CENTRAL DOGMA: AN OVERVIEW

central Dogma is the relationship between DNA, RNA and proteins.

It was proposed by CRICK in 1958.

Crick proposed that the information present in DNA is transferred to DNA via replication and to RNA via transciprtion. Transciprtion leads to the production of tRNA, mRNA, rRNA. Now, mRNA undergoes translation to form proteins. 

This relationship between RNA, DNA and protein is known as central dogma in which information flows from DNA → RNA→ PROTEIN and never in reverse.

Following is a basic idea of all these three processes.

DNA Replication is the process of making 2 identical copies of DNA from one original DNA copy. 

Essentially the DNA “unzips” and each of the original strands acts as a template for the new strands. 

DNA is synthesized in a 5’–>3’ direction during the S phase of the cell cycle.

Transcription is when template DNA strand is converted to complementary RNA. 

The RNA is very similar to DNA, except that it has Uracil (U) in place of Thymine (T) and it is single stranded.

RNA is synthesized in a 5′ –> 3′ direction as the RNA Polymerase moves along the DNA in a 3′–> 5′ Direction.

Post-Transcriptional Modification (RNA Processing) is the process of converting immature RNA to mature RNA that is ready to be translated.  5'- capping, 3'- tailing, splicing are carried out.

Translation is the process by which a RNA sequence is converted into a set of amino acids (AKA a protein) using tRNA, ribosomes and translation factors.

NOTE:The central dogma of biology holds that genetic information normally flows from DNA to RNA to protein. As a consequence it has been generally assumed that genes code for proteins, and that proteins fulfill most structural and catalytic and also most of the regulatory functions, in all cells, from microbes to mammals. 

However, the latter may not be the case in complex organisms.

This is because the concept of central dogma is just a simple interpretation of the exchange of genetic information going inside the cell; and, a simple interpretation often ignores many complications just to make things simple or easy to understand. 
central dogma was proposed in 1950s and many other parts and processes related to DNA, RNA and proteins known then and the one which are continuously discovered today are not included.

e.g. The presence of non-coding RNA (ncRNA), Alternative splicing, reverse transcriptase, introns, junk DNA, epigenetics, RNA viruses, trans-splicing, transposons, prions, epigenetics, and gene rearrangements are ignored to simplify things.

Exceptions also exist in the form of RETROVIRUSES. They carry out reverse transciption and RNA dependent RNA replication.
e.g. in TMV (tobacco mosaic virus),ΦR17, ΦMS2 etc. the viral RNA is able to replicate itself and carry out RNA to RNA change with the help of RNA replicase.
similarly, RSV (ross sarcoma virus) can change RNA to DNA using reverse transcriptase. This process is called reverse transcription.

Reverse transcription and RNA dependent RNA replication and other above mentioned parts and processes doesn't form a part of central dogma.

Only DNA replication, transcription, and translation forms a part of it.

A number of startling observations and phenomena suggests that the traditional view of genetic regulatory systems in animals and plants may be incorrect.

It will take years, perhaps decades, to construct a detailed theory that explains how DNA, RNA and the epigenetic machinery all fit into an interlocking, self- regulating system.

But there is no longer any doubt that a new theory is needed to replace the central dogma that has been the foundation of molecular genetics and biotechnology since the 1950s.

The central dogma, as usually stated, is quite simple: DNA makes RNA, RNA makes protein, and proteins do almost all of the work of biology.