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End Show Slide 1 of 37 Copyright Pearson Prentice Hall Biology.

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1 End Show Slide 1 of 37 Copyright Pearson Prentice Hall Biology

2 End Show Slide 2 of Objectives What did scientists discover about the relationship between genes and DNA? What is the overall structure of the DNA molecule? Copyright Pearson Prentice Hall

3 End Show Slide 3 of 37 Copyright Pearson Prentice Hall 12–1 DNA

4 End Show 12–1 DNA Slide 4 of 37 Copyright Pearson Prentice Hall 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.

5 End Show 12–1 DNA Slide 5 of 37 Copyright Pearson Prentice Hall 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.

6 End Show 12–1 DNA Slide 6 of 37 Copyright Pearson Prentice Hall 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.

7 End Show 12–1 DNA Slide 7 of 37 Copyright Pearson Prentice Hall 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

8 End Show 12–1 DNA Slide 8 of 37 Copyright Pearson Prentice Hall 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

9 End Show 12–1 DNA Slide 9 of 37 Copyright Pearson Prentice Hall 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)

10 End Show 12–1 DNA Slide 10 of 37 Copyright Pearson Prentice Hall 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

11 End Show 12–1 DNA Slide 11 of 37 Copyright Pearson Prentice Hall 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.

12 End Show 12–1 DNA Slide 12 of 37 Copyright Pearson Prentice Hall 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.

13 End Show 12–1 DNA Slide 13 of 37 Copyright Pearson Prentice Hall Avery and DNA The enzymes destroyed proteins, lipids, carbohydrates, and other molecules, including the nucleic acid RNA. Transformation still occurred.

14 End Show 12–1 DNA Slide 14 of 37 Copyright Pearson Prentice Hall 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.

15 End Show 12–1 DNA Slide 15 of 37 Copyright Pearson Prentice Hall Avery and DNA What did scientists discover about the relationship between genes and DNA?

16 End Show 12–1 DNA Slide 16 of 37 Copyright Pearson Prentice Hall 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 End Show 12–1 DNA Slide 17 of 37 Copyright Pearson Prentice Hall The Hershey-Chase Experiment Alfred Hershey and Martha Chase studied viruses—nonliving particles smaller than a cell that can infect living organisms.

18 End Show 12–1 DNA Slide 18 of 37 Copyright Pearson Prentice Hall 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.

19 End Show 12–1 DNA Slide 19 of 37 Copyright Pearson Prentice Hall 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.

20 End Show 12–1 DNA Slide 20 of 37 Copyright Pearson Prentice Hall 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).

21 End Show 12–1 DNA Slide 21 of 37 Copyright Pearson Prentice Hall 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

22 End Show 12–1 DNA Slide 22 of 37 Copyright Pearson Prentice Hall 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

23 End Show 12–1 DNA Slide 23 of 37 Copyright Pearson Prentice Hall The Hershey-Chase Experiment Nearly all the radioactivity in the bacteria was from phosphorus ( 32 P). Hershey and Chase concluded that the genetic material of the bacteriophage was DNA, not protein.

24 End Show 12–1 DNA Slide 24 of 37 Copyright Pearson Prentice Hall The Components and Structure of DNA What is the overall structure of the DNA molecule?

25 End Show 12–1 DNA Slide 25 of 37 Copyright Pearson Prentice Hall 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.

26 End Show 12–1 DNA Slide 26 of 37 Copyright Pearson Prentice Hall The Components and Structure of DNA There are four kinds of bases in in DNA: adenine guanine cytosine thymine

27 End Show 12–1 DNA Slide 27 of 37 Copyright Pearson Prentice Hall 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.

28 End Show 12–1 DNA Slide 28 of 37 Copyright Pearson Prentice Hall The Components and Structure of DNA Chargaff's Rules 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.

29 End Show 12–1 DNA Slide 29 of 37 Copyright Pearson Prentice Hall The Components and Structure of DNA X-Ray Evidence 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.

30 End Show 12–1 DNA Slide 30 of 37 Copyright Pearson Prentice Hall 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.

31 End Show 12–1 DNA Slide 31 of 37 Copyright Pearson Prentice Hall The Components and Structure of DNA DNA Double Helix

32 End Show 12–1 DNA Slide 32 of 37 Copyright Pearson Prentice Hall 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.

33 End Show - or - Continue to: Click to Launch: Slide 33 of 37 Copyright Pearson Prentice Hall 12–1

34 End Show Slide 34 of 37 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.

35 End Show Slide 35 of 37 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.

36 End Show Slide 36 of 37 Copyright Pearson Prentice Hall 12–1 DNA is a long molecule made of monomers called a.nucleotides. b.purines. c.pyrimidines. d.sugars.

37 End Show Slide 37 of 37 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.

38 End Show Slide 38 of 37 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.

39 END OF SECTION


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