DNA Structure and Function Crash Course

1. DNA Structure and FunctionCrash Course: http://www.youtube.com/watch?NR=1&feature=fvwp&v=8kK2zwjRV0M Chapter 12

2. Chapter Mystery: UV Light • UV light can damage cells and kills nearly 10,000 Americans a year due to skin cancer. . . • BUT why is sunlight so dangerous? ?

3. What part of our cells does UV damage?

4. Early and Puzzling Clues • 1860s: Frederich Miescher found DNA (deoxyribonucleic acid) in nuclei of cells. Easy to extract, but what is its function? • Early 1920s: Griffith transferred hereditary material from dead cells to live cells—used pneumonia bacteria

5. R R S A Mice injected with live cells of harmless strain R do not die. Live R cells are in their blood. B Mice injected with live cells of killer strain S die. Live S cells are in their blood. C Mice injected with heat-killed S cells do not die. No live S cells are in their blood. D Mice injected with live R cells plus heat-killed S cells die. Live S cells are in their blood. Griffith’s pneumonia experiments. . . Stepped Art Fig. 13-2, p. 204

6. Avery and McCarty • 1940: Avery and McCarty separated deadly S cells (from Griffith’s experiments) into lipid, protein, and nucleic acid components, then repeated Griffith’s experiments • Conclusion: DNA is the “transforming principle”

7. Study Question! • The process by which one strain of bacterium is apparently changed into another strain is called? • Transcription • Transformation • Duplication • Replication

8. Answer • Transformation !

9. The Hershey-Chase Experiments

10. Confirmation of DNA’s Function • 1950s: Hershey and Chase experimented with bacteriophages (viruses that infect bacteria) • Protein parts of viruses, labeled with 35S, stayed outside the bacteria • DNA of viruses, labeled with 32P, entered the bacteria • Conclusion: DNA, not protein, is the material that stores hereditary information

11. So, where is the DNA?

12. Chromosome Structure • DNA is wound into chromosomes in the nucleus

13. How was DNA’s structure discovered?

14. Chargaff’s Rules • 1950: Erwin Chargaff found that the amounts of thymine and adenine in DNA are the same, and the amounts of cytosine and guanine are the same. • The amount of A = T and G = C

15. Chargaff’s results:

16. The Discovery of DNA’s Structure • James Watson and Francis Crick’s discovery of DNA’s structure was based on almost fifty years of research by other scientists • They won the Nobel Prize with Maurice Wilkins in 1962 for the structure

17. Study Question • According to Chargaff’s rule base pairing, which of the following is true about DNA? • A=T and C=G • A=C and T=G • A=G and T=C • A=T=G=C

18. Answer! a. A=T and C=G

19. Rosalind Franklin’s Image • Rosalind Franklin’s research in x-ray crystallography revealed the dimensions and shape of the DNA molecule: an alpha helix • Watson and Crick used the photo to build their model of DNA • Franklin died of cancer at age 37, possibly related to extensive exposure to x-rays

20. Parts of DNA 1. Phosphate 2. Deoxyribose Sugar 3. A Nucleic Acid (A, T, C or G) Also called a “nitrogenous base” Add all three of these parts to make one side of the DNA ladder called anucleotide

21. Building the double helix • Now, each nucleotide can be bonded together in the middle to complete both sides of the ladder. • A bonds with T and C bonds with G

22. DNA’s Building Blocks • Nucleotide • A nucleic acid monomer consisting of • a five-carbon sugar (deoxyribose) • a phosphate group • and one of four nitrogen-containing bases (nucleic acids) • DNA consists of four nucleotide building blocks • Two pyrimidines: thymine and cytosine • Two purines: adenine and guanine

23. STUDY Question! • What the three components DNA?

24. ANSWER! • Phosphate • Sugar • Nucleic Acid

25. 12.3 DNA Replication and Repair When do cells need to copy their DNA? • A cell copies its DNA before mitosis or meiosis I • DNA repair mechanisms and proofreading correct most replication errors

26. Enzymes of DNA Replication • DNA helicase • Breaks hydrogen bonds between DNA strands • DNA polymerase • Joins free nucleotides into a new strand of DNA • DNA ligase • Joins DNA segments on discontinuous strand DNA Replication: http://www.youtube.com/watch?v=4jtmOZaIvS0

27. A A DNA molecule is double-stranded. The two strands of DNA stay zippered up together because they are complementary: their nucleotides match up according to base-pairing rules (G to C, T to A). B As replication starts, the two strands of DNA are unwound. In cells, the unwinding occurs simul- taneously at many sites along the length of each double helix. C Each of the two parent strands serves as a template for assembly of a new DNA strand from free nucleotides, according to base-pairing rules (G to C, T to A). Thus, the two new DNA strands are complementary in sequence to the parental strands. D DNA ligase seals any gaps that remain between bases of the “new” DNA, so a continuous strand forms. The base sequence of each half-old, half-new DNA molecule is identical to that of the parent DNA molecule. Stepped Art Fig. 13-6, p. 208

28. Semiconservative Replication of DNA

29. Discontinuous Synthesis of DNA

30. A Each DNA strand has two ends: one with a 5’ carbon, and one with a 3’ carbon. DNA polymerase can add nucleotides only at the 3’ carbon. In other words, DNA synthesis proceeds only in the 5’ to 3’ direction. Fig. 13-8a, p. 209

31. Checking for Mistakes • DNA repair mechanisms • DNA polymerases proofread DNA sequences during DNA replication and repair damaged DNA • When proofreading and repair mechanisms fail, an error becomes a mutation – a permanent change in the DNA sequence

32. The whole story of DNA Replication • . . .as told by N Sync: http://www.youtube.com/watch?v=dIZpb93NYlw