Central Dogma

Francis Crick was the first to postulate Central dogma of molecular biology in the year 1958.  He published this in Nature paper after restating in the year 1970. How the sequence information is passed on step by step, that is residue to residue transfer of information is defined by central dogma of life. No information can be passed on from one synthesized protein to other protein or any nucleic acid except retroviruses.

Dogma:

Dogma is a Series of framework or layout to understand the transfer of informations in sequence. In living organisms the sequential information transfer occurs in biopolymers.

Class of biopolymers:

Biopolymers are polymers that are synthesized by living microorganisms. For instance cellulose, chitin, starch are biopolymers which are made of sugar, nucleotides and amino acids. There are three important classes of biopolymers playing active role that are as follows.

• DNA which is stable unlike RNA, inert, tightly packed and long term storage is feasible
• RNA which is unstable and secondary structure is not sufficient. Some RNA has enzymatic activity.
• Proteins are programmed cells which completes analogy. Analogy is nothing but process of gene expression. Any obstruction in protein physical appearance can be result in genomic disability.

There are nine possible direct transfers of informations between three biopolymers. In which there can be three general transfer expected to occur in almost of the cells, three special transfers that can occur under specified conditions either in lab or in some viruses and three unknown transfer which will never happen. Only general transfer can transfer the information in proper way.

General transfer of sequential biological information:

General transfer of biological information is DNA duplication that is DNA copied to DNA. To transfer complete informations from parents to offspring DNA has to replicate itself. DNA replication takes place with the support of group of proteins which unwinds the DNA structure using enzyme called DNA polymerase and its proteins. Then informations of DNA are copied to mRNA (messenger RNA) also referred as transcription. Transcription takes place with the help of enzyme called RNA polymerase and other transcription factors. In case of eukaryotic cell pre mRNA, a primary transcript then processes through alternate splicing. In alternative splicing mRNA gets rearranged and produce different sequence. Translation occurs henceforth that is proteins are synthesized with the help of template that are present in mRNA. A prokaryotic cell has no nuclear compartments therefore transcription and translations are linked together. In case of eukaryotic cells, there is a special compartment for nucleus. Here mRNA transports information outside the nucleus wall to the place of translation that is cytoplasm. mRNA is encoded by triplet codons. DNA can never be converted to protein directly. RNA acts as a intermediate component to convert DNA into protein.

Special transfer of sequential biological information

Reverse transcription:

RNA can never be transfer the information back to DNA except retrovirus. It is just reverse of normally occurring transcription. Normal transcription synthesis RNA from DNA and hence it is referred as reverse transcription. Enzyme called Reverse transcriptase or DNA polymerase can assist this reverse transcription. RNA dependent DNA polymerase can form double stranded DNA from single stranded RNA after reverse transcribing in to single stranded cDNA (Complementary DNA).

RNA replication:

Transfer of information from single stranded RNA to the other is referred to as RNA replication. RNA dependent RNA polymerase helps in copying information from RNA to other. Many viruses replicates in this manner. Many eukaryotes replicate via RNA silencing method. RNA silencing is to express the genes by the generation of antisense RNA.

Direct translation:

Direct translation is the process of converting DNA directly into proteins. Direct translation is possible only when ribosomes are present without any contact cells. It is prevalent in cell free system. Using foreign DNA templates proteins can be expressed easily.

Methylation:

The change in addition of methyl group to DNA can result in gene expression. The process of gene expression takes place with the help of enzyme called DNA methylase. The addition can be epigenetic or somatic type. When the gene expression changes are hereditary then it is epigenetic. For instance cellular differentiation is epigenetic type. When changes are not hereditary it is somatic type. Here gene expresses without altering amino acid sequence of a protein.