C C N N O N N N C

16. Each cell has about 2 m of DNA. The average human has 75 trillion cells. The earth is 150 billion m from the sun The average human has enough DNA to go from the earth to the sun more than 400 times!