Deoxyribonucleic acid (DNA), is the genetic material present in all living organisms (except in some prokaryotes). Its main function is to store genetic information, responsible for the construction and development of cells. A particular patch of DNA is called a gene, and many such genes form a structure called a chromosome. Genes contain the hereditary information of an individual and are responsible for the phenotypic (physical or external) characters and genotypic make-up. Genetic diseases are caused due to passing of certain abnormal genes, from the parents to the offspring. A specific set of chromosomes are present in a living organism, for example, human chromosomes are 23 in number.
Deoxyribonucleic acid consists of two strands of polynucleotides. In its structure, both strands are arranged in an anti-parallel manner, by which they run in opposite directions. The nucleotides are made up of base molecules, sugar molecules, and phosphate groups. The sugars and phosphates are joined by phosphodiester bonds, and in each of the sugar molecules, a base molecule is attached. DNA present in the nucleus of a cell is called nDNA; whereas, when it is located in the mitochondria of a cell, it's referred to as mitochondrial DNA or mtDNA.
While controlling cellular activity, DNA undergoes coding for synthesis of enzymes and proteins. In this step, its molecules are not converted directly to proteins, but are transcribed first as mRNA, which forms proteins. In genetics, the whole procedure of converting DNA to mRNA to proteins, is known as central dogma. The first step of converting DNA nucleotide to mRNA, is known as DNA transcription.
In this process, specific enzymes called RNA polymerases and other proteins play a major role. There are specific nucleotide sequences in the DNA strands, which act as start and stop points. During the initiation phase, these enzymes get attached to a specific 'promoter region' in one of the strands. With this signal, the double helix structure of DNA unwinds, allowing these enzymes to transcribe the DNA strand, to which it attaches.
The RNA polymerase synthesizes single-stranded mRNA polymer under the direction of a specific DNA strand, which acts as a template. This polymerase moves along it (3′ → 5′ direction) and continues to elongate the mRNA, until it reaches a specific 'terminator region' in the strand. As soon as the enzymes reach this particular nucleotide sequence, it detaches itself from the strand. At the same time, the mRNA polymer (or transcript ) is released into the nucleus, where the transcription takes place and gets completed.
These polymers undergo modification in the nucleus, after which they move to the cytoplasm for the translation process. In this part, the polymers, with the help of ribosomes and other enzymes, start synthesizing proteins. Thus, DNA transcription and translation work together for protein synthesis, which is very essential for gene expression. In fact, the characteristics are expressed by genes, via the proteins that they code for. With this understanding, researchers are still on the road to solve the mysteries of certain genetic diseases and disorders.