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Genes and Transformation: The Key Role of DNA

Explore the fascinating world of genes and DNA through the experiments of Griffith, Avery, and Hershey-Chase, and discover how DNA is the genetic material responsible for transformation.

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Genes and Transformation: The Key Role of DNA

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  1. Chapter 12 DNA & RNA

  2. Interest Grabber Section 12-1 • Order! Order! • Genes are made of DNA, a large, complex molecule. DNA is composed of individual units called nucleotides. Three of these units form a code. The order, or sequence, of a code and the type of code determine the meaning of the message. 1. On a sheet of paper, write the word cats. List the letters or units that make up the word cats. 2. Try rearranging the units to form other words. Remember that eachnew word can have only three units. Write each word on your paper, and then add a definition for each word. 3. Did any of the codes you formed have the same meaning? 4. How do you think changing the order of the nucleotides in the DNA codon changes the codon’s message?

  3. I.DNA • A. Griffith & Transformation • Frederick Griffith was trying to figure out how bacteria made people sick-how they cause a certain type of pneumonia. • He isolated 2 strains(types) from mice-both cultured well,but only one caused pneumonia.The culture of the disease causing bacteria were __________________colonies while the other was rough. smooth

  4. 1-Griffith’s experiments (1928) • Mice injected w/ disease –causing strain got sick and died and nothing happened if injected w/other strain…He wondered if the disease-causing type made a toxin…? • So he took some of disease strain and heated to kill bacteria and then injected into mice….mice survived suggesting it was not a toxin producing disease

  5. Figure 12–2 Griffith’s Experiment Section 12-1 Heat-killed, disease-causing bacteria (smooth colonies) Harmless bacteria (rough colonies) Harmless bacteria (rough colonies) Control(no growth) Heat-killed, disease-causing bacteria (smooth colonies) Disease-causing bacteria (smooth colonies) Dies of pneumonia Dies of pneumonia Lives Lives Live, disease-causingbacteria (smooth colonies)

  6. Figure 12–2 Griffith’s Experiment Section 12-1 Heat-killed, disease-causing bacteria (smooth colonies) Harmless bacteria (rough colonies) Harmless bacteria (rough colonies) Control(no growth) Heat-killed, disease-causing bacteria (smooth colonies) Disease-causing bacteria (smooth colonies) Dies of pneumonia Dies of pneumonia Lives Lives Live, disease-causingbacteria (smooth colonies)

  7. 2-Transformation • He mixed his heat –killed w/ live harmless bacteria and injected into mice…..________________________ • Somehow the disease –causing strain passed their disease capacity to harmless bacteria….. disease –causing strain found in lungs • He called this changing of one bacteria by the genes of another _____________________....Thus a factor(gene) from heat killed disease –causing strain was passed on. Mice developed pneumonia transformation

  8. B. Avery & DNA • Team of scientists lead by Avery in 1944 repeated Griffith’s experiment in order to determine which molecule was responsible for the transformation. • They made an extract from the heat-killed bacteria and treated it w/enzymes that kill proteins,lipids and other molecules,inc. RNA

  9. Avery cont’d transformation • ____________________still occurred so the above molecules were not responsible for transformation • They repeated the experiment but used enzymes that kill____________, stopping transformation…. • Therefore ________caused the transformation and thus stores and transmits genetic info DNA DNA

  10. C. The Hershey –Chase Experiment • 1952-Alfred Hershey and Martha Chase studied viruses-disease-causing particles smaller than a cell. • ______________________-virus that infects bacteria.They have a DNA or RNA core and a protein coat…They attach to the surface of a bacterium and inject genetic info into cell.The viral genes act to produce many new bacteriophages and eventually destroy bacterial cell,w/_____________bursting out. viruses bacteriophage

  11. They grew viruses in cultures containing _________________________________,mixed them w/bacteria and waited a few min. for viruses to inject genetic material. • Then they separated the bacteria from the viruses and tested bacteria for radioactive marker…..nearly all the radioactivity was P-32-found in _________----thus concluding it was the genetic material was DNA ! Radioactive markers DNA

  12. Figure 12–4 Hershey-Chase Experiment Section 12-1 Bacteriophage with phosphorus-32 in DNA Phage infectsbacterium Radioactivity inside bacterium Bacteriophage with sulfur-35 in protein coat Phage infectsbacterium No radioactivity inside bacterium

  13. Figure 12–4 Hershey-Chase Experiment Section 12-1 Bacteriophage with phosphorus-32 in DNA Phage infectsbacterium Radioactivity inside bacterium Bacteriophage with sulfur-35 in protein coat Phage infectsbacterium No radioactivity inside bacterium

  14. Figure 12–4 Hershey-Chase Experiment Section 12-1 Bacteriophage with phosphorus-32 in DNA Phage infectsbacterium Radioactivity inside bacterium Bacteriophage with sulfur-35 in protein coat Phage infectsbacterium No radioactivity inside bacterium

  15. D. The Components and Structure of DNA • Scientists questioned how the DNA molecule could do three things 1)carry info from 1 generation to the next 2)putting that info to work and 3)could be easily copied • DNA is a long molecule made of units called ___________________________________________- nucleotides

  16. The nucleotide is made of 3 basic parts:______________________(sugar), a phosphate group and a_________________________________ deoxyribose Nitrogenous base

  17. 2 nitrogenous bases are purines(have 2 rings):___________________________(A)and_______(G) • 2 other nitrogenous bases are pyrimidines (have 1 ring):____________________(C)and ____________________________(T) Cytosine and thymine Adenine ,guanine --backbone made by sugar and phosphate w/ bases sticking out sideways

  18. Figure 12–5 DNA Nucleotides Section 12-1 Purines Pyrimidines Adenine Guanine Cytosine Thymine Phosphate group Deoxyribose

  19. 1-_______________________Rules-discovered that %’s of Cytosine and guanine were almost equal in DNA and the same was true for adenine and thymine….Thus A pairs w/T and C w/ G-BASE PAIRING Chargaff’s Rules

  20. Percentage of Bases in Four Organisms Section 12-1 Source of DNA A T G C Streptococcus 29.8 31.6 20.5 18.0 Yeast 31.3 32.9 18.7 17.1 Herring 27.8 27.5 22.2 22.6 Human 30.9 29.4 19.9 19.8

  21. 2- X-ray evidence-1950’s –Rosalind Franklin used X-ray diffraction to learn about DNA structure----The scattered X pattern seen begins to show the __________-partial TWISTED STRUCTURE of DNA helix

  22. 3---Double helix_ • Watson and Crick -2 strands wound around each other---like the twisted ladder or spiral staircase • Strands held together by H-bonds

  23. Figure 12–7 Structure of DNA Section 12-1 Nucleotide Hydrogen bonds Sugar-phosphate backbone Key Adenine (A) Thymine (T) Cytosine (C) Guanine (G)

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