Chapter X: The Genetic Code
Clearly the most important code not created by people is the genetic code. In 1953 it was realized by Watson and Crick that the order of the bases (chemical groups) in a DNA molecule formed a code that could be copied and passed from one generation to the next.
The four bases are Adenine(A), Thiamine(T), Guanine(G) and Cytosine(C). Sequences such as ACCGTCAT... form a code that was deciphered by Nirenberg, Matthaei and others in the early sixties. Part of the code contains the sequence of amino acids that the cell uses to make proteins. For example GGG specifies glycine and UCA specifies Serine. The code is redundant meaning that several different triplets code for the same amino acid. Often the third base doesn't matter. In RNA the base Uracil replaces Thiamine(T) as in the chart below.
The four bases are Adenine(A), Thiamine(T), Guanine(G) and Cytosine(C). Sequences such as ACCGTCAT... form a code that was deciphered by Nirenberg, Matthaei and others in the early sixties. Part of the code contains the sequence of amino acids that the cell uses to make proteins. For example GGG specifies glycine and UCA specifies Serine. The code is redundant meaning that several different triplets code for the same amino acid. Often the third base doesn't matter. In RNA the base Uracil replaces Thiamine(T) as in the chart below.
Later it was realized there were long sections of "junk" DNA that clearly didn't code for proteins. More recently it has been found that much of this code forms a complex system of switches to turn protein synthesis on and off.