12–1 DNA

1. 12–1 DNA

2. Griffith and Transformation • Griffith and Transformation • In 1928, British scientist Fredrick Griffith was trying to learn how certain types of bacteria caused pneumonia. • He isolated two different strains of pneumonia bacteria from mice and grew them in his lab.

3. Griffith and Transformation • Griffith made two observations: • (1) The disease-causing strain of bacteria grew into smooth colonies on culture plates. • (2) The harmless strain grew into colonies with rough edges.

4. Griffith and Transformation • Griffith's Experiments • Griffith set up four individual experiments. • Experiment 1: Mice were injected with the disease-causing strain of bacteria. The mice developed pneumonia and died.

5. Griffith and Transformation • Experiment 2: Mice were injected with the harmless strain of bacteria. These mice didn’t get sick. Harmless bacteria (rough colonies) Lives

6. Griffith and Transformation • Experiment 3: Griffith heated the disease-causing bacteria. He then injected the heat-killed bacteria into the mice. The mice survived. Heat-killed disease-causing bacteria (smooth colonies) Lives

7. Griffith and Transformation Heat-killed disease-causing bacteria (smooth colonies) • Experiment 4: Griffith mixed his heat-killed, disease-causing bacteria with live, harmless bacteria and injected the mixture into the mice. The mice developed pneumonia and died. Harmless bacteria (rough colonies) Live disease-causing bacteria(smooth colonies) Dies of pneumonia

8. Griffith and Transformation Heat-killed disease-causing bacteria (smooth colonies) • Griffith concluded that the heat-killed bacteria passed their disease-causing ability to the harmless strain. Harmless bacteria (rough colonies) Live disease-causing bacteria(smooth colonies) Dies of pneumonia

9. Griffith and Transformation • Transformation  • Griffith called this process transformation because one strain of bacteria (the harmless strain) had changed permanently into another (the disease-causing strain). • Griffith hypothesized that a factor must contain information that could change harmless bacteria into disease-causing ones.

11. Station 1 Puzzle:

12. Avery and DNA • Avery and DNA • Oswald Avery repeated Griffith’s work to determine which molecule was most important for transformation. • Avery and his colleagues made an extract* from the heat-killed bacteria that they treated with enzymes. • *liquefied cells that allow all of the molecules to be exposed instead of protected by the cell membrane.

13. Avery and DNA • The enzymes destroyed proteins, lipids, carbohydrates, and other molecules, including the nucleic acid RNA. • Transformation still occurred. • This shocked many scientists, because many thought proteins would be the material for heredity since it is complex and widely found in the bodies of all living things.

14. Avery and DNA • Avery and other scientists repeated the experiment using enzymes that would break down DNA. • When DNA was destroyed, transformation did not occur. Therefore, they concluded that DNA was the transforming factor.

16. Avery and DNA • Avery and other scientists discovered that the nucleic acid DNA stores and transmits the genetic information from one generation of an organism to the next.

17. Station 2 Puzzle:

18. The Hershey-Chase Experiment • The Hershey-Chase Experiment • Alfred Hershey and Martha Chase studied viruses—nonliving particles smaller than a cell that can infect living organisms.

19. The Hershey-Chase Experiment • Bacteriophages  • A virus that infects bacteria is known as a bacteriophage. • Bacteriophages are composed of a DNA or RNA core and a protein coat.

20. The Hershey-Chase Experiment • When a bacteriophage enters a bacterium, the virus attaches to the surface of the cell and injects its genetic information into it. • The viral genes produce many new bacteriophages, which eventually destroy the bacterium. • When the cell splits open, hundreds of new viruses burst out.

21. The Hershey-Chase Experiment • If Hershey and Chase could determine which part of the virus entered an infected cell, they would learn whether genes were made of protein or DNA. • They grew viruses in cultures containing radioactive isotopes of phosphorus-32 (32P) and sulfur-35 (35S).

22. The Hershey-Chase Experiment • If 35S was found in the bacteria, it would mean that the viruses’ protein had been injected into the bacteria. Phage infects bacterium Bacteriophage with suffur-35 in protein coat No radioactivity inside bacterium

23. The Hershey-Chase Experiment • If 32P was found in the bacteria, then it was the DNA that had been injected. Bacteriophage with phosphorus-32 in DNA Phage infects bacterium Radioactivity inside bacterium

25. The Hershey-Chase Experiment • Nearly all the radioactivity in the bacteria was from phosphorus (32P). • Hershey and Chase concluded that the genetic material of the bacteriophage was DNA, not protein.

26. Station 3 Puzzle: • In a one-story pink house, there was a pink person, a pink cat, a pink fish, a pink computer, a pink chair, a pink table, a pink telephone, a pink shower– everything was pink!What color were the stairs?

27. The Components and Structure of DNA • Chargaff's Rules Erwin Chargaff discovered that: • the number of adenine (A) bases always equals the number of thymine (T) bases; • the number of guanine (G) bases always equals the number of cytosine (C) bases; • the number of purines (A+G) always equals the number of pyrimidines (T+C) — this rule is an obvious consequence of rules 1 and 2. Rumor has it that he met with Watson and Crick at the bar on Cambridge University’s campus, where after a few drinks he explained the above to them. Watson and Crick did not credit him for the help.

28. Station 5 Puzzle: • If a strip of DNA is made up of 30% Adenine, how much Guanine is there?

29. The Components and Structure of DNA • X-Ray Evidence  • King’s college scientists Maurice Wilkins and Rosalind Franklin were using X-ray Crystalography to study DNA and to determine the structure of DNA. • Rosalind Franklin took the photo on the top right. The X shape means that DNA is helical.

30. Watson managed to view Franklin’s photo; some say through nefarious means, others say that it was freely available information. • It is safe to assume that without the photo, Watson and Crick would not have discovered the structure of DNA. • All involved in the search for the structure were awarded the nobel prize, except Rosalind Franklin, because she had passed away prior to award, and thus was ineligible due to being dead.

31. Station 4 Puzzle:

32. The Components and Structure of DNA • The Double Helix  • Using clues from Franklin’s pattern, James Watson and Francis Crick built a model that explained how DNA carried information and could be copied. • Watson and Crick's model of DNA was a double helix, in which two strands were wound around each other.

33. The Components and Structure of DNA • Watson and Crick discovered that hydrogen bonds can form only between certain base pairs—adenine and thymine, and guanine and cytosine. • This principle is called base pairing.

34. The Components and Structure of DNA • The Components and Structure of DNA • DNA is made up of nucleotides. • nucleotide = a five-carbon sugar [deoxyribose] • a phosphate group • a nitrogenous base.

35. The Components and Structure of DNA • There are four kinds of bases in in DNA: • adenine • guanine • cytosine • thymine

36. The Components and Structure of DNA • The backbone of a DNA chain is formed by sugar and phosphate groups of each nucleotide. • The nucleotides can be joined together in any order. Sugar Phosphate Backbone

37. The Components and Structure of DNA • DNA Double Helix

38. Station 6 Puzzle: How Many triangles are there?