Genetics- Transcription and Translation

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The transcription phase of the polypeptide synthesis occurs in the nucleus, where the DNA is located. Transcription is constructed of three steps which are Initiation, elongation and termination. Both the nucleic acids (RNA and DNA) are involved in this stage. The first step of transcription is Initiation:

The enzyme RNA polymerase enters the nucleus alongside the messenger RNA (mRNA). RNA polymerase binds to the promoter then begins to unravel the template and coding strand of the DNA from each other by breaking the hydrogen bonds. Only a small section of DNA is unravelled at a time because only one particular gene at a time is to be transcribed onto the specific mRNA strand. The beginning of the sequence for the gene is determined by the promoter (for example, a sequence of bases which are called ‘TATA’ box), which is a region of DNA.

The elongation step involves the reading of the DNA template strand by mRNA. As the RNA polymerase moves down the specific sequence of bases, starting from where it hooked on the DNA via the promoter. It helps the single RNA nucleotides to match up with the nucleotides on the template DNA strand. This process occurs through complementary base pairing, when Adenine matches Uracil, Thymine with Adenine, Guanine with Cytosine and Cytosine with Guanine. The template strand is complementary to the coding strand and due to this reason the RNA strand is built by using the template strand. This way the exact copy of the coding strand is formed on the mRNA strand, the only difference is Uracil takes the place of Thymine.

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Once the RNA polymerase reaches the terminator, which is a region of the DNA that signals the end of the elongation step. The enzyme (RNA polymerase) unhooks itself from the template DNA strand. This step is the termination step and is the final one for transcription. The DNA is zipped back into its normal shape with the help of RNA polymerase, and the hydrogen bonds are re-formed between the template and coding strands from the point where it had been unzipped. After this, the formed mRNA strand leaves the nucleus through the nuclear pore.


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