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 ComponentsPhoebus Levene determined the components of DNA:
adenine, guanine, thymine, cytosine, deoxyribose phosphate. Defined phosphate-sugar-base units called nucleotide
Levene's TetranucleotideLevene proposed that there were four nucleotides per molecule.
Said DNA could not store the genetic code because it was chemically far too simple.
Griffith's Transformation ExperimentFrederick 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 McCartyDetermined 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: Protease (destroys protein), DNAse (destroys DNA)
Published the 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!
Counting NucleobasesErwin Chargaff 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 all the spices!
Hershey-Chase ExperimentsUsed 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
DNA, Double Helix and Picture 51The 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
DNADNA 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 gene
Triple Helix?Linus Pauling and Robert Corey proposed a triple helix structure for DNA
Pauling and Corey state that the core of the triple helix could contain either the bases, the sugars, or the phosphate groups. They argue that the core should be packed with a part of the nucleotide that can pack closely enough so bonds can be formed without being too crowded.