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Biology Slide 1 of 37 Copyright Pearson Prentice Hall End Show 12–1 DNA Slide 2 of 37 Copyright Pearson Prentice Hall End Show 12–1 DNA Griffith and Transformation In 1928, British scientist Fredrick Griffith was trying to learn how certain types of bacteria caused pneumonia. Slide 3 of 37 Copyright Pearson Prentice Hall End Show He isolated two different strains of pneumonia bacteria from mice and grew them in his lab. 12–1 DNA 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. Slide 5 of 37 Copyright Pearson Prentice Hall End Show 12–1 DNA Griffith and Transformation Griffith's Experiments Slide 6 of 37 Copyright Pearson Prentice Hall End Show 12–1 DNA Griffith and Transformation Experiment 2: Harmless bacteria (rough colonies) Lives Copyright Pearson Prentice Hall Slide 7 of 37 End Show 12–1 DNA Griffith and Transformation Experiment 3: Heat-killed diseasecausing bacteria (smooth colonies) Lives Copyright Pearson Prentice Hall Slide 8 of 37 End Show 12–1 DNA Griffith and Transformation Experiment 4: Dies of pneumonia Copyright Pearson Prentice Hall Slide 9 of 37 End Show 12–1 DNA Griffith and Transformation Heat-killed diseasecausing bacteria (smooth colonies) Griffith concluded that the heat-killed bacteria passed their diseasecausing ability to the harmless strain. Live disease- Harmless bacteria (rough colonies) causing bacteria (smooth colonies) Dies of pneumonia Copyright Pearson Prentice Hall Slide 10 of 37 End Show 12–1 DNA Griffith and Transformation Griffith called this process transformation because one strain of bacteria (the harmless strain) had changed permanently into another (the diseasecausing strain). Griffith hypothesized that a factor must contain information that could change harmless bacteria into disease-causing ones. Slide 11 of 37 Copyright Pearson Prentice Hall End Show 12–1 DNA Avery and DNA Oswald Avery repeated Griffith’s work to determine which molecule was most important for transformation. Slide 12 of 37 Copyright Pearson Prentice Hall End Show Avery and his colleagues made an extract from the heat-killed bacteria that they treated with enzymes. 12–1 DNA Avery and DNA The enzymes destroyed proteins, lipids, carbohydrates, and other molecules, including the nucleic acid RNA. Transformation still occurred. Slide 14 of 37 Copyright Pearson Prentice Hall End Show 12–1 DNA 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. Copyright Pearson Prentice Hall Slide 15 of 37 End Show What did scientists discover about the relationship between genes and DNA? Copyright Pearson Prentice Hall Copyright Pearson Prentice Hall 12–1 DNA 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. Slide 18 of 37 Copyright Pearson Prentice Hall End Show 12–1 DNA 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. Slide 19 of 37 Copyright Pearson Prentice Hall End Show 12–1 DNA Bacteriophages A virus that infects bacteria is known as a bacteriophage. Bacteriophages are composed of a DNA or RNA core and a protein coat. Slide 20 of 37 Copyright Pearson Prentice Hall End Show 12–1 DNA 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. Slide 21 of 37 Copyright Pearson Prentice Hall End Show 12–1 DNA 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). Slide 22 of 37 Copyright Pearson Prentice Hall End Show The Hershey-Chase Experiment If 35S 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 Copyright Pearson Prentice Hall No radioactivity inside bacterium 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 Copyright Pearson Prentice Hall Radioactivity inside bacterium 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. Copyright Pearson Prentice Hall What is the overall structure of the DNA molecule? Copyright Pearson Prentice Hall 12–1 DNA The Components and Structure of DNA Erwin Chargaff discovered that: • The percentages of guanine [G] and cytosine [C] bases are almost equal in any sample of DNA. • The percentages of adenine [A] and thymine [T] bases are almost equal in any sample of DNA. Slide 27 of 37 Copyright Pearson Prentice Hall End Show 12–1 DNA The Components and Structure of DNA Rosalind Franklin used X-ray diffraction to get information about the structure of DNA. She aimed an X-ray beam at concentrated DNA samples and recorded the scattering pattern of the X-rays on film. Slide 28 of 37 Copyright Pearson Prentice Hall End Show 12–1 DNA The Components and Structure of DNA 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. Slide 29 of 37 Copyright Pearson Prentice Hall End Show 12–1 DNA DNA: Double Helix Slide 30 of 37 Copyright Pearson Prentice Hall End Show 12–1 DNA 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. Slide 31 of 37 Copyright Pearson Prentice Hall End Show 12–1 DNA The Components and Structure of DNA The Components and Structure of DNA DNA is made up of nucleotides. A nucleotide is a monomer of nucleic acids made up of a five-carbon sugar called deoxyribose, a phosphate group, and a nitrogenous base. Slide 32 of 37 Copyright Pearson Prentice Hall End Show 12–1 DNA How do the 3 molecules join to form a nucleotide? Slide 33 of 37 End Show 12–1 DNA The Components and Structure of DNA There are four kinds of bases in in DNA: • adenine • guanine • cytosine • thymine Slide 34 of 37 Copyright Pearson Prentice Hall End Show 12–1 DNA Adenine Nucleotide Slide 35 of 37 End Show 12–1 DNA Thymine Nucleotide Slide 36 of 37 End Show 12–1 DNA Guanine Nucleotide Slide 37 of 37 End Show 12–1 DNA Cytosine Nucleotide Slide 38 of 37 End Show Copyright Pearson Prentice Hall 12–1 DNA 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. Slide 40 of 37 Copyright Pearson Prentice Hall End Show Paper Lab: Joining Nucleotides of DNA 12–1 Click to Launch: Continue to: - or - Slide 43 of 37 End Show Copyright Pearson Prentice Hall 12–1 Avery and other scientists discovered that a. DNA is found in a protein coat. b. DNA stores and transmits genetic information from one generation to the next. c. transformation does not affect bacteria. d. proteins transmit genetic information from one generation to the next. Slide 44 of 37 End Show Copyright Pearson Prentice Hall 12–1 The Hershey-Chase experiment was based on the fact that a. DNA has both sulfur and phosphorus in its structure. b. protein has both sulfur and phosphorus in its structure. c. both DNA and protein have no phosphorus or sulfur in their structure. d. DNA has only phosphorus, while protein has only sulfur in its structure. Slide 45 of 37 End Show Copyright Pearson Prentice Hall 12–1 DNA is a long molecule made of monomers called a. nucleotides. b. purines. c. pyrimidines. d. sugars. Slide 46 of 37 End Show Copyright Pearson Prentice Hall 12–1 Chargaff's rules state that the number of guanine nucleotides must equal the number of a. cytosine nucleotides. b. adenine nucleotides. c. thymine nucleotides. d. thymine plus adenine nucleotides. Slide 47 of 37 End Show Copyright Pearson Prentice Hall 12–1 In DNA, the following base pairs occur: a. A with C, and G with T. b. A with T, and C with G. c. A with G, and C with T. d. A with T, and C with T. Slide 48 of 37 End Show Copyright Pearson Prentice Hall END OF SECTION