CENTRAL DOGMA (FRAMEWORK) OF MOLECULAR BIOLOGY

The central framework of molecular biology otherwise known as the “central dogma” is the starting point for the actual course of movement of genetic information within the cell’s nucleus of an organism. The transfer of genetic information within the cell of an organism (i.e. in the nucleus) from deoxyribonucleic acid (DNA) to ribonucleic acid (RNA) and then to proteins is generally known as the central dogma of molecular biology. DNA, RNA and proteins are generally known as macromolecules; and in contrast to other macromolecules, these informational macromolecules contain genetic information or gene sequences that control the day to day activities of the cell and the whole organism. The transmission of these informational macromolecules of life commonly follows this path of central dogma.

Central dogma is the main center-piece of molecular biology and genetics in particular. After the cellular machinery of the ribosome translates the RNA molecule transcripts from the DNA molecule to form specific amino acid chains that makeup protein molecules through the processes of translation and transcription respectively, the protein molecules so synthesized has unique biochemical and physiological functions within the cell and each of these proteins is further expressed in the cell as observable physical traits or phenotypes in the whole organism. The phenotypes showcases the actual genetic information encoded by the DNA or genes of the organism; and it is these traits that help molecular biologists to decipher defects or mutation that occur in the whole organism after a particular gene or DNA molecule have been completely expressed.

Despite the fact that the DNA is the actual genetic blueprint of the cell, it is the protein molecules that actually carry out all of the metabolic processes that go on in the cell of an organism. Therefore, the DNA provides the genetic information or instruction for work while the proteins of the cell do the work. Proteins are informational macromolecules that comprises of long chains of amino acids; and they are the most important components of the physiological and biochemical metabolic pathways of the cell of an organism. They are mainly responsible for growth and the repair of worn out tissues.       

Central dogma describes the genetic process in which the information encoded by a gene or DNA is transcribed into messenger ribonucleic acid (mRNA) that act as a template and is further translated into specific protein molecules in the ribosome of a cell. It is mainly comprised of two main processes which are transcription and translation; and these shall be highlighted in this section. The illustration of the central dogma is shown in Figure 1 and it is a descriptive analysis of the genetic code of belief especially as it pertains to the pattern in which hereditary or genetic materials are inherited and/or passed from parent progenitor cells to their offspring. It shows how the 3 most important informational macromolecules (DNA, RNA & protein) of a cell or the whole organism are synthesized.

The DNA of eukaryotic cells is often wrapped in specialized protein molecules known as histones, and this orientation forms the chromosome of the cell. However, in prokaryotic cells, the DNA is wrapped with non-histone proteins to form the cells chromosome. DNA is the main genetic material of the cell, and genetic information flows from it to the RNA which is expressed in the cell (as directed by the genetic sequence encoded by the DNA) to form proteins. Central dogma shows how genetic information flows from one macromolecule to another in a controlled manner within the cell of living organisms.

The three important processes of this flow of genetic information are as follows:

• Transcription

• Translation

• DNA replication

• Transcription is the synthesis of an RNA molecule (mRNA in particular) that is complementary to one of the 2 single strands (ss) of a double-stranded DNA molecule (dsDNA). It is catalyzed by RNA polymerase. The genetic information or gene sequence required to synthesize the ribonucleic acid (RNA) molecule is encoded by the DNA molecule. Thus for the RNA molecule to be synthesized, genetic information has to be transferred in a controlled fashion to the messenger RNA (mRNA) through the process of transcription.  

• Translation is the synthesis of protein molecules using the genetic information in the messenger RNA (mRNA) as a template. Amino acids are the building blocks or main units of protein molecules, and they are arranged in the form of a polypeptide. The mRNA encodes one or more polypeptides, and this is dependent on the specific sequence of bases in the mRNA. It is noteworthy that each group of 3 bases on an mRNA actually codes for a single amino acid (e.g. tryptophan). Such triplets of bases are known as codons. Codons are sequences of 3 bases in an mRNA that encodes specific amino acids.

References

Alberts B, Bray D, Lewis J, Raff M, Roberts K and Watson J.D (2002). The molecular Biology of the Cell. Fourth edition. New York, Garland, USA.

Chen I and Dubnau D (2004). DNA uptake during bacterial transformation. Nat. Rev. Microbiol. 2 (3): 241–249.

Cooper G.M and Hausman R.E (2004). The cell: A Molecular Approach. Third edition. ASM Press.

Dale J (2003). Molecular genetics of bacteria. Jeremy W. Dale and Simon Park (4^th eds.). John Wiley & Sons Ltd, West Sussex, UK. Pp. 312-313.

Das H.K (2010). Textbook of Biotechnology. Fourth edition. Wiley edition. Wiley India Pvt, Ltd, New Delhi, India.

Lewis R (2004). Human Genetics: Concepts and Applications. Sixth edition. McGraw Hill Publishers, USA.

Lodish H, Berk A, Matsudaira P, Kaiser C.A, Kreiger M, Scott M.P, Zipursky S.L and Darnell J (2004). Molecular Cell Biology. Fifth edition. Scientific American Books, Freeman, New York, USA.

Madigan M.T., Martinko J.M., Dunlap P.V and Clark D.P (2009). Brock Biology of Microorganisms, 12^th edition. Pearson Benjamin Cummings Inc, USA.

McPherson M and Moller S (2002). PCR: The Basics. 2^nd edition. Taylor and Francis Group. New York, USA.

Sambrook, J., Russell, D.W. (2001). Molecular Cloning: a Laboratory Manual, 3rd edn. Cold Spring Harbor Laboratory Press, New York.

Synder L, Peters J.E, Henkin T.M and Champness W (2013). Molecular Genetics of Bacteria. Fourth edition. American Society of Microbiology Press, USA.

Tamarin Robert H (2002). Principles of Genetics. Seventh edition. Tata McGraw-Hill Publishing Co Ltd, Delhi.