The chromosomal DNA contains complete information about all the specific proteins to be synthesized in the cell for their needs. It is coded in the DNA as the particular sequence of bases called genetic code. The unit of genetic information is called codon which is a group of three adjacent deoxyribonucleotides that specify a single amino acid in a polypeptide chain. A polypeptide is a single chain of amino acid. Theinformation for the synthesis of polypeptide chains of proteins is found on DNA molecule. This information is given to single stranded RNA molecules which act as a messenger. The messenger RNA transfers the message to ribosomes for the synthesis of a protein molecule. This unidirectional flow of information from DNA to RNA and from RNA to protein is called central dogma.
Central dogma of molecular biology was proposed by Crick in 1958.In this genetic information is stored inthe 4 letter language of DNA.The same is transferred during transcription to 4 letter language of messenger RNA but with two differences.
1. Complementation in code language
2. Replacement of letter T with U.
In 1970 Temin and Baltimore discovered retroviruses which contain RNA as genetic material. The virus produce an enzyme called reverse transcriptase which performs the central dogma reverse by synthesizing DNA over template of genetic RNA.The newly synthesized DNA then functions as a master copy producing RNAs controlling translation to synthesize polypeptides. The process of formation of DNA from RNA is called reverse transcription.