Chapter 12.1 DNA

1. Chapter 12.1DNA

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

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. Hershey and Chase Experiment • 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) • Conclusion – 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 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 PurinesPyrimidines

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 1st 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)