1. Chapter 12.1 DNA

2. Genetics Recap Mendel, through his experiments, concluded that a organism’s traits are a result of the inheritance of genes from that organism’s parents Mendel knew that this inheritance was due to some “factor” but was not able to identify what exactly it was –This left room for future scientists to discover what these mysterious factors were

3. Frederick Griffith Studied pneumonia and its effects on mice  Smooth strain caused pneumonia  Rough strain did nothing Injected mice with various mixtures of the two strains

4. Griffith’s Experiment 1.Living smooth cells injected = 2.Living rough cells injected = 3.Heat killed smooth cells = 4.Heat killed smooth cells & living rough cells = –Why did the mice die?

5. Griffith’s Conclusions Hypothesized that some factor was transferred from the heat-killed cells into the live cells Bacterial transformation occurred  a change in a bacterial trait Chemical is responsible for causing transformation  Called it the transforming principle Little did he know that he found DNA

6. Oswald Avery Tried to find out what factor caused the bacterial transformation  Destroyed all of the various macromolecules and tested to see if transformation still occurred  When he destroyed DNA, no transformation; proteins, lipids, and carbs still caused transformation Demonstrated that DNA was the transforming principle

7. Enzymes that destroy the macromolecules The fact that there is no S strain means that transformation did not happen DNA is the transforming principle

8. Hershey and Chase Used bacteriophages  viruses that attack bacteria  Consist of an outer protein coat and an inner core of DNA

9. How Do Bacteriophages Work? Bacteriophage lands on the plasma membrane of the bacteria Injects DNA into the bacteria Viral DNA inserts with bacterial DNA  gets duplicated when bacteria goes through mitosis More viruses will be produced and eventually the bacteria explodes releasing all of the new viruses http://www.youtube.com/watch?v=YG3d77SRWZI

10. Hershey and Chase Experiment Wanted to see what was responsible for causing transformation in bacteria –Was it the DNA inside the bacteriophage or the protein coat surrounding the bacteriophage Wanted to confirm Avery’s experiment  Labeled the protein coat with a radioactive sulfur isotope and the DNA with a radioactive phosphorous isotope so that they may follow where each part goes after the infection

11. Hershey and Chase Experiment Mixed solution of bacteriophage and solution of bacteria together and let virus work After a time, put mixture into a blender  Purpose was to shake viral coats off of the bacteria Because the cell is heavier it will go to the bottom of the blender –This part will have the DNA from the virus

12. Hershey and Chase Experiment

13. When observing the blender  found that the radioactive phosphorous was in the bottom part of the blender (inside the cells) while the radioactive sulfur was in the top part (empty protein coats) NOTConclusion – DNA causes transformation, NOT protein

14. DNA’s Responsibilities Genes carry information from one generation to the next Genes determine the heritable characteristics of organisms Genes can be replicated or copied exactly

15. DNA’s Components DNA is a nucleic acid –It has monomers called  nucleotides Each nucleotide is composed of three basic parts:  5 carbon sugar – deoxyribose  A phosphate group  A nitrogenous base

17. Nitrogenous Bases There are four nitrogenous bases categorized into two groups  Purines: (two rings) Adenine (A) Guanine (G)  Pyrimidines: (one ring) Cytosine (C) Thymine (T)

18. DNA’s Structure DNA can be considered to be like a ladder  The sugar and phosphate groups make up the backbone of the molecule, or the sides of the ladder –They alternate along the sides sugar  The nitrogenous bases stick out of the sides of the sugar –They make up the rungs of the ladder

20. Erwin Chargaff  Realized the number of A’s equals the number of T’s and that the number of G’s equals the number of C’s Base pairing rule A = TG = C Purines Pyrimidines

21. Rosalind Franklin  Used x-ray diffraction to gather information about DNA structure –Revealed that DNA is in helix form (coil or twisted ladder)

22. Watson and Crick Made 1 st 3-D model of a DNA molecule –Used the work of Chargaff and Franklin to create this model DNA structure is called a double helix, in which two strands are wound around each other  The two strands are connected by hydrogen bonds

24. DNA and Chromosomes  Chromosomes are tightly wound up DNA strands Increased organization allows for the tremendous length of DNA to fit into the nucleus of the cell

25. Chromosome Structure DNA is tightly wound around proteins called histones  8 histones + DNA = nucleosome –These form chromatin Chromatin tightly wound up makes a chromosome http://www.youtube.com/watch?v=yqESR7E4b_8&feature=related

26. Prokaryotic Chromosomes Prokaryotic chromosomes are located floating in the cytoplasm of the cell (not in the nucleus)  They are circular in shape (not “X shape” like in eukaryotes)