DNA

By teclado777

  • Discovery of Structure of Nucleic Acids

    Discovery of Structure of Nucleic Acids
    Friederich Miescher a swiss physician and biologist, at the age of 24 years old, he discovers the genetics material from white blood cell nuclei. He noted it had an acidc nature and called it nuclein.

  • Levene's Tetranucleotide

    Levene's Tetranucleotide
    Levene proposed that there were four nucleotides per molecule.
    DNA could not store the genetic code because it was chemically far too simple.

  • Discovery of DNA Components

    Discovery of DNA Components
    Phoebus Leven (1869-1940).
    He determined the component of DNA: adenine, guanine, thymine, cytosine, deoxyribose phosphate.
    And he defined phosphate-sugar-base units called nucleotides.

  • Griffith Experiments

    Griffith Experiments
    Fedderick Griffith (1879-1941).
    He studied the epidemiology and pathology of two strains of Streptococcus pneumoniai.
    In January 1928 reported the first widely acceped demostrations of bacterial transformation.
    He used two strains of Streptococcus: Typs S: virulent (deadly) and Type R: non-virulent (harmless).

  • Avery, MacLeod and McCarty

    Avery, MacLeod and McCarty
    They determined the cause of the transformation in Griffith's experiment.
    They took live R and heat-treated S and mixed it with one of two enzymes: "proteases" which destroys protein, and DNase which destroys DNA

  • Watson and Crick Inside-Out Double Helix

    Watson and Crick Inside-Out Double Helix
    Watson and Crick wrote a paper in which they described DNA as a doible helix with sugars and phosphates at the center and the nucelobases facing the outside.
    This model was quickly shown to be incorrect and in fact it made no chemical sense.

  • Hershey-Chase Experiments

    Hershey-Chase Experiments
    Alfred Hershey (1908-1997) and Matha Chase (1927-2003) Americans geneticists.
    They used a bacterial cell and then they took bacteriophages labeled one of two ways. Either with radioactive sulfure, and that allowed them to follow the proteins in the phage, or they used radioactive DNA to follow the movement of DNA during the infection.

  • Conclusions of Hershey and Chase

    Conclusions of Hershey and Chase
    Hershey and Chase concluded that DNA, not protein, was the genetic material.
    A protective protein coat was formed around the bacteriophage, but the interlan DNA is what conferred its ability to produce progeny inside bacteria.

  • So, it's the DNA

    So, it's the DNA
    The race was on to determine the structure of DNA in cells and to determine how it codes for proteins and how it replicates.
    The problem: DNA exist in two forms: A form (dry form) and B form (wet form, as DNA exists in cells)

  • Pauling's Triple Helix

    Pauling's Triple Helix
    Linus Pauling and Robert Corey proposed a triple helix structure for DNA.

  • Counting Nucleobases

    Counting Nucleobases
    Erwin Chargaff (1905-2002) Australian Biochemist.
    Used paper of chromatography and UV spectroscopy to examine the abundanco of nucleobases and he started to notice something very odd.

  • Chargaff's Rules

    Chargaff's Rules
    When Chargaff began to measure the four bases: adenine, thymine, cytosine, and guanine. From different organisms, he found that the amount of adenine and thymine were always in balance with each other, and the amount of cytosine and guanine were always in balance with each other.

  • Rosalind Franklin's Photo 51

    Rosalind Franklin's Photo 51
    Rosalind Franklin took a lot of photos of the B form of DNA. She figured out how to see the wet form in cells. They call it photo 51. The photo is perfect because it shows very clearly the x in the middle that is the sign of a double helix.
    She didn't want to publish it because she wasn't sure about her calculation, but, somehow, Maurice Wilkins got the photo 51 and get it to Watson and crick in cambrige. When they saw the image, they knew what it meant.