Science isn't pretty - there's a lot at stake and things can get ugly. So it was with the discovery of DNA, for which only Watson and Crick get credit. But not on my watch. CORRECTION: Francis Crick was NOT an American as shown in the caption beneath his photo. He was born in Northamptonshire, England. I made the correction using the YouTube annotations feature, but not all devices show annotations. Want more? Subscribe: null FB Page: https://www.facebook.com/ThePenguinProf Twitter: https://twitter.com/penguinprof Web: http://www.penguinprof.com/ VIDEO DETAILS: DNA: The Backstory What gets passed down from generation to generation? What does the molecule look like? How does it work? How does it replicate itself? Discovery of Nucleic Acids Friedrich Miescher (1869) Isolated the genetic material from white blood cell nuclei. He noted it had an acidic nature and called it nuclein Discovery of DNA Components Phoebus Levene Determined the components of DNA: adenine, guanine, thymine, cytosine, deoxyribose phosphate defined phosphate-sugar-base units called nucleotides Levene's Tetranucleotide (1910) Levene proposed that there were four nucleotides per molecule Said DNA could not store the genetic code because it was chemically far too simple Frederick Griffith and his Transformation Experiment Studied the epidemiology and pathology of 2 strains of Streptococcus pneumoniae In January 1928 reported the first widely accepted demonstrations of bacterial transformation Griffith used two strains of Streptococcus: Type S: virulent (deadly) Type R: non-virulent (harmless) Observed bacterial transformation but did not understand the mechanism Avery, MacLeod and McCarty 1944 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: a protease (destroys protein) a DNAse (destroys DNA) Published in the Journal of Experimental Medicine February, 1944 Studies on the Chemical Nature of the Substance Inducing Transformation of Pneumococcal Types: Induction of Transformation by a Deoxyribonucleic Acid Fraction Isolated from Pneumococcus Type III DNA not protein was responsible for the bacterial transformation Griffith observed! DNA Discovery Timeline Erwin Chargoff was Counting Nucleobasesm in 1952 Used paper chromatography and UV spectroscopy to examine the abundance of the nucleobases and he started to notice something VERY odd... Came to be known as "Chargoff's Rules" Amounts of Adenine = Amounts of Thymine Amounts of Cytosine = Amounts of Guanine ALWAYS in EVERY SPECIES!!! Hershey-Chase Experiments (1952) Used phages and radiolabeled phosphorus and sulfur Hershey and Chase concluded that DNA, not protein, was the genetic material. A protective protein coat was formed around the bacteriophage, but the internal DNA is what conferred its ability to produce progeny inside bacteria 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 exists in two forms A form (dry form) B form (wet form, as DNA exists in cells) In 1951, Watson and Crick wrote a paper in which they described DNA as a double helix with sugars and phosphates at the center and the nucleobases facing the outside This model was quickly shown to be incorrect and in fact it made no chemical sense Triple Helix? Linus Pauling and Robert Corey proposed a triple helix structure for DNA Eureka James Watson and Francis Crick 1953 BUT now the story of thieves and lies... Francis Crick, James Watson, Maurice Wilkins, Rosalind Franklin Papers in sequence in Nature April 25, 1953 (THREE papers, not 1) DNA Discovery Timeline So now we have it. DNA is a Double-Stranded Helix The backbone is made of sugar (deoxyribose) and phosphate groups Hydrogen bonds between the nucleobases: A-T and G-C The sequence of nucleobases codifies the amino acid sequence of a protein. Strings of base pairs that code for a product are called genes