2. Chapter 12 DNA and Genes

3. Vocabulary: Transformation Bacteriophage Nucleotide Base pairing Double helix Key Concepts: What did scientists discover about the relationship between genes and DNA? What is the overall structure of the DNA molecule? DNA: The Molecule of Heredity

4. What we’ve learned so far… Cells make proteins Genetic information is passed on through chromosomes Compacted DNA and proteins= chromosomes Genetic information is stored in the nucleus Genetic information is essential so that each cell is identical (mitosis)

5. To truly understand genetics, biologists first had to discover the chemical nature of the gene. How do genes control what you look like? How do genes control what you look like?

6. Animal Husbandry Goat herders 5000 years ago knew … Offspring tend to look like their parents.

7. DNA’s “Experiment” History Fredrich Miescher (1869)  Studied pus cells he collected from bandages in hospitals  White blood cells are huge.  Used an enzyme to digest away the proteins in nucleus  A strange phosphorous molecule remained  Molecule of heredity?

8.  Griffith: How do certain types of bacteria cause pneumonia? The experiment that tested this question led to new knowledge. The experiment that tested this question led to new knowledge. Genetic information could be transformed from one bacterium to another. Genetic information could be transformed from one bacterium to another. Fredrick Griffith (1928)

9.  He injected mice with the one strain of bacteria and they died.  When he did the same with another strain of bacteria they didn’t die.  He could use heat to kill the deadly bacteria so it wouldn’t kill mice.  Injected mice with a mixture of harmless bacteria and the heat killed bacteria…

10. Genetic Info. Transferred

11.  The mice died!!  Something had passed from the heat killed deadly bacteria to the living harmless bacteria.  He called this process TRANSFORMATION.

12. Avery & DNA  Avery and a group of scientists decided to repeat Griffith’s experiment determine which molecule in the heat killed bacteria was needed for transformation determine which molecule in the heat killed bacteria was needed for transformation  Made an extract (juice) from heat killed bacteria and added enzymes that destroy  Made an extract (juice) from heat killed bacteria and added enzymes that destroy proteins, carbohydrates, & lipids Transformation still occurred! Transformation still occurred!  Repeated the experiment but added enzymes that destroy DNA Transformation DID NOT occur!! Transformation DID NOT occur!!

13. Avery’s Conclusion  What was the “transforming factor”?  DNA  Conclusion: DNA is the nucleic acid that stores and transmits genetic info from generation to generation

14. Hershey-Chase Experiment (1952)  Studied viruses; specifically bacteriophages Bacterio = bacteria Bacterio = bacteria Phage = eater Phage = eater Bacteria eater Bacteria eater  Viruses—made up of: DNA + protein coat DNA + protein coat  Research Question: Which part of the virus enters the infected bacteria cell?

15. Hershey & Chase  Wanted to REALLY make sure it was DNA  Viruses are made of only protein and DNA  Proteins have sulfur but no phosphorous.  DNA has phosphorous but no sulfur Bacteriophage

16.  Grew viruses in the presence of radioactive markers P and S.  Grew viruses in the presence of radioactive markers P 32 and S 35. Sulfur is found in protein coat Sulfur is found in protein coat Phosphorus is found in DNA Phosphorus is found in DNA

17. Hershey-Chase Conclusion  Genetic information of the bacteriophage that they infected with bacteria was DNA NOT protein NOT protein

18. What DNA does…  Deoxyribonucleic Acid = DNA  Carries information from one generation to the next  Put that information to work by determining heritable characteristics  Must be easily copied since almost every new cell gets a copy

19. DNA Structure  Made up of nucleotides (monomer)  Each composed of 3 parts: Deoxyribose: sugar Deoxyribose: sugar Phosphate group Phosphate group Nitrogenous (nitrogen containing) base Nitrogenous (nitrogen containing) base Adenine (A)Adenine (A) Thymine (T)Thymine (T) Guanine (G)Guanine (G) Cytosine (C)Cytosine (C)

20.  Backbone Deoxyribose & Phosphate Group of each nucleotide Deoxyribose & Phosphate Group of each nucleotide  “Steps of Ladder” bases bases   Any base sequence is possible DNA Structure = Double Helix

21. Chargaff’s Rules What does this data suggest to you? Percentage of Bases in Four Organisms Source of DNA ATGC Streptococcus29.831.620.518.0 Yeast31.332.918.717.1 Herring27.827.522.222.6 Human30.929.419.919.8

22. Oooooohhhh!! Aaaaaahhhhh!!!!  A = T (A pairs with T)  C = G (C pairs with G)

23. What DNA Looks Like  Rosalind Franklin: used X-Ray diffraction patterns to discover that DNA twisted around each other like a helix

24.  Watson & Crick: while trying to build a 3-D model of DNA, Watson was shown Franklin’s photograph and within weeks, figured out the structure of DNA

25. What’s holding the strands together?  HYDROGEN BONDS!!!  Hydrogen Bonds form between A and T base pairs as well as between C and G base pairs