1. DNA Structure and Repair Chapter 13 (pgs. 251-258)

2. Mutations in the DNA Sequence can also lead to diseases… Germ-line cell: cells that become egg or sperm…passed on from one generation to the next generation Ex. Huntington disease Somatic cell: cells in the body that are not egg or sperm Ex. Skin cancer

3. Environmental factors: Cigarette smoke, ultraviolet light from the sun, etc.. Breaks DNA Links adjacent T- bases together If the cell can not repair the damage, then the cell has a permanent change in its base sequence…. continued cell growth

4. 25 million cells dividing each second! Surprisingly, very few mistakes happening…. When a cell becomes damaged, we have enzymes that can repair the damage

5. The nucleus contains long strands of DNA, which holds all the information to make and control every cell

6. 1951 Watson hears a talk by Rosalind Franklin DNA X-ray crystallographs

7. Rosalind Franklin Gave a talk on her DNA photographs Not yet suggesting a structure for DNA

8. Proposed a triple helix with bases on the outside of the molecule Sugar-phosphate backbone ran down the center Phosphate groups of each chain was bound to one another by magnesium

9. Invited Franklin to their laboratory Franklin pointed out that their three-chain molecule could not exist because any magnesium would be bound to water Franklin stated the correct amount water in DNA in her talk, but Watson had forgotten

10. Rival Linus Pauling Discovers alpha-helix In 1953 announces that he discovered the structure of DNA 3 chain helix with a sugar- phosphate backbone at the center

11. Watson and Crick examined Pauling’s model Relieved that he couldn’t be right Watson put together 2-chain molecules Put sugar-phosphate backbone in the center Sugar-phosphate backbone on the outside

12. 5’ phosphate 3’ hydroxyl Phosphate group Sugar group Nucleotide base: T= thymine A= adenine G= guanine C= cytosine

13. Hydrogen bonds

14. 5' 3' 5'

17. Each single strand can serve as a template for a new strand Enzyme Helicases cause the two strands to separate New nucleotides get added on at the 3‘ end DNA Replication

19. Each single strand can serve as a template for a new strand Enzyme Helicases cause the two strands to separate New nucleotides get added on at the 3‘ end Joined together by an enzyme known as DNA polymerase DNA Replication

20. DNA polymerase: DNA editing functions Removes misplaced nucleotides and replaces it with the proper nucleotide

21. Tri-nucleotide Repeat Diseases Affect the CNS Loss of motor neurons Inherited diseases Repeated CAG or CTG DNA polymerase is unable to correct the mistake

22. Some mutations may be beneficial from an evolutionary standpoint