1. DNA and Replication

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

3. DNA Structure Review

4. DNA Double Helix Phosphate & Sugar Backbone “Legs of ladder” Nitrogenous Base (A,T,G or C) “Rungs of ladder”

5. DNA Stands for Deoxyribonucleic acid nucleotidesMade up of subunits called nucleotides Nucleotide made of:Nucleotide made of: Phosphate group 1.Phosphate group 5-carbon sugar 2.5-carbon sugar Nitrogenous base 3.Nitrogenous base

6. DNA Nucleotide CH2 O C1C1 C4C4 C3C3 C2C2 5 Sugar Sugar(deoxyribose) N Nitrogenous base (A, G, C, or T) (A, G, C, or T) O O=P-O OPhosphate Group Group

7. P P P O O O 1 2 3 4 5 5 3 3 5 P P P O O O 1 2 3 4 5 5 3 5 3 G C TA DNA

8. Nitrogenous Bases Double ring PURINES Adenine (A) Guanine (G) Single ring PYRIMIDINES Thymine (T) Cytosine (C) A or G T or C

9. Base-Pairings Purines only pair with Pyrimidines Three hydrogen bonds required to bond Guanine & Cytosine CG 3 H-bonds

10. Two hydrogen bonds are required to bond Adenine & Thymine T A

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

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

13. What ensures that future copies of DNA are identical to the original DNA molecule sequence?

14. DNA Replication <>

15. Replication Facts DNA has to be copied before a cell dividesDNA has to be copied before a cell divides DNA is copied during the S or synthesis phase of interphaseDNA is copied during the S or synthesis phase of interphase New cells will need identical DNA strandsNew cells will need identical DNA strands

16. Synthesis Phase (S phase) S phase during interphase of the cell cycle Nucleus of eukaryotes Mitosis -prophase -metaphase -anaphase -telophase G1G1 G2G2 S phase interphase DNA replication takes place in the S phase.

17. DNA Replication As the 2 DNA strands open at the origin, Replication Bubbles formAs the 2 DNA strands open at the origin, Replication Bubbles form Eukaryotic chromosomes have MANY bubbles Prokaryotes (bacteria) have a single bubble Bubbles

18. 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

20. DNA Replication DNA polymerase can only add nucleotides to the 3’ end of the DNA This causes the NEW strand to be built in a 5’ to 3’ direction RNAPrimer DNA Polymerase Nucleotide 5’ 3’ Direction of Replication

21. Remember the Strands are Antiparallel P P P O O O 1 2 3 4 5 5 3 3 5 P P P O O O 1 2 3 4 5 5 3 5 3 G C TA

22. So, what ensures that future copies of DNA are identical to the original DNA molecule sequence?

23. Complimentary base pairing- A = T and C = G

24. Question: What would be the complementary DNA strand for the following DNA sequence? DNA 5’-GCGTATG-3’

25. Answer: DNA 3’-CGCATAC-5’