Timeline: 1966
Structure of DNA
Codon Table

Web Links:
The Genetic Code
Dogma, DNA, & Enzymes

DNA is made up of four nucleotide bases, adenine (A), thymine (T), cytosine (C), and guanine (G). These bases are arranged in DNA and RNA in triplets, called codons. Codons, which are specific sequences of three bases, code for specific amino acids, which are the building blocks of proteins. The way in which DNA produces RNA, which in turn produces a protein, is known as the central dogma.

RNA is produced directly from DNA, creating a complementary sequence of ribonucleic acid. This process is referred to as transcription. RNA differs from DNA in that thymine has been replaced by uracil. For example, the DNA sequence GATCATCG would be transcribed as CUAGUAGC in RNA. RNA is produced from DNA by an enzyme called RNA polymerase.

RNA is composed of three major types: messenger, transfer and ribosomal. Messenger RNA is the type used to transfer the genetic information from DNA to proteins. Messenger RNA is produced from the DNA template and contains the information for coding for various types of proteins. The synthesis of proteins from messenger RNA is called translation. Transfer RNA and ribosomal RNA function in this process in several ways. The various transfer RNAs carry specific amino acids to the ribosomal-mRNA complex (the site of protein synthesis). They recognize the specific codons by carrying in their structure a specific anticodon sequence which bonds to the codon site. This process must be started by the start codon, AUG. The amino acids then combine to form a polypeptide chain until a stop codon is reached. The transfer RNA anticodon for a stop codon contains no amino acid. The chain then breaks off and forms a protein.

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