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  • 1. DNA: Molecule of Heredity
  • 2. Genes Are Made of DNA
    • Known since the late 1800s:
        • Heritable information is carried in discrete units called genes
        • Genes are parts of structures called chromosomes
        • Chromosomes are made of deoxyribonucleic acid ( DNA ) and protein
  • 3. Genes Are Made of DNA
    • Transformed bacteria revealed the link between genes and DNA
    • F. Griffith worked with two strains of Streptococcus pneumoniae bacteria
      • S strain caused pneumonia when injected into mice, killing them
      • R strain did not cause pneumonia when injected
  • 4. Transformed Bacteria Mouse injected w/bacteria Results Conclusions R strain does not cause pneumonia S strain does cause pneumonia Heat-killed S strain does not cause pneumonia Substance from heat-killed S strain can transform harmless R strain into deadly S strain
  • 5. Genes Are Made of DNA
    • Deductions from Griffith’s experiment (1920s)
      • Living safe bacteria (R strain) were changed by something in the dead (but normally disease-causing) S strain
      • The living R strain bacteria were transformed by genetic material released by the S strain
  • 6. Genes Are Made of DNA
    • Later findings by Avery, MacLeod, and McCarty (1940s)
      • The transforming molecule from the S strain was DNA
  • 7.  
  • 8.  
  • 9. DNA Is Composed of Four Nucleotides
    • DNA is made of chains of small subunits called nucleotides
    • Each nucleotide has three components:
        • Phosphate group
        • Deoxyribose sugar
        • One of four nitrogen-containing bases
          • Thymine Cytosine
          • Adenine Guanine
  • 10. DNA Is Composed of Four Nucleotides
    • Types of Nitrogen Bases…
    • Purines
    • 2 rings
    • A and G
    • Pyrimidines
    • 1 ring
    • T and C
  • 11. The Four Nucleotides of DNA DNA Thymine DNA Cytosine DNA Guanine DNA Adenine
  • 12. DNA Is Composed of Four Nucleotides
    • In 1940, biochemist E. Chargaff determined that:
      • In a DNA molecule, amounts of
        • A = T, G = C
      • “ Chargaff’s Rule”
  • 13. DNA Is a Double Helix
    • Rosalind Franklin and Maurice Wilkins studied DNA structure using X-ray scattering
  • 14. DNA Is a Double Helix
    • From X-ray diffraction patterns they deduced that DNA …
      • Is long and thin
      • Has a uniform diameter of 2 nanometers
      • Is helical, and is twisted like a corkscrew
      • Consists of repeating subunits
  • 15. DNA Is a Double Helix
    • James Watson and Francis Crick combined the X-ray data with bonding theory to deduce DNA structure:
      • DNA is made of two strands of nucleotides
      • The deoxyribose and phosphate portions make up the sugar-phosphate backbone
  • 16.  
  • 17. Please don’t admire Dr Watson…
    • He is "inherently gloomy about the prospect of Africa". –October 2007
    • To him, the real cause of Africa's woes is that black people are inherently less intelligent than other races. "All our social policies are based on the fact that their intelligence is the same as ours — whereas all the testing says not really,"
    • He hoped that everyone was equal, he continued, but "people who have to deal with black employees find this not true".
  • 18. Please don’t admire Dr Watson…
    • (Amount of melanin in the skin) was why black people and Latinos had reputations as lovers — something, he said, of which the English could not be accused. -2000
    • "Whenever you interview fat people, you feel bad because you know you're not going to hire them," -2000
    • In 1997, he even said a woman should be allowed to abort a fetus if tests had shown it would be a homosexual and the mother deemed this undesirable.
  • 19.
    • James Watson is AMERICAN. Not British. He was born in Chicago. Studied and researched in London but spent less that 5 years there.
    • He currently resides at Cold Spring Harbor Lab in Huntington, Long Island NY. He is currently suspended from the lab he founded due to his remarks. (Update 10/25/07…he just “retired”)
    • More quotes…
  • 20.
    • Watson has repeatedly supported genetic screening and genetic engineering in public lectures and interviews, arguing that stupidity is a disease and the "really stupid" bottom 10% of people should be cured
    • He has also suggested that beauty could be genetically engineered, saying "People say it would be terrible if we made all girls pretty. I think it would be great .”
  • 21. The Watson-Crick Model of DNA Structure Hydrogen bonds form between complementary bases Complementary base pairs hold the two DNA strands together DNA is a double helix of two nucleotide strands
  • 22. Hydrogen Bonds
    • Nitrogen-containing bases protrude inward from sugar-phosphate backbone
    • Hydrogen bonds hold certain nitrogenous base pairs together
      • A bonds with T, G bonds with C
      • Bonding bases called complementary base pairs
      • A and T bond with TWO Hydrogen bonds
      • G and C bond with THREE Hydro. bonds
  • 23. How Does DNA Encode Information?
    • How can a molecule with only 4 simple parts be the carrier of genetic information?
    • The key lies in the sequence , not number , of subunits
    • Within a DNA strand, the four types of bases can be arranged in any linear order, and this sequence is what encodes genetic information
  • 24. How Does DNA Encode Information?
    • The genetic code is analogous to languages, where small sets of letters combine in various ways to make up many different words
      • English has 26 letters
      • Hawaiian has 12 letters
      • The binary language of computers uses only 2 “letters” (0 and 1, or “on” and “off”)
  • 25. How Does DNA Encode Information?
    • The sequence of only four nucleotides can produce many different combinations
      • A 10 nucleotide sequence can code for greater than 1 million different combinations
  • 26. DNA Replication
    • All cells come from pre-existing cells
    • Cells reproduce by dividing in half
    • Each of two daughter cells gets an exact copy of parent cell’s genetic information
    • Duplication of the parent cell DNA is called replication
  • 27. DNA Replication
    • DNA replication begins when DNA helicases separate the two strands
      • Hydrogen bonds between bases are broken
    Parental DNA double helix New double helix with 1 old & 1 new strand Free Nucleotides
  • 28. DNA Replication
    • A second strand of new DNA is synthesized along each separated strand by DNA polymerases, which position free nucleotides across from complementary nucleotides
    Parental DNA double helix New double helix with 1 old & 1 new strand Free Nucleotides
  • 29. DNA Replication
    • The two resulting DNA molecules have one old parental strand and one new strand ( semiconservative replication )
  • 30. The Semiconservative Replication Model One DNA double helix Duplicated Chromosome Chromosome Daughter chromosomes half old , half new Both strands of original DNA serve as templates Sister Chromatids
  • 31. Replication Bubble Replication forks move in opposite directions Replication Forks Replication Bubble Parental Daughter DNA replication begins DNA replication progresses DNA replication completed
  • 32. Replication Details (1)
    • One strand replicated as continuous segment
    Other replicated in short segments (to be joined later by ligase) Replication Fork P P P P S S S S C o n t i n u o u s S e g m e n t e d Unzipping
  • 33. Replication Details (2)
  • 34. Replication Details (3)
    • Helicase unzips DNA
    • DNA polymerases add loose nucleotides to growing strands
    • DNA ligase connects short strands together
  • 35. Replication And Proofreading
    • During replication, DNA polymerase mismatches nucleotides once every 10,000 base pairs
    • DNA repair enzymes “proofread” each new daughter strand, replacing mismatched nucleotides
    • However…
  • 36. Mistakes Do Happen
    • DNA is damaged in a number of ways
    • Spontaneous chemical breakdown at body temperature
    • Certain chemicals (some components of cigarette smoke)
    • UV light from the sun causes DNA damage
      • DNA damage leads to uncontrollable cell division and skin cancer
  • 37. Types of Mutations
    • Point mutation - individual nucleotide in the DNA sequence is changed
    • Insertion mutation - one or more nucleotide pairs are inserted into the DNA double helix
    • Deletion mutation - one or more nucleotide pairs are removed from the double helix
  • 38.  
  • 39.  
  • 40.  
  • 41. Types of Mutations
    • Inversion - piece of DNA is cut out of a chromosome, turned around, and re-inserted into the gap
    • Translocation - chunk of DNA (often very large) is removed from one chromosome and attached to another
  • 42.  
  • 43.  
  • 44. The end