Race to DNA Race for DNA Race for

Race to DNA

Race for DNA • Race for DNA got on fire 1952 when DNA was identified as the material basis of heredity by HERSHEY and CHASE. • The race was on to determine the structure of DNA as it exists in cells, wet and at p. H = 7.

Discovery of the DNA structure • JAMES WATSON, a 23 year old American biochemist and FRANCIS CRICK, a 35 year old English physicist met 1951 together at the Cavendish labs at Cambridge University. • WATSON and CRICK were model builders. First DNA model WATSON and CRICK had build was in 1951 and published in a science magazine described DNA as a double helix with phosphates and sugars at the center and the bases facing the outside. Do you see the problem of this model? This model was incorrect because the negative charged phosphates coming together at the center would bring the molecule to explosion.

Race to discover the molecule of life • Everybody knew the discovery of ERWIN CHARGAFF 1952. He figured out that in each species the amount of purine base A is the same as pyrimidine base T and the amount of purine base G is the same as pyrimidine base C (CHARGAFF rules). A=T G=C • By building new models of the DNA WATSON and CRICK saw that a big purine base and a small pyrimidine base fits together by hydrogen bonds and that the size of both base pairs is the same.

Race to discover the molecule of life • In January 1953 the already famous scientist LINUS PAULING, who discovered the helix structure of proteins, published his DNA model, a triple helix with bases facing to the outside. Do you see the problem of his model? E. g. : - There is no explanation how the three strands could keep together - It couldn`t explain A = T and G = C One of the world’s leading scientists went wrong with his approach to determine the structure of this hugely-important molecule. In reality, he wanted to be the first to publish a roughly correct structure of DNA.

Last puzzle stone to the discovery • In January 1953 WATSON visited MAURICE WILKINS who was a famous crystallographer at King`s College in London 50 miles away from Cambridge. • WILKINS had the talented crystallographer ROSALIND FRANKLIN in his team.

Last puzzle stone to the discovery • During the visit WILKINS showed him the X-Ray pictures of ROSALIND she made in 1951 out of in vivo DNA. She was also in the race for the discovery but she couldn`t build a DNA model out of her results. • ROSALIND didn`t know that her boss Wilkins got her pictures and showed them to WATSON.

Last puzzle stone to the discovery

Discovery of the double helix When WATSON saw the X-Ray picture he immediately knew what it meant, he saw the evidence for the double helix of DNA. On April 25 th in 1953 WATSON and CRICK published their DNA model of a double helix in science magazine Nature: • A double helix structure with base pairs looking to the center and a backbone made of sugars and phosphates. • Base pairs with a purine base and a complementary pyrimidine base which fits together by hydrogen bonds keeping the two strands together. • Both strands are antiparallel, only in this orientation two complementary nucleotides can build a base pair inside the backbone of DNA.

Watson and Crick in front of her model

Awarded by the Nobel Prize • WATSON and CRICK and MAURICE WILKINS won the Nobel Prize for medicine and physiology at 10 th December 1962. • In 1962 ROSALIND has already passed away at the age of 37 by ovary cancer in 1958 induced by the X-rays. • Neither of the three Nobel Price winners acknowledged the importance of her work in their discovery.

Awarded by the Nobel Prize Wilkins Crick Watson

Let`s see the sumerizing video https: //www. youtube. com/watch? v=59 Xn. Rgnkc. B 8