ADVERTISEMENTS:
After reading this article you will learn about the central dogma of molecular biology, with help of a suitable diagram.
Crick’s Central Dogma:
DNA, deoxyribonucleic acid, carries the information necessary for an organism to grow and develop. This information is housed deep within the nucleus of a cell in genes – highly- specific sequences of nucleotides, the building blocks of DNA. Information flow (with the exception of reverse transcription) is from DNA to RNA via the process of transcription, and then to protein via translation (Fig 8.1). Transcription is the making of an RNA molecule of a DNA template. Translation is the construction of an amino acid sequence (polypeptide) from an RNA molecule. Although originally called dogma, this idea has been tested repeatedly with almost no exceptions to the rule being found.
Proteins are one of the most important structural and functional units of cell. They are organic compounds made up of amino acids arranged in a linear chain. The amino acids are joined together by the peptide bonds between the carboxyl and amino groups of adjacent amino acid residues. Proteins are the information impregnated in the DNA, the blue print of life. They are synthesized through the intermediate mRNA, transcribed product of DNA. The sequence of amino acids in a protein is defined by the sequence of a gene, which is encoded in the genetic code.
In general, the genetic code specifies 20 standard amino acids, however in certain organisms the genetic code can include selenocysteine and in certain archaea pyrrolysine. All the biochemical pathways are controlled by the enzymes, basically composed of proteins. Virtually all the phenotypes examined so far are the result of biochemical reactions that occur in the cell. Since any error in the protein synthesis may leads to disease conditions, it should be of high fidelity.
A strand of RNA appears to be similar to a strand of DNA, which is called the coding strand. It is complementary to the other strand that provides and serves as template strand for its synthesis, only except for uracil that substitutes thymine, in the 2′ position of hydroxyl group. These small differences however confer on RNA the potential for much greater structural diversity compared to DNA, a diversity that allows RNA to assume a variety of cellular functions.
Translation is the RNA directed synthesis of polypeptides. This process requires all three classes of RNA. Although the chemistry of peptide bond formation is relatively simple; the processes leading to the ability to form a peptide bond are exceedingly complex. The template for correct addition of individual amino acids is the mRNA, yet both tRNAs and rRNAs are involved in the process.
ADVERTISEMENTS:
The tRNAs carry activated amino acids into the ribosome which is composed of rRNA and ribosomal proteins. The ribosome is associated with the mRNA ensuring correct access of activated tRNAs and containing the necessary enzymatic activities to catalyze peptide bond formation. Biochemical reactions are controlled by enzymes, and often are organized into chains of reactions known as metabolic pathways. Loss of activity in a single enzyme can inactivate an entire pathway.
