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Discovery of Nucleic Acids
Friedrich Miescher isolated the genetic material from white blood cell nuclei. He noted it had an acidic nature and called it NUCLEIN -
Levene's Tetranucleotide
Levene proposed that there were four nucleotides per molecule.
Said DNA could not store the genetic code because it was chemically far too simple. -
Discovery of DNA Components
Phoebus Levene who lived between 1869 and 1940 determined the components of DNA:
- adenine
- guanine
- thymine
- cytosine
- deoxyribose phosphate
Defined phosphate-sugar-base units called nucleotides. -
Frederick Griffith and his Transformation Experiment
He 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
Oswald Avery, Colin MacLeod, and Maclyn McCarty were three scientists who made some experiments in the 1940s to confirm that the DNA was the real genetic material. They did a series of experiments with a strain of Streptococcus pneumoniae and purified different components of the “bacteria” (including also DNA, RNA, and protein) to determine which component was the responsible for transferring the genetic information. They discovered it was the DNA, not the protein. -
Pauling's and Corey's Triple Helix
Linus Pauling and Robert Corey proposed a triple helix structure for DNA. They first proposed the concept of the Triple Helix model in the 1951, however, they were probed wrong with the discovery of the double helix structure of DNA. -
Erwin Chargaff and his "Counting Nucleobases"
He used some paper chromatography and UV spectroscopy to examine the amount of the nucleobases and he started to notice something odd...
This came to be known as "Chargoff's Rules"
Amounts of Adenine = Amounts of Thymine
Amounts of Cytosine = Amounts of Guanine Always in every single alife spiece. -
Hershey-Chase Experiments
He used phages and radiolabeled phosphorus and sulfur.
It was thaought that the geneitc material was protein, but thanks to Hershey and Chase, it was discovered concluded that DNA, not protein, was the genetic material.
A protective protein coat was formed around the "bacteriophage", but the internal DNA is what has the ability to produce progeny inside bacteria. -
Watson and Crick, "double helix"
They 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
However, this model was quickly shown to be incorrect as it made no chemical sense. During the race to uncover the structure of DNA, Jim Watson and Francis Crick either stole Rosalind Franklin's data, or 'forgot' to credit her. -
Rosalind Franklin (the true founder of DOUBLE HELIX)
Rosalind Franklin was a British scientist who played a prominent role in the greatest milestone in the development of molecular biology, the discovery of the structure of DNA. She received her doctorate in physical chemistry in 1945 from Cambridge University. She studied X-ray diffraction techniques for three years at the Central Laboratory of Chemical Services of the State of Paris. Dispite her discovery, she was never rewarded for what she did for science as it was stolen by Watson and Crick -
Watson and Crick, the CORRECT model of "double helix"
Watson and Crick described DNA as a double helix. their discovery was considered revolutionary in genetics and created the path for our understanding in heredity and the mechanisms of evolution. The double helix model which has a complementary base pairing, proved how genetic information could be passed from one generation to the next. This is why, this discovery is considered one of the most important in the science history. -
What we know NOW
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