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History And Discovery Of Dna Essay

1059 words - 4 pages

DNA is the common name for Deoxyribonucleic acid. This is made up of nucleic acids containing deoxyribose (sugar), consisting of complex molecules, present in the chromosomes of all plant and animal cells, and carrying in coded form instructions for passing on hereditary characteristics.The DNA molecule takes the shape of a double helix, a simple structure that resembles gently twisted ladders. The rails of the ladder are made of pairs of nitrogen-containing nucleotides, which are subdivisions of DNA. Because each nucleotide within a rung of the DNA ladder is always paired with the same complimentary nucleotide, one half of the molecule can serve as a template for the construction of the other half. The four nucleotides in DNA contain the bases adenine (A), guanine (G), cytosine (C) and thymine (T).The people responsible for the discovery of the double-helical structure of DNA were Francis Crick, Rosalind Franklin, Linus Pauling, James Watson and Maurice Wilkins.To solve the structure of DNA four ideas had to come together:•The first was that the phosphate backbone was on the outside, bases on the inside.•That the molecule was a double helix.•That the strands were antiparallel.•That it had a specific base pairing.Erwin ChargaffTo understand the DNA molecule better, scientists were trying to make a model to understand how it works and what it does. In the 1940’s Erwin Chargaff noticed a pattern in the amounts of the four bases: adenine, guanine, cytosine, and thymine. He took samples of DNA of different cells and found that the amount of adenine was almost equal to the amount of thymine, and that the amount of guanine was almost equal to the amount of cytosine. Thus you could say: A=T, and G=C. This discovery later became Chargaff’s Rule.Rosalind Franklin and Maurice WilkinsRosalind Franklin and Maurice Wilkins decided to try to make a crystal of the DNA molecule. If they could get DNA to crystallize, then they could make an x-ray pattern, thus resulting in understanding how DNA works. These two scientists were successful and obtained an x-ray pattern. The pattern appeared to contain rungs, like those on a ladder between two strands that are side by side. It also showed by an “X” shape that DNA had a helix shape.Franklin found out that by bundling super thin strands of DNA and zapping them with a super fine x-ray beam there were two forms of hydration — the A form (easy to photograph) and the B form (hard to photograph). Her B form photographs showed a fuzzy cross, which meant a helix. Since the water would be attracted to the phosphates in the backbone, and the DNA was easily hydrated and dehydrated, she guessed that the backbone was on the outside and the bases were on the inside. The first part of the problem was solved. In May 1952 Franklin got the first good photograph of the B form of DNA. The photograph showed a double helix, which was the second part of the problem that had to be proved. In...

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