-
Discovery of Nucleic Acids
Swiss chemist Friedrich Miescher first isolates a substance that he calls "nuclein" from the nuclei of white blood cells. -
Discovery of DNA Components
In 1909, Phoebus Levene discovered all of the components of DNA, and actually defined the unit, including the sugar, the phosphate, and the base which he called a nucleotide. -
Levene's Tetranucleotide
Levene proposed that there were four nucleotides per molecule, he said DNA could not store the genetic code because it was chemically far too simple. Unfortunately, this theory about the structure of DNA was incorrect. -
Griffith Experiments
The Griffith experiments, conducted by British bacteriologist Frederick Griffith in 1928, showed that genetic information could be transferred between bacteria, demonstrating the process of transformation. This discovery laid the foundation for the field of bacterial genetics and paved the way for future breakthroughs in molecular biology. -
Avery, McLeod and McCarty
Oswald Avery, Colin MacLeod, and Maclyn McCarty were three scientists who performed a series of experiments in the 1940s that helped to confirm that DNA is the genetic material. They conducted a series of experiments using a strain of Streptococcus pneumoniae and purified different components of the bacterium, including DNA, RNA, and protein, to determine which component was responsible for the transfer of genetic information. -
Avery, McLeod and McCarty
Oswald Avery, Colin MacLeod, and Maclyn McCarty were three scientists who performed a series of experiments in the 1940s that helped to confirm that DNA is the genetic material.They conducted a series of experiments using a strain of Streptococcus pneumoniae and purified different components of the bacterium, including DNA, RNA, and protein, to determine which component was responsible for the transfer of genetic information. -
Avery, MacLeod and McCarty (Experiment Explanation)
Avery, McLeod, and McCarty worked with two types of Streptococcus pneumoniae bacteria, virulent and non-virulent, and extracted different molecules from them. When they injected the extracted DNA from the virulent bacteria into non-virulent bacteria, the non-virulent bacteria transformed into the virulent form. This demonstrated that DNA is the molecule responsible for the transmission of genetic information, as other extracted molecules, did not have this transformative effect. -
Chargaff's rules
Erwin Chargaff established his rules in the late 1940s. Specifically, his findings were published in a series of scientific papers in the 1950s.This rules state that the amount of adenine in DNA is equal to the amount of thymine, and the amount of guanine is equal to the amount of cytosine. -
Pauling's Triple Helix
Linus Pauling proposed a "triple helix" model of DNA in 1951, which suggested that the molecule was composed of three intertwined chains. This model was later proved incorrect with the discovery of the double helix structure of DNA. -
Watson and Crick Inside-Out Double Helix
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 -
Rosalind Franklin Photo 51
Photo 51 taken by Rosalind Franklin in 1952 is a crucial X-ray diffraction image of DNA crystals. It provided valuable information on the 3D structure of DNA, but was shared with James Watson and Francis Crick without Franklin's consent. The information from Photo 51 was used by Watson and Crick in determining the double helix structure of DNA -
Hershey-Chase Experiments
The Hershey-Chase experiments, conducted by Alfred Hershey and Martha Chase in 1952, provided evidence that DNA, and not protein, is the genetic material of viruses. Using radioactive isotopes, Hershey and Chase were able to trace the movement of genetic material within a bacteriophage and demonstrate that the genetic material was located in the virus's DNA. These experiments helped to confirm the discovery of DNA's role as the genetic material. -
Watson and Crick Correct Double Helix
In 1953, Watson and Crick discovered the structure of DNA, which they described as a double helix. This discovery revolutionized the field of genetics and paved the way for our understanding of heredity and the mechanisms of evolution. The double helix model, with its complementary base pairing, explained how genetic information could be accurately passed from one generation to the next.