2. 1

3. 2 DNA DNA.DNA is often called the blueprint of life. In simple terms, DNA contains the instructions for making proteins within the cell.

4. 3 DNA Why do we study DNA? We study DNA for many reasons, e.g., its central importance to all life on Earth, medical benefits such as cures for diseases, better food crops.

5. 4 Chromosomes and DNA Our genes are on our chromosomes. Chromosomes are made up of a chemical called DNA.

6. 5 The Shape of the Molecule DNA is a very long polymer. The basic shape is like a twisted ladder or zipper. This is called a double helix.

7. 6 The Double Helix Molecule The DNA double helix has two strands twisted together.

8. 7 DNA, more??? YES!

9. 8 History of DNA

10. 9 Chromosomes are made of both DNA and protein Experiments on bacteriophage viruses by Hershey & Chase proved that DNA was the cell’s genetic material Radioactive 32 P was injected into bacteria!

11. 10 Chargaff’s Rule Adenine ThymineAdenine must pair with Thymine Guanine CytosineGuanine must pair with Cytosine The bases form weak hydrogen bonds G C TA

12. 11 DNA Structure Rosalind Franklin took diffraction x-ray photographs of DNA crystals In the 1950’s, Watson & Crick built the first model of DNA using Franklin’s x-rays

13. 12 Rosalind Franklin

14. 13 DNA Structure

15. 14 DNA Two strands coiled called a double helix Sides made of a pentose sugar Deoxyribose bonded to phosphate (PO 4 ) groups by hydrogen bonds Center made of nitrogen bases bonded together by weak hydrogen bonds

16. 15 DNA Double Helix Nitrogenous Base (A,T,G or C) “Rungs of ladder” “Legs of ladder” Phosphate & Sugar Backbone

17. 16 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

18. 17 DNA Nucleotide O O=P-O OPhosphate Group Group N Nitrogenous base (A, G, C, or T) (A, G, C, or T) CH2 O C1C1 C4C4 C3C3 C2C2 5 Sugar Sugar(deoxyribose)

19. 18 DNA 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

20. 19 Antiparallel Strands One strand of DNA goes from 5’ to 3’ (sugars) The other strand is opposite in direction going 3’ to 5’ (sugars)

21. 20 Nitrogenous Bases Double ring PURINESDouble ring PURINES Adenine (A) Guanine (G) Single ring PYRIMIDINESSingle ring PYRIMIDINES Thymine (T) Cytosine (C) T or C A or G

22. 21 Base-Pairings Purines only pair with Pyrimidines CG 3 H-bonds

23. 22 DNA Replication

24. 23 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

25. 24 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’

26. 25 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

27. 26 DNA Replication Before RNA primersBefore new DNA strands can form, there must be RNA primers present to start the addition of new nucleotides PrimasePrimase is the enzyme that synthesizes the RNA Primer DNA polymerase can then add the new nucleotides

28. 27 DNA Replication DNA polymerase can only add nucleotides to the 3’ end of the DNADNA 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’ directionThis causes the NEW strand to be built in a 5’ to 3’ direction RNAPrimer DNA Polymerase Nucleotide 5’ 3’ Direction of Replication

29. 28 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

30. 29 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’

31. 30 Synthesis of the New DNA Strands The Lagging Strand is discontinuouslyThe Lagging Strand is synthesized discontinuously against overall direction of replication RNA Primer Leading Strand DNA Polymerase 5’5’ 5’ 3’ Lagging Strand 5’ 3’

32. 31 Replication of Strands Replication Fork Point of Origin

33. 32 Proofreading New DNA DNA polymerase initially makes about 1 in 10,000 base pairing errorsDNA polymerase initially makes about 1 in 10,000 base pairing errors Enzymes proofread and correct these mistakesEnzymes proofread and correct these mistakes

34. 33 Semiconservative Model of Replication Idea presented by Watson & CrickIdea presented by Watson & Crick New DNA consists of 1 PARENTAL (original) and 1 NEW strand of DNA Parental DNA DNA Template New DNA

35. 34 DNA Damage & Repair Chemicals & ultraviolet radiation damage the DNA in our body cells Cells must continuously repair DAMAGED DNA

36. 35 Question: What would be the complementary DNA strand for the following DNA sequence? DNA 5’-CGTATG-3’

37. 36 Answer: DNA 5’-GCGTATG-3’ DNA 3’-CGCATAC-5’

38. 37