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12 1

DNA

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12 1

  1. 1. Chapter 12-1 DNA(deoxyribonucleic acid)
  2. 2. DNA function• Nucleic acid• Store and transmit hereditary information
  3. 3. Experimental Proof of DNA as Genetic Material...
  4. 4. 1) Griffith’s Transformation Experiments
  5. 5. 1) Griffith’s Transformation Experiments• What two strains of bacteria did Griffith use? – S (smooth) strain –cause pneumonia – R (rough) strain –harmless• What happened in the fourth experiment? – The mice died. There were live S strains found in the mice body.• What can be concluded from the experiment? – Cell components in the dead S strains transformed the live R strains to live S strains
  6. 6. 2) Oswald Avery experiment• The transforming factor is DNA
  7. 7. 3) The Hershey-Chase’s bacteriophages experiment• Bacteriophages – viruses that infect bacteria – consist of protein coat and a DNA or RNA core – inject their hereditary material into bacteria
  8. 8. 3) The Hershey-Chase’s bacteriophages experiment
  9. 9. virus particle virus particle labeled with 35S labeled with 32P• Radioactive Markers – Radioactive bacterial cell (cutaway view) isotope – 32P could only mark DNA – 35S could only mark protein coat label outside cell label inside cell
  10. 10. DNA• Made by nucleotide – 5-carbon sugar (deoxyribose) 5 – phosphate group 4 1 – nitrogenous bases 3 2 • purine (2 rings): adenine , guanine; • pyrimidine (1 ring): cytosine , thymine
  11. 11. 54 1 3 2
  12. 12. Purines PyrimidinesAdenine Guanine Cytosine Thymine 1 1 1 1 2 2 2 2 3 3 3 3 5 4 5 4 5 4 5 4 Phosphate group Deoxyribose
  13. 13. DNA Structure• Chargaff’s Rule : – Amount of adenine = amount of thymine, amount of guanine = amount of cytosine – A=T and G=C
  14. 14. DNA Structure• Rosalind Franklin – Used x-ray diffraction to examine DNA fibers – Concluded that DNA was helix Rosalind Franklins X-ray diffraction photograph of DNA, 1953 Photo: courtesy HarperCollins
  15. 15. DNA Structure• Watson and Crick’s model – DNA have two strands run in opposite directions – Strands are held together by hydrogen bonds – A binds with T and C with G – Molecule is a double helix Hydrogen bond
  16. 16. DNA Structure
  17. 17. Nucleotide Hydrogen bondsSugar-phosphate backbone Key Adenine (A) Thymine (T) Cytosine (C) Guanine (G)
  18. 18. James D. Watson Francis H. C. Crick Wilkins Rosalind Franklin
  19. 19. Questions:• 20% A in DNA strands, how many C ?• A=T=20%,• A+T+G+C=100%• G=C,• C=30%
  20. 20. The drawing below shows a short section of a DNAmolecule. What is labelled by I, II and III? I II III I II III A. 3′ end purine hydrogen bond B. 5′ end pyrimidine covalent bond C. 3′ end pyrimidine hydrogen bond D. 5′ end purine covalent bond

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  • FasihaKhan3

    Mar. 8, 2019

DNA

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