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Friedrich Miescher
While working in the Hoppe-Seyler's laboratory in Germany, Miescher was tasked with researching the composition of white blood cells. After discovering that large amounts of white blood cells were found in the pus from infections, he gathered bandages from a nearby clinic and washed off the pus. He experimented and isolated a new molecule nuclein. He determined that nuclein was composed of hydrogen, oxygen, nitrogen and phosphorus with there being a unique ratio of phosphorus to nitrogen. -
Frederick Griffith
In 1928, British bacteriologist Frederick Griffith conducted a series of experiments using pneumenia, bacteria and mice. Griffith was trying to develop a vaccine against pneumonia that was raging in Europe. In his experiments, Griffith used two related strains of bacteria, known as R(rough) and S(smooth). He found that the rough strain, when injected, would not cause sickness in mice, but the smooth strain with its polysaccharide coat would cause sickness because the bacteria would be protected. -
Oswald Avery, Maclyn McCarty, and Colin McCleod
Oswald Avery, Maclyn McCarty, and Colin McCleod set out to determine the chemical nature of the substance that allowed transformation. They confirmed that the substance was DNA, and that it is responsible for heredity, proving that Griffith's "transforming principle" was DNA. To do this they began with large cultures of heat-killed S cells and, through a long series of biochemical steps progressively purifying the transforming principle, ending with a highly purified transforming principle. -
Barbara McClintock
Barbara McClintock challenged existing concepts of what genes were capable of when she discovered that some genes could be mobile. Her studies of chromosome breakage in maize led her to discover a chromosome-breaking locus that could change its position within a chromosome. McClintock went on to discover mobile elements, now known as transposons. She also found that depending on where they inserted into a chromosome these mobile elements could reversibly alter the expression of other genes. -
Alfred Hershey and Martha Chase
The Hershey–Chase experiments were a series of experiments conducted by Alfred Hershey and Martha Chase that helped to confirm DNA is the genetic material. DNA had been known to biologists since 1869, but some scientists still assumed at the time that proteins carried the information for inheritance. Hershey and Chase used bacteriophages which are composed of DNA and protein and showed, infect bacteria, their DNA enters the host bacterial cell, but most of their protein does not. -
Erwin Chargaff
In the 1940’s Erwin Chargaff noticed that there was a pattern that occurred in the four bases (adenine, guanine, cytosine, and thymine). He took samples of different types of DNA from different cells and found that the amount of thymine was almost equal to the amount of adenine. He also found the amount of guanine was almost equal to the amount of cytosine. Both the purines were equal as well as both the pyrimidines were equal( A=T, C=G ) -
James Watson & Frances Crick
The 2 biochemists unlocked the mystery to life by determining the double helix structure of the DNA molecule. They played around with the shapes of the four bases, using paper models and combining them in different ways. Finally, they visualized a structure that solved the puzzle: If two of the bases were bonded in pairs (G with C), they took up the same space as the other pair (A with T). Hence, they could be arranged like steps on a spiral staircase. -
Linus Pauling
Linus Pauling was an American scientist who researched DNA and believed it was a three-chain helix with the bases facing outward and the phosphates in the core. He spent much time and pioneered in using technologies like X-ray diffraction for the studying of crystal structures. Pauling’s discoveries contributed to Watson and Crick’s breakthrough of the DNA double helix shape which helped scientists to Pauling’s discoveries contributed to Watson and Crick’s breakthrough of the DNA double helix. -
Mathew Meselsin & Franklin Stahl
The two discovered when the double stranded DNA helix is replicated, each of the two new double-stranded DNA helices consisted of one strand from the original helix and one newly synthesized. They decided the best way to tag the parent DNA would be to change one of the atoms in the parent DNA molecule. They decided to use an isotope of nitrogen to distinguish between parent and newly copied DNA. The isotope of nitrogen had an extra neutron in the nucleus, which made it heavier. -
Frederick Sanger
Sanger earned his Ph.D. by studying the metabolism of the amino acid lysine, and then he moved on to the study of insulin. Using chemistry and chromatography, and by mixing standard techniques with novel ones, he developed a method to read the amino acid sequence of insulin and found that this protein is actually made up of two amino acid chains linked together by disulphide bonds. -
Paul Berg
Paul Berg assembled the first DNA molecules that combined genes from different organisms. Results of his experiments, published in 1972, represented crucial steps in the subsequent development of recombinant genetic engineering. By stepwise methods such as he devised, individual genes could be isolated and inserted into mammalian cells or into such rapidly growing organisms as bacteria. The genes themselves could then be studied, and their protein products expressed. -
Kary Mullis
Mullis came up with the idea of using polymerase isolated from the extremophilic bacterium Thermophilus aquaticus. The polymerase, known as Taq polymerase, has optimal activity at 72°C and can withstand the 94°C required for denaturation of the DNA. This means that many reaction cycles could be performed without replenishing the enzyme.This breakthrough, together with advances in oligonucleotide synthesis made PCR both cost effective and convenient and it quickly entered mainstream research. -
J. Craig Venter
Venter was the primary force behind the human genome project. He also independently mapped out and sequenced human DNA. The importance of the genome sequencing effort is far-reaching and may result in the discovery of keys to the diagnosis and treatment of numerous diseases, from diabetes to heart disease to Alzheimer's disease.
