121 DNA Slide 2 of 37 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. 121 DNA Slide 3 of 37 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. 121 DNA Slide 4 of 37 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. 121 DNA Slide 5 of 37 Griffith and Transformation Experiment 2: Mice were injected with the harmless strain of bacteria. These mice didnt get sick. Harmless bacteria (rough colonies) Lives 121 DNA Slide 6 of 37 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 121 DNA Slide 7 of 37 Griffith and Transformation 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. Live disease- causing bacteria (smooth colonies) Dies of pneumonia Heat-killed disease- causing bacteria (smooth colonies) Harmless bacteria (rough colonies) 121 DNA Slide 8 of 37 Griffith and Transformation Griffith concluded that the heat-killed bacteria passed their disease- causing ability to the harmless strain. Live disease- causing bacteria (smooth colonies) Heat-killed disease- causing bacteria (smooth colonies) Harmless bacteria (rough colonies) Dies of pneumonia 121 DNA Slide 9 of 37 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. 121 DNA Slide 10 of 37 121 DNA Slide 11 of 37 Station 1 Puzzle: 121 DNA Slide 12 of 37 Avery and DNA Oswald Avery repeated Griffiths 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. 121 DNA Slide 13 of 37 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. 121 DNA Slide 14 of 37 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. 121 DNA Slide 15 of 37 121 DNAAvery 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. 121 DNA Station 2 Puzzle: 121 DNA Slide 18 of 37 The Hershey-Chase Experiment Alfred Hershey and Martha Chase studied virusesnonliving particles smaller than a cell that can infect living organisms. 121 DNA Slide 19 of 37 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. 121 DNA Slide 20 of 37 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. 121 DNA Slide 21 of 37 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 ( 32 P) and sulfur-35 ( 35 S). 121 DNA Slide 22 of 37 The Hershey-Chase Experiment If 35 S was found in the bacteria, it would mean that the viruses protein had been injected into the bacteria. Bacteriophage with suffur-35 in protein coat Phage infects bacterium No radioactivity inside bacterium 121 DNA Slide 23 of 37 The Hershey-Chase Experiment If 32 P 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 121 DNA Slide 24 of 37 121 DNAThe Hershey-Chase Experiment Nearly all the radioactivity in the bacteria was from phosphorus ( 32 P). not protein Hershey and Chase concluded that the genetic material of the bacteriophage was DNA, not protein. 121 DNA 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? 121 DNA Slide 27 of 37 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 Universitys campus, where after a few drinks he explained the above to them. Watson and Crick did not credit him for the help. 121 DNA Slide 28 of 37 Station 5 Puzzle: If a strip of DNA is made up of 30% Adenine, how much Guanine is there? 121 DNA Slide 29 of 37 The Components and Structure of DNA X-Ray Evidence Kings 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. 121 DNA Slide 30 of 37 Watson managed to view Franklins 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. 121 DNA Slide 31 of 37 Station 4 Puzzle: 121 DNAThe Components and Structure of DNA The Double Helix Using clues from Franklins 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. 121 DNA Slide 33 of 37 The Components and Structure of DNA Watson and Crick discovered that hydrogen bonds can form only between certain base pairsadenine and thymine, and guanine and cytosine. This principle is called base pairing. 121 DNA Slide 34 of 37 The Components and Structure of DNA DNA is made up of nucleotides. nucleotide = a five-carbon sugar [deoxyribose] a phosphate group a nitrogenous base. 121 DNA Slide 35 of 37 The Components and Structure of DNA There are four kinds of bases in in DNA: adenine guanine cytosine thymine 121 DNA Slide 36 of 37 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 121 DNA Slide 37 of 37 The Components and Structure of DNA DNA Double Helix 121 DNA Slide 38 of 37 Station 6 Puzzle: How Many triangles are there?