The Central Dogma of Molecular Biology is a theory which tells us the direction of genetic information flow in cells. It was proposed by Francis Crick in 1958.
DNA is the carrier of instructions (called genetic code) which are used for production of proteins useful to an organism. DNA can be replicated and distributed to daughter cells, and hence the genetic code is preserved across generations. The information flow takes place from DNA to a messenger RNA (mRNA) molecule, which is then used to produce the required protein molecule. This entire process is divided into two steps, transcription and translation.
Transcription is transfer of information on DNA onto a messenger molecule called mRNA. This is followed by translation, where the RNA delivers this information to the ribosome (part of the cell responsible for protein production). Since the mRNA plies between DNA and the ribosome, it is called a ‘messenger’. The ribosome produces the protein as per the received instructions.
While most organisms follow the central dogma, there are exceptions. Baltimore and Temin theorised a process called reverse transcription, in which RNA is used as a template to produce DNA (the opposite of what happens in central dogma). An example of this are retroviruses, which use reverse transcription to transfer their genetic information from RNA to DNA. This DNA infects the cells of the viral host, causing the cell to produce the genetic material (and proteins) of the virus.
The role of the central dogma is to define the direction in which genetic information flows. It emphasises that genetic information flows from the nucleic acids to proteins and not vice versa.
Crick F, On Protein Synthesis, Symposia for the Society of Experimental Biology, (1958) Crick F, Central Dogma of Molecular Biology, Nature (1970) Varmus H, Reverse Transcription, Scientific American (1987)