More at 10 nanometers
The key to the ability of DNA to encode information for the production of proteins lies in the nitrogen-containing bases. There are only four different bases used in DNA: adenine (A), thymine (T), guanine (G), and cytosine (C). Adenine always bonds to thymine, and guanine always binds to cytosine. Thus, if one rung of the DNA ladder contained the sequence of bases 'AGCTGA', the complimentary rung would contain 'TCGACT'. It is worth emphasizing that all of Earth's life, from viruses to man, whether plant or animal, uses the same four bases in its DNA.
Proteins are the major component of most cell structures and control virtually all of the chemical reactions of living matter. The ability of proteins to assist in chemical reactions depends on its molecular shape, which is further dependant on its composition. Proteins are made up of components called polypeptides and polypeptides are chains of amino acids. Twenty different amino acids are commonly found in polypeptides. So, proteins are essentially strings of amino acids, their order determining the structure and function of the protein.
Genetic scientists reasoned that there must be a code by which the string of four bases in the DNA could determine a sequence of amino acids. It was determined that a sequence of exactly three bases was needed to define each of the 20 amino acids. Since there are 64 possible* triplets of bases (called 'codons') many amino acids are coded by more than one triplet, providing some redundancy within the code.
*There is one of four possible bases in each of the three positions of a triplet -- thus, 4 x 4 x 4 = 43 = 64.
Copyright © 2016 by Bruce Bryson