1. DNA Structure and Function

2. Miescher Discovered DNA 1868 Johann Miescher investigated the chemical composition of the nucleus Isolated an organic acid that was high in phosphorus He called it nuclein We call it DNA (deoxyribonucleic acid)

3. Mystery of the Hereditary Material Originally believed to be an unknown class of proteins Thinking was –Heritable traits are diverse –Molecules encoding traits must be diverse –Proteins are structurally diverse; so the hereditary material must be protein Wrong!

4. Griffith Discovers Transformation 1928 Attempting to develop a vaccine Isolated two strains of Streptococcus pneumoniae –Rough strain was harmless –Smooth strain was pathogenic

5. Griffith Discovers Transformation 1. Mice injected with live cells of harmless strain R. 2. Mice injected with live cells of killer strain S. 3. Mice injected with heat-killed S cells. 4. Mice injected with live R cells plus heat- killed S cells. Mice die. Live S cells in their blood. Mice live. No live R cells in their blood. Mice die. Live S cells in their blood. Mice live. No live S cells in their blood. Figure 13.3 Page 218

6. Transformation What happened in the fourth experiment? The harmless R cells had been transformed by material from the dead S cells Descendents of the transformed cells were also pathogenic

7. Oswald Avery Cell extracts treated with protein-digesting enzymes could still transform bacteria Cell extracts treated with DNA-digesting enzymes lost their transforming ability Concluded that DNA, not protein, transforms bacteria Some substance from the S cells had transformed the R cells. a.Both proteins and nucleic acids were candidates. b.In 1944, Oswald Avery showed that the substance was DNA.

8. Hershey & Chase’s Experiments Created labeled bacteriophages –Radioactive sulfur –Radioactive phosphorus Allowed labeled viruses to infect bacteria Asked: Where are the radioactive labels after infection?

9. virus particle labeled with 35 S virus particle labeled with 32 P bacterial cell (cutaway view) label outside cell label inside cell Hershey and Chase Results Figure 13.5 Page 219

10. Structure of Nucleotides in DNA Each nucleotide consists of –Deoxyribose (5-carbon sugar) –Phosphate group –A nitrogen-containing base Four bases –Adenine, Guanine, Thymine, Cytosine

11. Nucleotide Bases phosphate group deoxyribose ADENINE (A) THYMINE (T) CYTOSINE (C) GUANINE (G) Figure 13.6 Page 220 purines pyrimadines

12. Composition of DNA Chargaff showed: –Amount of adenine relative to guanine differs among species –Amount of adenine always equals amount of thymine and amount of guanine always equals amount of cytosine A=T and G=C

13. Rosalind Franklin’s Work Was an expert in X-ray crystallography Used this technique to examine DNA fibers Concluded that DNA was some sort of helix

14. Watson-Crick Model DNA consists of two nucleotide strands Strands run in opposite directions Strands are held together by hydrogen bonds between bases A binds with T and C with G Molecule is a double helix

15. DNA is double stranded and analogous to a ladder. The sides of the ladder are composed of alternating sugars (deoxyribose) and phosphate groups that run antiparell to one another. On the left side (in the picture) the first carbon found on the strand is #5 and moving on down the last carbon is carbon # 3. This side is said to be 5'-3'. The opposite side is upside down compared to the other side. The right hand side, the first carbon found on the strand is #3 and moving on down the last carbon is carbon # 5. This side is said to be 3'-5‘.

16. Watson-Crick Model Figure 13.7 Page 221

18. DNA Structure Helps Explain How It Duplicates DNA is two nucleotide strands held together by hydrogen bonds Hydrogen bonds between two strands are easily broken Each single strand then serves as template for new strand

19. DNA Replication new old Each parent strand remains intact Every DNA molecule is half “old” and half “new” Semicomservative (Meslson and Stahl) Figure 13.9 Page 222

20. After 1 replication, they found that the “new” strands were hybrids (contained both heavy and light). Meslson and Stahl Experiment After 2 replications, they found that the some “new” strands were hybrids and some were only light.

21. Their results supported the idea of semi-conservative replication.

22. Base Pairing during Replication Each old strand serves as the template for complementary new strand Figure 13.10 Page 223

23. -Because DNA is such a long molecule, replication must occur at the same time. -micrograph of 3 replication bubbles

24. Enzymes in Replication Helicase unwinds and separates the two strands opening the template single stranded binding proteins stabilize the unwound parental strands topoisomerase (or gyrase) relieves stress on strands by breaking, swiveling and rejoining the parental strand at the start of the replication fork Primase makes RNA primers so DNA polymerase has something to hook onto DNA polymerase attaches complementary nucleotides DNA ligase fills in gaps Enzymes wind two strands together

25. -DNA polymerase can only add to the 3' end of a nucleotide. This means that synthesis can only occur from the 5’ to 3' direction. -DNA polymerase must always have a nucleotide in front of it to hang the DNA nucleotide on. Therefore an RNA primer must be laid down first and then replaced by DNA polymerase

26. A Closer Look at Strand Assembly Energy for strand assembly is provided by removal of two phosphate groups from free nucleotides newly forming DNA strand one parent DNA strand Figure 13.10 Page 223

27. Continuous and Discontinuous Assembly Strands can only be assembled in the 5’ to 3’ direction Figure 13.10 Page 223

29. http://www.johnkyrk.com/DNAreplication.html http://www.fed.cuhk.edu.hk/~johnson/teachin g/genetics/animations/dna_replication.htm

30. DNA Repair Mistakes can occur during replication DNA polymerase can read correct sequence from complementary strand and, together with DNA ligase, can repair mistakes in incorrect strand DNA polymerases "proofread” the new bases for mismatched pairs, which are replaced with correct bases

31. Cloning Making a genetically identical copy of an individual Researchers have been creating clones for decades