DNA structure
The structure of DNA
James Watson and Francis Crick worked out the structure of Deoxyribonucleic acid. The material inside the nucleus of cells, carrying the genetic information of a living being. in 1953. By using data from other scientists (Rosalind Franklin and Maurice Wilkins) they were able to build a model of DNA. The X-ray crystallography data they used showed that DNA consists of two strands coiled into a The shape of the DNA molecule, with two strands twisted together in a spiral..
Image caption, The famous X-ray diffraction photograph of DNA taken by Rosalind Franklin, known as photograph 51.
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DNA is a polymer made from four different The units or molecules of which DNA or RNA is composed. These are arranged in a repeating fashion. Each nucleotide consists of alternating sugar and phosphate sections with one of the four different bases attached to the sugar.
Base pairs
Each strand of Deoxyribonucleic acid. The material inside the nucleus of cells, carrying the genetic information of a living being. is made of chemicals called bases. Note that these are different to bases in relation to acids and alkalis in chemistry.
There are four different bases in DNA:
- thymine, T
- adenine, A
- guanine, G
- cytosine, C
There are chemical cross-links between the two strands in DNA, formed by pairs of bases. They always pair up in a particular way, called complementary base pairing:
- thymine pairs with adenine (T-A)
- guanine pairs with cytosine (G-C)
A sequence of three bases is the code for a particular amino acid, which is known as a triplet or the triplet code. The order of the bases controls the order in which amino acids are assembled to produce a particular protein.