Genetic Code

A code is used for converting one type of symbolism to another. For example, the ASCII code of computers specifies that each letter of the keyboard has a numerical equivalent - "A" is equivalent to ASCII code 65, etc.

Cells encode information about the sequence of amino acids for making proteins in nucleic acids. This is called the genetic code.

Nucleic acids are polymers of four different nucleotides, whereas proteins are polymers of 20 different amino acids. Thus, each nucleotide cannot stand for one amino acid. Neither can two nucleotides code for one amino acid, because there would be only 16 combinations of two nucleotides (42 = 16). In reality, three nucleotides code for one amino acid in a protein (43 = 64, so there is room for redundancy in the genetic code). The grouping of three nucleotides that code for one amino acid is called a codon.

The genetic code is used in the process of translation to make proteins. We refer to any region of DNA that codes for protein as a "coding sequence" or a "coding region."

The genetic code is fairly "universal," meaning that the same code is used by all organisms, from bacteria to humans. A few rare variations of the genetic code are known, but they are the exception, not the rule.

See also: Nucleotides, Codons, Genetic Code (from Chapter 27), Stop codon, mRNA, 1&3 Letter Amino Acid Codes

INTERNET LINK: Reading the Message in Genes