DNA

1. DNA

2. DNA • Deoxyribose Nucleic Acid • Carries the information for carrying out the activities of the cell

4. History of DNA • First discovered in 1869 • 1928 – Griffith – bacteria transformation • 1952 – Hershey and Chase – virus experiment • 1953 - Watson and Crick determined structure of DNA

5. Head DNA Tail Tailfiber 300,000 • Hershey – Chase experiments showed that DNA is the genetic material • Viruses replicate by injecting their DNA into host cells Figure 10.1A

6. Hershey Chase Experiment • Used 2 different radioactive isotopes: • 1. Add isotopes • Sulfur  indicates protein • Phosphorous  indicates DNA • 2. Allow both batches to infect nonradioactive bacteria • 3. Agitate in blender • 4. Centrifuge sample • 5. Observe pellet (cells) for radioactivity

7. Radioactive protein Empty protein shell Bacterium Radioactivityin liquid Phage Phage DNA DNA Batch 1Radioactiveprotein Centrifuge Pellet Mix radioactively labeled phages with bacteria. The phages infect the bacterial cells. Measure the radioactivity in the pellet and the liquid. Agitate in a blender to separate phages outside the bacteria from the cells and their contents. Centrifuge the mixture so bacteria form a pelletat the bottom of the testtube. 1 2 3 4 Radioactive DNA Batch 2RadioactiveDNA Centrifuge Radioactivityin pellet Pellet Figure 10.1B • The Hershey-Chase experiment

9. In Stockholm for their Nobel Prizes, December 1962:Maurice Wilkins, John Steinbeck, John Kendrew, Max Perutz, Francis Crick, and James D Watson.

11. Figure 10.3A, B

12. Nucleotides • What DNA is made of • Deoxyribose, a phosphate group, nitrogen base

13. Nucleotides • S -----N B • P

15. Adenine Thymine Guanine Cytosine A T G C Nitrogen Bases

21. Pyrimidines: the smaller bases • Has 1 organic ring • T,C • Purines: the bigger bases • Has 2 organic rings • A, G

22. Purine Pyrimidine

23. H H H H O N N O C H C H H3C C C H N N N C C N C N N C H H C C C C C C C C C C H O H N N N O H N N H N N H H H H H Adenine (A) Guanine (G) Thymine (T) Cytosine (C) Purines Pyrimidines Figure 10.2B

24. DNA • 2 long chains of nucleotides arranged in a spiral • Double Helix • Base Pairing: A --- T, G --- C

25. 5 end 3 end P HO 5 4 2 3 A T 3 1 1 4 2 5 P P C G P P G C P P A T OH P 3 end 5 end • Each strand of the double helix • Is oriented in the opposite direction Figure 10.5B

26. Sugar-phosphate backbone Phosphate group Nitrogenous base A A Sugar Nitrogenous base(A, G, C, or T) Phosphategroup C C DNA nucleotide O H H3C C C N O C C T CH2 H T O P N O O O– Thymine (T) O C C H H H H G G C C H O Sugar(deoxyribose) T T DNA nucleotide DNA polynucleotide Figure 10.2A

27. Twist Figure 10.3C

28. G C O T A OH P Hydrogen bond –O O A T OH O H2C A T Basepair O CH2 O O C G P O O– –O C G O P O H2C O O C T G A O CH2 C G O O P O O– – O O P O H2C O O G C A T O CH2 O O A T P O – O O– O P A T O O H2C O A T A T CH2 O OH O O– P G C HO O T A Partial chemical structure Ribbon model Computer model Figure 10.3D

30. Replication • Process of how the DNA code is copied • Occurs in Interphase of Cell Cycle and Interphase I of meiosis • New strands of DNA are made from a supply of nucleotides that float freely in the nucleus

32. Replication • 1. Enzyme, Helicase, breaks the H bonds between the base pairs • 2. Helix unzips, exposing the bases

33. Replication • 3. Free floating nucleotides pair with the exposed bases • Done by DNA polymerase • Speed – nucleotides are added at a rate of 50 per second in mammals; 500 per second in bacteria

35. T A T T A A T A T A G C G G G C C C G C C C G G G C G C C A A T A T A A T T A T T T A A A T Both parental strands serve as templates Two identical daughtermolecules of DNA Parental moleculeof DNA DNA REPLICATION Nucleotides Figure 10.4A

36. Replication Forks • Origins of replication • The sites at which separation and replication occur

37. Parental strand Origin of replication Daughter strand Bubble Two daughter DNA molecules Figure 10.5A

38. DNA polymerase adds nucleotides only to the 3’ end of the strand. • The daughter DNA strand can only grow in the 5’ -> 3’ direction

42. Leading Strand: DNA strand made in the 5’ – 3’ direction • Forms 1 continuous strand • Lagging Strand: DNA strand made in the 3’ – 5’ direction • Forms Okazaki fragments • DNA ligase joins fragments

45. DNA polymerase molecule 3 5 Daughter strandsynthesizedcontinuously Parental DNA 5 3 Daughter strandsynthesizedin pieces 3 5 5 3 DNA ligase Overall direction of replication Figure 10.5C

46. G C T A G C G C A T T A C G A T C G G C C G G C C C G G A C A T A T T G A T T G T T A A A A A C T T T A Figure 10.4B