1. DNA: Deoxyribonucleic Acid Biology

2. Structure of DNA DNA nucleotide has 3 parts: Sugar molecule Deoxyribose Phosphate group Nitrogen-containing base DNA nucleotide has 3 parts: Sugar molecule Deoxyribose Phosphate group Nitrogen-containing base

3. Nitrogen-containing bases Adenine = A Guanine = G Cytosine = C Thymine = T

4. Nucleotide Structure Purines Bases that have two rings of carbon and nitrogen atoms Adenine and guanine Purines Bases that have two rings of carbon and nitrogen atoms Adenine and guanine

5. Nucleotide Structure Pyrimidines Bases that have only one ring of carbon and nitrogen atoms Cytosine and thymine

6. The Origin of the Double Helix Rosalind Franklin X-ray photographs of DNA crystals Research partner Maurice Wilkins

7. The Origin of the Double Helix Watson & Crick Used Franklin’s stolen research and photographs to determine the structure of DNA 1953 Watson & Crick Used Franklin’s stolen research and photographs to determine the structure of DNA 1953

8. The Double Helix DNA is composed of two nucleotide chains that wrap around each other to form a double spiral, like a spiral staircase Double helix DNA is composed of two nucleotide chains that wrap around each other to form a double spiral, like a spiral staircase Double helix

9. The Double Helix The “backbone” of the double helix Alternating sugar and phosphate molecules Nitrogen-containing bases attach to the sugar molecules in the “backbone” and occupy the space in the center

10. Complementary Base Pairing DNA nucleotides pair in specific combinations Base-pairing rules Cytosine & Guanine C - G Adenine & Thymine A - T

11. Complementary Base Pairing The complementary base pairs are a combination Purine with a pyrimidine Two rings paired with a single ring The complementary base pairs are a combination Purine with a pyrimidine Two rings paired with a single ring

12. Complementary Base Pairing Base pairs are connected to one another by hydrogen bonds

13. Replication of DNA Replication The process of copying DNA in the cell Replication The process of copying DNA in the cell

14. Replication of DNA-Step 1 The separation of the two nucleotide strands The point at which the two chains separate Replication fork

15. Replication of DNA-Step 1 The nucleotide chains are separated by enzymes Helicases Run down the strand and break the bonds holding the complemen- tary bases together The nucleotide chains are separated by enzymes Helicases Run down the strand and break the bonds holding the complemen- tary bases together

16. Replication of DNA-Step 2 DNA polymerase binds to the separated chains of DNA Runs along the separated strands

17. Replication of DNA-Step 2 New chains of DNA are assembled using nucleotides in the surrounding medium that are complementary to the existing DNA chains

18. Replication of DNA-Step 3 Once the DNA is copied the cell is ready to undergo cell division

19. Accuracy and Repair Replication is very accurate One error in every 10,000 pairs of nucleotides Mutations do occur A mistake that results in a change in the nucleotide sequence Replication is very accurate One error in every 10,000 pairs of nucleotides Mutations do occur A mistake that results in a change in the nucleotide sequence

20. Accuracy and Repair The number of errors and mutations are reduced by proofreading enzymes They detect errors and replace the wrong nucleotide with the correct nucleotide Doesn’t always work Skin cancer