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Saturday, November 12, 2011

DNA Transcription

DNA Transcription

Deoxyribonucleic acid, in short DNA, is the genetic material of all living organisms (except in some prokaryotes). The main function of DNA is to store genetic information, responsible for the construction and development of all cells. A stretch of DNA is called a gene and many genes makeup a structure called 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 46 in number.

DNA is a nucleic acid, consisting of two strands of polynucleotides. In a DNA structure, the two nucleotide strands are arranged in an anti-parallel manner, in 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 or simply DNA; whereas, DNA located in the mitochondria of a cell is referred to as mitochondrial DNA or mtDNA. Let's take a look at eukaryotic DNA transcription for expression of genes.

DNA Transcription: A Brief Explanation

While controlling cellular activity, DNA undergoes coding for synthesis of enzymes and proteins. In the process of protein synthesis, the DNA molecules are not converted directly to proteins, but they are transcribed first as mRNA (messenger RNA), which is then translated to proteins. In genetics, the whole process of converting DNA to mRNA to protein is known as central dogma. The first step of transcribing DNA nucleotide to mRNA is known as DNA transcription. Let's discuss in brief about the transcription of nDNA.

In DNA transcription, specific enzymes called RNA polymerases and other proteins play a major role. There are specific nucleotide sequences in the DNA strand, which act as start and stop point. In the initiation phase, RNA polymerase enzyme attaches to a specific 'promoter region' in one of the DNA strand. With this signal, the double helix structure of DNA unwinds, allowing the RNA polymerase to transcribe the DNA strand to which it attaches.

During the transcription process, the RNA polymerase synthesizes single-stranded mRNA polymer under the direction of the specific DNA strand, which acts as template. The RNA polymerase moves along the DNA strand (in 3′ → 5′ direction) and continues to elongate mRNA polymer, until it reaches a specific 'terminator region' in the DNA strand. As soon as the RNA polymerase reaches this particular nucleotide sequence, it detaches itself from the DNA strand. At the same time, the mRNA polymer (or transcript ) is released into the nucleus where the DNA transcription takes place. Thus, DNA transcription is completed.

The mRNA polymer that results from DNA transcription undergoes modification in the nucleus, after which they move to the cytoplasm for translation process. In the cytoplasm, the mRNA polymers with the help of ribosomes and other enzymes synthesize proteins. This way, 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, DNA researches are ongoing to solve the mystery of certain genetic diseases and disorders.

1 comment:

  1. I appreciate all of the information that you have shared. Thank you for the hard work!
    Klenow (3′→ 5′ exo-) is a mesophilic dna polymerase deficient in both proofreading (3′→ 5′) and nick-translation (5′→ 3′) nuclease activities, and that displays a moderate strand displacement activity during DNA synthesis.