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Lesson Overview
  12.1 Identifying the
  Substance of Genes
Lesson Overview         Identifying the Substance of Genes


  THINK ABOUT IT
       How do genes work?

       To answer that question, the first thing you need to know is what genes
       are made of.

       How would you go about figuring out what molecule or molecules go into
       making a gene?
Lesson Overview          Identifying the Substance of Genes


  Bacterial Transformation
     What clues did bacterial transformation yield about the gene?
Lesson Overview          Identifying the Substance of Genes


  Bacterial Transformation
     What clues did bacterial transformation yield about the gene?

     By observing bacterial transformation, Avery and other scientists
     discovered that the nucleic acid DNA stores and transmits genetic
     information from one generation of bacteria to the next.
Lesson Overview           Identifying the Substance of Genes


  Bacterial Transformation
     To truly understand genetics, scientists realized they had to discover the
     chemical nature of the gene.

     If the molecule that carries genetic information could be identified, it might
     be possible to understand how genes control the inherited characteristics
     of living things.

     The discovery of the chemical nature of the gene began in 1928 with British
     scientist Frederick Griffith, who was trying to figure out how certain types of
     bacteria produce pneumonia.
Lesson Overview          Identifying the Substance of Genes


  Griffith’s Experiments
       Griffith isolated two different strains of the same bacterial species.

       Both strains grew very well in culture plates in Griffith’s lab, but only
       one of the strains caused pneumonia.
Lesson Overview         Identifying the Substance of Genes


  Griffith’s Experiments
       The disease-causing bacteria (S strain) grew into smooth colonies on
       culture plates, whereas the harmless bacteria
       (R strain) produced colonies with rough edges.
Lesson Overview         Identifying the Substance of Genes


  Griffith’s Experiments
       When Griffith injected mice with disease-causing bacteria, the
       mice developed pneumonia and died.

       When he injected mice with harmless bacteria, the mice stayed
       healthy.

       Perhaps the S-strain bacteria produced a toxin that made the mice sick?
       To find out, Griffith ran a series of experiments.
Lesson Overview           Identifying the Substance of Genes


  Griffith’s Experiments
       First, Griffith took a culture of the S strain, heated the cells to kill them,
       and then injected the heat-killed bacteria into laboratory mice.

       The mice survived, suggesting that the cause of pneumonia was not a
       toxin from these disease-causing bacteria.
Lesson Overview          Identifying the Substance of Genes


  Griffith’s Experiments
      In Griffith’s next experiment, he mixed the heat-killed, S-strain bacteria
      with live, harmless bacteria from the R strain and injected the mixture
      into laboratory mice.

      The injected mice developed pneumonia, and many died.
Lesson Overview          Identifying the Substance of Genes


  Griffith’s Experiments
      The lungs of these mice were filled with the disease-causing bacteria.
      How could that happen if the S strain cells were dead?
Lesson Overview         Identifying the Substance of Genes


  Transformation
       Griffith reasoned that some chemical factor that could change harmless
       bacteria into disease-causing bacteria was transferred from the heat-
       killed cells of the S strain into the live cells of the R strain.
Lesson Overview         Identifying the Substance of Genes


  Transformation
       He called this process transformation, because one type of bacteria
       had been changed permanently into another.
Lesson Overview          Identifying the Substance of Genes


  Transformation
       Because the ability to cause disease was inherited by the offspring of
       the transformed bacteria, Griffith concluded that the transforming factor
       had to be a gene.
Lesson Overview          Identifying the Substance of Genes


  The Molecular Cause of Transformation
       A group of scientists at the Rockefeller Institute in New York, led by the
       Canadian biologist Oswald Avery, wanted to determine which molecule
       in the heat-killed bacteria was most important for transformation.
Lesson Overview          Identifying the Substance of Genes


  The Molecular Cause of Transformation
       Avery and his team extracted a mixture of various molecules from the
       heat-killed bacteria and treated this mixture with enzymes that
       destroyed proteins, lipids, carbohydrates, and some other molecules,
       including the nucleic acid RNA.

       Transformation still occurred.
Lesson Overview         Identifying the Substance of Genes


  The Molecular Cause of Transformation
       Avery’s team repeated the experiment using enzymes that would break
       down DNA.

       When they destroyed the DNA in the mixture, transformation did not
       occur.

       Therefore, DNA was the transforming factor.
Lesson Overview          Identifying the Substance of Genes


  Bacterial Viruses
     What role did bacterial viruses play in identifying genetic material?
Lesson Overview           Identifying the Substance of Genes


  Bacterial Viruses
     What role did bacterial viruses play in identifying genetic material?

     Hershey and Chase’s experiment with bacteriophages confirmed Avery’s
     results, convincing many scientists that DNA was the genetic material
     found in genes—not just in viruses and bacteria, but in all living cells.
Lesson Overview          Identifying the Substance of Genes


  Bacterial Viruses
     Several different scientists repeated Avery’s experiments. Alfred Hershey
     and Martha Chase performed the most important of the experiments
     relating to Avery’s discovery.

     Hershey and Chase studied viruses—nonliving particles that can
     infect living cells.
Lesson Overview         Identifying the Substance of Genes


  Bacteriophages
       The kind of virus that infects bacteria is known as a bacteriophage,
       which means “bacteria eater.”

       A typical bacteriophage is shown.
Lesson Overview         Identifying the Substance of Genes


  Bacteriophages
       When a bacteriophage enters a bacterium, it attaches to the
       surface of the bacterial cell and injects its genetic information into
       it.
Lesson Overview        Identifying the Substance of Genes


  Bacteriophages
       The viral genes act to produce many new bacteriophages, which
       gradually destroy the bacterium.

       When the cell splits open, hundreds of new viruses burst out.
Lesson Overview          Identifying the Substance of Genes


  The Hershey-Chase Experiment
      American scientists Alfred Hershey and Martha Chase studied a bacteriophage
      that was composed of a DNA core and a protein coat.

      They wanted to determine which part of the virus—the protein coat or the
      DNA core—entered the bacterial celll
Lesson Overview           Identifying the Substance of Genes


  The Hershey-Chase Experiment
      Their results would either support or disprove Avery’s finding that genes were
      made of DNA.
Lesson Overview         Identifying the Substance of Genes


  The Hershey-Chase Experiment
       Hershey and Chase grew viruses in cultures containing radioactive
       isotopes of phosphorus-32 (P-32) sulfur-35 (S-35)
Lesson Overview         Identifying the Substance of Genes


  The Hershey-Chase Experiment
       Since proteins contain almost no phosphorus and DNA contains no
       sulfur, these radioactive substances could be used as markers, enabling
       the scientists to tell which molecules actually entered the bacteria and
       carried the genetic information of the virus.
Lesson Overview          Identifying the Substance of Genes


  The Hershey-Chase Experiment
       If they found radioactivity from S-35 in the bacteria, it would mean that
       the virus’s protein coat had been injected into the bacteria.

       If they found P-32 then the DNA core had been injected.
Lesson Overview         Identifying the Substance of Genes


  The Hershey-Chase Experiment
       The two scientists mixed the marked viruses with bacterial cells, waited
       a few minutes for the viruses to inject their genetic material, and then
       tested the bacteria for radioactivity.
Lesson Overview         Identifying the Substance of Genes


  The Hershey-Chase Experiment
       Nearly all the radioactivity in the bacteria was from phosphorus P-32 ,
       the marker found in DNA.

       Hershey and Chase concluded that the genetic material of the
       bacteriophage was DNA, not protein.
Lesson Overview          Identifying the Substance of Genes


  The Role of DNA
     What is the role of DNA in heredity?
Lesson Overview          Identifying the Substance of Genes


  The Role of DNA
     What is the role of DNA in heredity?

     The DNA that makes up genes must be capable of storing, copying, and
     transmitting the genetic information in a cell.
Lesson Overview          Identifying the Substance of Genes


  The Role of DNA
     The DNA that makes up genes must be capable of storing, copying,
     and transmitting the genetic information in a cell.

     These three functions are analogous to the way in which you might share a
     treasured book, as pictured in the figure.
Lesson Overview         Identifying the Substance of Genes


  Storing Information
       The foremost job of DNA, as the molecule of heredity, is to store
       information.

       Genes control patterns of development, which means that the
       instructions that cause a single cell to develop into an oak tree, a sea
       urchin, or a dog must somehow be written into the DNA of each of these
       organisms.
Lesson Overview         Identifying the Substance of Genes


  Copying Information
       Before a cell divides, it must make a complete copy of every one of its
       genes, similar to the way that a book is copied.
Lesson Overview         Identifying the Substance of Genes


  Copying Information
       To many scientists, the most puzzling aspect of DNA was how it could
       be copied.

       Once the structure of the DNA molecule was discovered, a copying
       mechanism for the genetic material was soon put forward.
Lesson Overview          Identifying the Substance of Genes


  Transmitting Information
       When a cell divides, each daughter cell must receive a complete copy of
       the genetic information.

       Careful sorting is especially important during the formation of
       reproductive cells in meiosis.

       The loss of any DNA during meiosis might mean a loss of valuable
       genetic information from one generation to the next.

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Powerpoint Chapter 12.1

  • 1. Lesson Overview 12.1 Identifying the Substance of Genes
  • 2. Lesson Overview Identifying the Substance of Genes THINK ABOUT IT How do genes work? To answer that question, the first thing you need to know is what genes are made of. How would you go about figuring out what molecule or molecules go into making a gene?
  • 3. Lesson Overview Identifying the Substance of Genes Bacterial Transformation What clues did bacterial transformation yield about the gene?
  • 4. Lesson Overview Identifying the Substance of Genes Bacterial Transformation What clues did bacterial transformation yield about the gene? By observing bacterial transformation, Avery and other scientists discovered that the nucleic acid DNA stores and transmits genetic information from one generation of bacteria to the next.
  • 5. Lesson Overview Identifying the Substance of Genes Bacterial Transformation To truly understand genetics, scientists realized they had to discover the chemical nature of the gene. If the molecule that carries genetic information could be identified, it might be possible to understand how genes control the inherited characteristics of living things. The discovery of the chemical nature of the gene began in 1928 with British scientist Frederick Griffith, who was trying to figure out how certain types of bacteria produce pneumonia.
  • 6. Lesson Overview Identifying the Substance of Genes Griffith’s Experiments Griffith isolated two different strains of the same bacterial species. Both strains grew very well in culture plates in Griffith’s lab, but only one of the strains caused pneumonia.
  • 7. Lesson Overview Identifying the Substance of Genes Griffith’s Experiments The disease-causing bacteria (S strain) grew into smooth colonies on culture plates, whereas the harmless bacteria (R strain) produced colonies with rough edges.
  • 8. Lesson Overview Identifying the Substance of Genes Griffith’s Experiments When Griffith injected mice with disease-causing bacteria, the mice developed pneumonia and died. When he injected mice with harmless bacteria, the mice stayed healthy. Perhaps the S-strain bacteria produced a toxin that made the mice sick? To find out, Griffith ran a series of experiments.
  • 9. Lesson Overview Identifying the Substance of Genes Griffith’s Experiments First, Griffith took a culture of the S strain, heated the cells to kill them, and then injected the heat-killed bacteria into laboratory mice. The mice survived, suggesting that the cause of pneumonia was not a toxin from these disease-causing bacteria.
  • 10. Lesson Overview Identifying the Substance of Genes Griffith’s Experiments In Griffith’s next experiment, he mixed the heat-killed, S-strain bacteria with live, harmless bacteria from the R strain and injected the mixture into laboratory mice. The injected mice developed pneumonia, and many died.
  • 11. Lesson Overview Identifying the Substance of Genes Griffith’s Experiments The lungs of these mice were filled with the disease-causing bacteria. How could that happen if the S strain cells were dead?
  • 12. Lesson Overview Identifying the Substance of Genes Transformation Griffith reasoned that some chemical factor that could change harmless bacteria into disease-causing bacteria was transferred from the heat- killed cells of the S strain into the live cells of the R strain.
  • 13. Lesson Overview Identifying the Substance of Genes Transformation He called this process transformation, because one type of bacteria had been changed permanently into another.
  • 14. Lesson Overview Identifying the Substance of Genes Transformation Because the ability to cause disease was inherited by the offspring of the transformed bacteria, Griffith concluded that the transforming factor had to be a gene.
  • 15. Lesson Overview Identifying the Substance of Genes The Molecular Cause of Transformation A group of scientists at the Rockefeller Institute in New York, led by the Canadian biologist Oswald Avery, wanted to determine which molecule in the heat-killed bacteria was most important for transformation.
  • 16. Lesson Overview Identifying the Substance of Genes The Molecular Cause of Transformation Avery and his team extracted a mixture of various molecules from the heat-killed bacteria and treated this mixture with enzymes that destroyed proteins, lipids, carbohydrates, and some other molecules, including the nucleic acid RNA. Transformation still occurred.
  • 17. Lesson Overview Identifying the Substance of Genes The Molecular Cause of Transformation Avery’s team repeated the experiment using enzymes that would break down DNA. When they destroyed the DNA in the mixture, transformation did not occur. Therefore, DNA was the transforming factor.
  • 18. Lesson Overview Identifying the Substance of Genes Bacterial Viruses What role did bacterial viruses play in identifying genetic material?
  • 19. Lesson Overview Identifying the Substance of Genes Bacterial Viruses What role did bacterial viruses play in identifying genetic material? Hershey and Chase’s experiment with bacteriophages confirmed Avery’s results, convincing many scientists that DNA was the genetic material found in genes—not just in viruses and bacteria, but in all living cells.
  • 20. Lesson Overview Identifying the Substance of Genes Bacterial Viruses Several different scientists repeated Avery’s experiments. Alfred Hershey and Martha Chase performed the most important of the experiments relating to Avery’s discovery. Hershey and Chase studied viruses—nonliving particles that can infect living cells.
  • 21. Lesson Overview Identifying the Substance of Genes Bacteriophages The kind of virus that infects bacteria is known as a bacteriophage, which means “bacteria eater.” A typical bacteriophage is shown.
  • 22. Lesson Overview Identifying the Substance of Genes Bacteriophages When a bacteriophage enters a bacterium, it attaches to the surface of the bacterial cell and injects its genetic information into it.
  • 23. Lesson Overview Identifying the Substance of Genes Bacteriophages The viral genes act to produce many new bacteriophages, which gradually destroy the bacterium. When the cell splits open, hundreds of new viruses burst out.
  • 24. Lesson Overview Identifying the Substance of Genes The Hershey-Chase Experiment American scientists Alfred Hershey and Martha Chase studied a bacteriophage that was composed of a DNA core and a protein coat. They wanted to determine which part of the virus—the protein coat or the DNA core—entered the bacterial celll
  • 25. Lesson Overview Identifying the Substance of Genes The Hershey-Chase Experiment Their results would either support or disprove Avery’s finding that genes were made of DNA.
  • 26. Lesson Overview Identifying the Substance of Genes The Hershey-Chase Experiment Hershey and Chase grew viruses in cultures containing radioactive isotopes of phosphorus-32 (P-32) sulfur-35 (S-35)
  • 27. Lesson Overview Identifying the Substance of Genes The Hershey-Chase Experiment Since proteins contain almost no phosphorus and DNA contains no sulfur, these radioactive substances could be used as markers, enabling the scientists to tell which molecules actually entered the bacteria and carried the genetic information of the virus.
  • 28. Lesson Overview Identifying the Substance of Genes The Hershey-Chase Experiment If they found radioactivity from S-35 in the bacteria, it would mean that the virus’s protein coat had been injected into the bacteria. If they found P-32 then the DNA core had been injected.
  • 29. Lesson Overview Identifying the Substance of Genes The Hershey-Chase Experiment The two scientists mixed the marked viruses with bacterial cells, waited a few minutes for the viruses to inject their genetic material, and then tested the bacteria for radioactivity.
  • 30. Lesson Overview Identifying the Substance of Genes The Hershey-Chase Experiment Nearly all the radioactivity in the bacteria was from phosphorus P-32 , the marker found in DNA. Hershey and Chase concluded that the genetic material of the bacteriophage was DNA, not protein.
  • 31. Lesson Overview Identifying the Substance of Genes The Role of DNA What is the role of DNA in heredity?
  • 32. Lesson Overview Identifying the Substance of Genes The Role of DNA What is the role of DNA in heredity? The DNA that makes up genes must be capable of storing, copying, and transmitting the genetic information in a cell.
  • 33. Lesson Overview Identifying the Substance of Genes The Role of DNA The DNA that makes up genes must be capable of storing, copying, and transmitting the genetic information in a cell. These three functions are analogous to the way in which you might share a treasured book, as pictured in the figure.
  • 34. Lesson Overview Identifying the Substance of Genes Storing Information The foremost job of DNA, as the molecule of heredity, is to store information. Genes control patterns of development, which means that the instructions that cause a single cell to develop into an oak tree, a sea urchin, or a dog must somehow be written into the DNA of each of these organisms.
  • 35. Lesson Overview Identifying the Substance of Genes Copying Information Before a cell divides, it must make a complete copy of every one of its genes, similar to the way that a book is copied.
  • 36. Lesson Overview Identifying the Substance of Genes Copying Information To many scientists, the most puzzling aspect of DNA was how it could be copied. Once the structure of the DNA molecule was discovered, a copying mechanism for the genetic material was soon put forward.
  • 37. Lesson Overview Identifying the Substance of Genes Transmitting Information When a cell divides, each daughter cell must receive a complete copy of the genetic information. Careful sorting is especially important during the formation of reproductive cells in meiosis. The loss of any DNA during meiosis might mean a loss of valuable genetic information from one generation to the next.