Central dogma of molecular biology
The central dogma of molecular biology (sometimes Crick's central dogma after Francis Crick who coined the term and discovered some of the principles) states that the flow of genetic information is "DNA to RNA to protein". With a few notable exceptions, all biological cells conform to this rule.
It can be stated in a very short and oversimplified manner as "DNA makes RNA makes proteins, which in turn facilitate the previous two steps as well as the replication of DNA", or simply "DNA->DNA->RNA->protein". This process is therefore broken down into three steps: transcription, translation, and replication. By new knowledge of the RNA processing, a fourth step must be included: splicing.
Transcription
Transcription is the process by which the information contained in a section of DNA is transferred to a newly assembled piece of messenger RNA (mRNA). It is facilitated by RNA polymerase and transcription factors.
Splicing
In eukaryote cells the primary transcript (pre-mRNA) is processed. One or more sequences (introns) are cut out. The mechanism of alternative splicing makes it possible to produce different ripe mRNA molecules, depending on what sequences are treated as introns and what remain as exons.
Translation
Eventually, this ripe mRNA finds its way to a ribosome, where it is translated. The ribosome's function is to take individual amino acids of the correct kind and link them in a chain in the right order, based on the sequence of the mRNA. Once the amino acids are linked into the chain, they are released from the ribosome and fold into a new protein. Sometimes this folding process has to be helped along by other proteins, called chaperone proteins. Occasionally proteins themselves can be further spliced, when this happens the inside "discarded" section is known as an intein.
Replication
Finally, back to where we started, a protein called DNA polymerase opens up the DNA and with the help of several other proteins allows the DNA to replicate itself.
Exceptions to the central dogma
The central dogma is not really a dogma in the traditional sense of the word, like all scientific theories it is modified as we learn more details of the processes.
The biggest revolution in the central dogma was the discovery of retroviruses, which transcribe RNA into DNA through the use of a special enzyme called reverse transcriptase has resulted in an exception to the central dogma; RNA->DNA->RNA->protein. Also, some virus species are so primitive that they use only RNA->proteins, having not developed DNA. With the discovery of prions, a new exception to the central dogma has been discovered, Protein->Protein. That is, proteins directly replicating themselves by making conformational changes in other proteins. Although retroviruses, certain primitive viruses, and prions may violate the central dogma, they are technically not considered "alive", and thus the rule that "all cellular life follows the central dogma" still holds true.
See also
