2. 1

3. 2 DNA DNA.DNA is the blueprint of life. DNA contains the instructions for making proteins

4. 3 Watson & Crick’s Model

5. 4 DNA Why do we study DNA? all life on Earth depends on DNA to pass on genetic traits and run cells medical benefits such as cures for diseases, better food crops.

6. 5 Chromosomes and DNA genes are on chromosomes. Chromosomes are made of DNA.

7. 6 The Shape of the Molecule DNA is a very long polymer. Basic shape is a twisted ladder called a double helix.

8. 7 The Double Helix Molecule The DNA double helix has two strands twisted together.

9. 8 One Strand of DNA The backbone of DNA is alternating phosphates and deoxyribose sugar The teeth are nitrogenous bases. phosphate deoxyribose bases

10. 9 Nucleotides CC C O Phosphate O C C O -P O O O O O O O One deoxyribose plus phosphate and base make a nucleotide. Nitrogenous base Deoxyribose

11. 10 Four nitrogenous bases Cytosine C Thymine T Adenine A Guanine G DNA has four different bases:

12. 11 Two Kinds of Bases in DNA Pyrimidines are single ring bases.Pyrimidines are single ring bases. Purines are double ring bases.Purines are double ring bases. C C C C N N O N C C C C N N N N N C

13. 12 Thymine and Cytosine are pyrimidines and have one ring only C C C C N N O N cytosine C C C C N N O O thymine C

14. 13 Adenine and Guanine are purines and have two rings C C C C N N N Adenine N N C C C C C N N O N Guanine N N C

15. 14 Two Stranded DNA The 2 DNA fit together like a zipper. Why do the bases stick together? Hydrogen bonds!

16. 15 C C C C N N O N C C C C N N O N N N C Hydrogen Bonds Bases are attracted to each other by hydrogen bonds. Hydrogen bonds are weak attractive forces between a hydrogen on one strand and a nitrogen or oxygen on the other strand of DNA.

17. 16 Hydrogen Bonds, Hydrogen Bonds, cont. Cytosine pairs with guanine using 3 H bonds Adenine pairs with thymine using 2 H bonds C C C C N N N N N C C C C C N N O O C

18. 17 Chargraff’s Rule: Adenine with Thymine A T Cytosine with Guanine C G

19. 18 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. The earth is 150 billion m or 93 million miles from the sun.