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Discovery of Nucleic Acids
Friedrich Miescher was a Swiss physician and biologist. From 1869 to 1895 he discovered the nucleic acids. He 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 was a Lithuanian-American Biochemist, in 1969 he discovered the DNA components, these were: adenine, guanine, thymine, cytosine and deoxyribose phosphate. Also, he defined phosphate-sugar-base units called nucleotides -
Levene's Tetranucleotide
Levene an idea, he proposed that there were four nucleotides per molecule.
Said that the DNA could not store the genetic code because it was chemically far too simple.
All this was his proposal for the DNA structure. -
Frederick Griffith and his Transformation Experiment
Frederick Griffith was born at 1879 and he finished his life at 1941, he was a British bacteriologist.
He studied the epidemiology and pathology of 2 strains of Streptococcus pneumonia.
In 1928, he discovered the first widely accepted demonstrations of bacterial transformation. For do that, Griffith used two strains of Streptococcus: The type S: virulent (was deadly), and the type R:non-virulent (was harmless).
He observed transformations on the batteries, but did not understand the mechanism. -
Experiment Frederick Griffith
The Griffith Experiment was conducted in 1928 by Frederick Griffith, a bacteriologist, he described the conversation of a non-patheogenic pneumococcal bacteria to a virulent strain. In this experiment, Griffith mixed the living non-virulent bacteria with a heat inactivated virulent form. -
Avery, Macleod and Mc CArty
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:
-The first, a protease that destroys the protein
-The second, a DNAse that destroys the DNA -
Journal of Experimental Medicine
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! -
Double Helix
In 1915, Watson and Crick wrote a paper wick they described DNA as a double helix with sugars and phosphates at the center and the nuclobases facing the outside.
This model was quickly shown to be incorrect -
Counting Nucleobases
Erwin Chargaff Austrian biochemist (1905 to 2002). He used paper chromatography and UV spectroscopy to examine the abundance of the nucleases, and he started to notice something very odd. -
Chargaff's rules
Came to be known as "Chargoff's Rules"
Amounts of Adenine = Amounts of Thymine
Amounts of Cytosine = Amounts of Guanine
Unfortunately, Chargaff did not realize the importance of these findings; he did however share his discovery with Watson and Crick at Cambridge in 1952. -
Hershey-Chase Experiments
Used phages and radio labeled 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. -
Hershley-Chase Conclutions
Hershley had arrived to the conclusion that DNA was genetic material. -
Eureka
James Watson and Francis Crick, at 1953 more or less, when Rosalind Franklin takes photo 51, he sends it to his king's college London. The same, makes it to reach James Watson and Francis who thanks to the photo, just discover the entire structure of DNA and end up being credited with the discovery. -
So it's the DNA
The race was on to determinate the structure of DNA in cells and to determinate how it codes for proteins and how it replicates. The problem was that the DNA exists in two forms:
-A form, the dry one
-B form, the wet form, as DNA exists in cells. -
Triple Helix?
Linus Pauling and Robert Corey proposed a triple helix structure for DNA. -
The nobel prize in Physiology or medicine 1962
The Nobel Prize in Physiology or Medicine in 1962 was awarded to James Watson, Francis Crick and Maurice Wilkins for their discovery of the molecular structure of DNA, which helped solve one of the most important of all biological riddles. For the discoveries concerning the molecular structure of nucleic acids and its significance for information transfer in living material. -
DNA is a double-standed helix
The backbone is made of sugar (deoxyribose) and phosphate groups.
Hydrogen bonds between the nucleobases are: A-T and
G-C