Transcription how does it work

But what about transcription in particular? DNA, rather famously, is woven into a double-stranded helix. But in this form, it would physically be difficult to build anything from it. Therefore, in the initiation phase or step of transcription, the DNA molecule is unwound by enzymes called helicases. This strand is referred to as the noncoding strand, because, thanks to the rules of DNA and RNA base-pairing, the other DNA strand has the same sequence of nitrogenous bases as the mRNA to be synthesized, thus making this strand the coding strand.

Based on points made previously, you can conclude that a strand of DNA and the mRNA it is responsible for manufacturing are complementary. With the strand now ready for action, a section of DNA called the promoter sequence indicates where transcription is to start along the strand.

The enzyme RNA polymerase arrives at this location and becomes part of a promoter complex. All of this is to ensure that mRNA synthesis begins exactly where it is supposed to on the DNA molecule, and this generates an RNA strand that holds the desired coded message. Next, in the elongation phase, RNA polymerase "reads" the DNA strand, starting at the promoter sequence and moving along the DNA strand, like a teacher walking up a row of students and distributing tests, adding nucleotides to the growing end of the newly forming RNA molecule.

The bonds created between the phosphate groups of one nucleotide and the ribose or deoxyribose group on the next nucleotide are called phosphodiester linkages. Note that a DNA molecule has what is called a 3' "three-prime" terminus at one end and a 5' "five-prime" terminus at the other, with these numbers coming from the terminal carbon-atom positions in the respective terminal ribose "rings.

You should examine a diagram to assure yourself that you fully understand the mechanics of mRNA synthesis. This, like so many biological processes, is provided by the phosphate bonds in the nucleoside triphosphates themselves.

As transcription occurs, it does so, as stated, along a single strand of DNA. Be aware, however, that the entire DNA molecule does not uncoil and separate into complementary strands; this only happens in the direct vicinity of transcription. As a result, you can visualize a "transcription bubble" moving along the DNA molecule. This is like an object that moves along a zipper that is being unzipped just ahead of the object by one mechanism while a different mechanism re-zips the zipper in the object's wake.

Finally, when the mRNA has reached its required length and form, the termination phase gets underway. In bacteria, this can happen in two general ways. In one of these, the termination sequence is transcribed, generating a length of mRNA that folds back in on itself and thereby "bunches up" as the RNA polymerase continues to do its job.

These folded sections of mRNA are often referred to as hairpin strands, and they involve complementary base pairing within the single-stranded but contorted mRNA molecule. This video provides a review of these steps.

You can stop watching the video at Improve this page Learn More. Skip to main content. Search for:. You can also walk through the steps of transcription in this link. Try It. Did you have an idea for improving this content? The newly formed mRNA copies of the gene then serve as blueprints for protein synthesis during the process of translation. Further Exploration Concept Links for further exploration translation transcription unit gene expression frameshift mutation nonsense mutation RNA DNA enhancer promoter differentiation gene expression transcription factor intron exon chromatin histones mutation helicase transcriptome phosphate backbone poly-A tail nuclear pore primase TATA box hairpin loop mRNA DNA polymerase mRNA chromatin remodeling cis-regulatory element RNA polymerase catabolite repression methylation.

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