1. 1 DNA and Replication

2. Rosalind Franklin 2

3. 3 Chargaff’s Rule Adenine ThymineAdenine must pair with Thymine Guanine CytosineGuanine must pair with Cytosine The bases form weak hydrogen bonds G C TA

4. 4 DNA Two strands coiled called a double helix Sides made of a pentose sugar Deoxyribose bonded to phosphate (PO 4 ) groups Center made of nitrogen bases bonded together by weak hydrogen bonds

5. 5 Three Parts of the DNA Nucleotide O O=P-O OPhosphate Group Group N Nitrogenous base (A, G, C, or T) (A, G, C, or T) CH2 O C C CC Sugar Sugar(deoxyribose)

6. 6 DNA P P P O O O P P P O O O G C TA

7. Question Adenine CytosineIf there is 30% Adenine, how much Cytosine is present? 7

8. Answer CytosineThere would be 20% Cytosine Adenine (30%) = Thymine (30%)Adenine (30%) = Thymine (30%) Guanine (20%) = Cytosine (20%)Guanine (20%) = Cytosine (20%) Therefore, 60% A-T and 40% C-GTherefore, 60% A-T and 40% C-G 8

9. 9 DNA Replication

10. 10 Replication Facts DNA is copied in a cell before a cell divides by mitosis, meiosis, or binary fission.DNA is copied in a cell before a cell divides by mitosis, meiosis, or binary fission.

11. 11 DNA Replication Begins at Origins of ReplicationBegins at Origins of Replication Two strands open forming Replication Forks (Y-shaped region)Two strands open forming Replication Forks (Y-shaped region) New strands grow at the forksNew strands grow at the forks ReplicationFork Parental DNA Molecule 3’ 5’ 3’ 5’

12. 12 DNA as a Zipper

13. 13 DNA Replication Enzyme Helicase unwinds and separates the 2 DNA strands by breaking the weak hydrogen bondsEnzyme Helicase unwinds and separates the 2 DNA strands by breaking the weak hydrogen bonds

14. Question How does the structure of DNA make it easy to copy? 14

15. 15 DNA Replication DNA polymerase (enzyme) adds the new nucleotides Covalent bonds form between deoxyribose sugar and phosphate group. Hydrogen bonds between nitrogenous bases.

16. 16 Zipper Movement

17. Question Are the nucleotides of the new sequences of the new strand identical to the original? 17

18. 18 Synthesis of the New DNA Strands The Leading Strand single strandThe Leading Strand is synthesized as a single strand from the point of origin toward the opening replication fork RNAPrimer DNA Polymerase Nucleotides 3’5’

19. 19 Synthesis of the New DNA Strands The Lagging Strand isThe Lagging Strand is made in MANY short segments It is replicated from the replication fork toward the origin Leaves gaps in new strand. Gaps filled in by DNA ligase RNA Primer Leading Strand DNA Polymerase 5’5’ 5’ 3’ Lagging Strand 5’ 3’

20. 20 Replication of Strands Replication Fork Point of Origin

21. 21 Semiconservative Model of Replication New DNA consists of 1 PARENTAL ( template ) and 1 NEW ( complementary) strand of DNA Parental DNA DNA Template New DNA

22. Question Why is the new strand complementary to the original strand? 22

23. Question After a cell’s DNA is replicated, the cell may divide in two. Each new cell receives one copy of the original cell’s DNA. How are the new strands and the original strands divided between the two new cells? 23

24. 24 Explain the statement, “DNA replication depends on specific base pairs”.

25. 25 Activity: Is photography a document similar to DNA replication? Think of the original materials, the copying process, and the final products. Explain how the two processes are alike. Identify major differences.