2. AP Biology D.N.A  Once the bell rings, please take out your pencil and prepare to finish the Unit 4 Genetics Test  You will have 20 minutes

3. AP Biology ANNOUNCEMENTS  AP BIOLOGY MIDTERM IS ON FRIDAY JANUARY 28 th at 8 am

4. AP Biology 2006-2007 DNA The Genetic Material UNIT 8: MOLECULAR BIOLOGY

5. AP Biology Genes are on chromosomes  Morgan’s conclusions  genes are on chromosomes  but is it the protein or the DNA of the chromosomes that are the genes?  initially proteins were thought to be genetic material… Why? 1908 | 1933 What’s so impressive about proteins?!

6. AP Biology The “Transforming Principle” 1928  Frederick Griffith  Streptococcus pneumonia bacteria  was working to find cure for pneumonia  harmless live bacteria (“rough”) mixed with heat-killed pathogenic bacteria (“smooth”) causes fatal disease in mice  a substance passed from dead bacteria to live bacteria to change their phenotype  “Transforming Principle”

7. AP Biology The “Transforming Principle” Transformation = change in phenotype something in heat-killed bacteria could still transmit disease-causing properties live pathogenic strain of bacteria live non-pathogenic strain of bacteria mice diemice live heat-killed pathogenic bacteria mix heat-killed pathogenic & non-pathogenic bacteria mice livemice die A.B. C. D.

8. AP Biology DNA is the “Transforming Principle”  Avery, McCarty & MacLeod  purified both DNA & proteins separately from Streptococcus pneumonia bacteria  which will transform non-pathogenic bacteria?  injected protein into bacteria  no effect  injected DNA into bacteria  transformed harmless bacteria into virulent bacteria 1944 What’s the conclusion? mice die

9. AP Biology 1952 – Alfred Hershey & Martha Chase  Is it protein or DNA that is the genetic material?  Used bacteriophages (viruses that infect bacteria) to show that since DNA enters the bacterial cells, but protein doesn’t, DNA must be the genetic material

10. AP Biology Chargaff  DNA composition: “Chargaff’s rules”  varies from species to species  all 4 bases not in equal quantity  humans: A = 30.9% T = 29.4% G = 19.9% C = 19.8% 1947 That’s interesting! What do you notice? Rules A = T C = G

11. AP Biology Early 1950s – Maurice Wilkins & Rosalind Franklin  Rosalind Franklin took X-ray crystallography diffraction photograph of DNA

12. AP Biology 1953 – James Watson & Francis Crick  Constructed model of DNA as a double helix  Purine + pyrimidine for consistent width  C-G  3 hydrogen bonds  A-T  2 hydrogen bonds

13. AP Biology Late 1950s – Matthew Meselson & Franklin Stahl  Semi-conservative replication of DNA  Each new molecule of DNA (after DNA replication) contains 1 old and 1 new strand

14. AP Biology But how is DNA copied?  Replication of DNA  base pairing suggests that it will allow each side to serve as a template for a new strand “It has not escaped our notice that the specific pairing we have postulated immediately suggests a possible copying mechanism for the genetic material.”— Watson & Crick

15. AP Biology proteinRNA The “Central Dogma” DNA transcriptiontranslation replication  Flow of genetic information in a cell

16. AP Biology The Structure of DNA  Double helix  Each nucleotide is made up of:  Deoxyribose (sugar)  A phosphate group  A nitrogenous base  Adenine, guanine, cytosine, thymine  A, G = purines  2 carbon rings  C, T = pyrimidines  1 carbon ring

17. AP Biology The Structure of DNA  Base-Pairing Rules: (Chargaff’s Rules)  Guanine pairs with cytosine  Thymine pairs with adenine  DNA strands are antiparallel  They run in opposite directions  5’ and 3’ ends

18. AP Biology DNA Replication  Big Picture:  A new and identical molecule of DNA is made, using the old one as a template  Occurs in the nucleus

19. AP Biology DNA Replication  DNA replication begins at the origin of replication, a special sequence of DNA  2 strands are separated by the enzyme, helicase, forming a replication bubble  Replication fork is formed at each end of the replication bubble

20. AP Biology DNA Replication  At replication fork, nucleotides “line up” with their complementary mates, according to the base- pairing rules  DNA polymerase III attaches the nucleotides to the exposed bases of the DNA strand

21. AP Biology DNA Replication: A Summary

22. AP Biology Leading Strand  DNA replication is different on the 2 strands  Along one template strand, the leading strand, DNA polymerase III just follows the replication fork (replicates continuously in one strand)  Polymerase III only synthesizes DNA from 5’ to 3’

23. AP Biology Lagging Strand  On the other strand of DNA, the lagging strand – DNA polymerase must work in the opposite direction of the replication fork  Short segments of DNA– Okazaki fragments – are made  Okazaki fragments are joined by DNA ligase

24. AP Biology

26. DNA Proofreading  DNA polymerase I proofreads each nucleotide as it is added to the DNA strand  If there’s a mistake…  it backs up  removes the wrong nucleotide  adds the right nucleotide

27. AP Biology Enzymes & Their Job in Replication  Helicases- unwind the DNA strand  Single strand binding protein- holds the single strands apart for replication.  RNA – initiates DNA replication  DNA Polymerase III- adds complementary bases to 3’ end of primer or new DNA strand.  DNA Polymerase I- removes RNA primer & inserts DNA nucleotides. (also proofreads)  DNA Ligase- “sews” Okasaki fragments of lagging strand together with covalent bonds.