Dr. Aithal's Genetics: Nov 23, 2008

THE DNA

In 1951, the then 23-year old biologist James Watson traveled from the United States to work with Francis Crick, an English physicist at the University of Cambridge. Crick was already using the process of X-ray crystallography to study the structure of protein molecules. Together, Watson and Crick used X-ray crystallography data, produced by Rosalind Franklin and Maurice Wilkins at King's College in London, to decipher DNA's structure. This is what they already knew from the work of many scientists, about the DNA molecule:
DNA is made up of subunits which scientists called nucleotides.
Each nucleotide is made up of a sugar, a phosphate and a base.
There are 4 different bases in a DNA molecule:
adenine (a purine)
cytosine (a pyrimidine)
guanine (a purine)
thymine (a pyrimidine)
By rule the number of purine bases equals the number of pyrimidine bases, which is known as Chargaff's Rule.
The number of A equals to T & G equals to C
The basic structure of the DNA molecule is helical and supercoiled, with the bases being stacked on top of each other. DNA can adopt a more compact configuration due to supercoiling. The degree of supercoiling in the cell is carefully controlled by the action of topoisomerases.