Transcription is the first part of gene expression - making DNA into functional proteins. It occurs in the nucleus of cells. During transcription, information from DNA is transcribed into messenger RNA (mRNA). In a process called translation, mRNA is translated into a string of amino acids that become folded into proteins who continue to do a multitude of functions in the cell.
There are three main steps in transcription: initiation, elongation and termination.
Initiation: The process of transcription is initiated when an RNA polymerase enzyme binds to a region of DNA at a promoter sequence. This binding cause the DNA double helix to unwind and one of the two DNA strands is transcribed into mRNA
Elongation: RNA polymerase reads the antisense strand and adds nucleotides complementary to the antisense strand at 3’ end of the growing mRNA transcript. The mRNA strand is complementary to the antisense strand and therefore identical to the opposite strand (sense strand).
Termination: This phase occurs when RNA polymerase reaches a specific sequence on the DNA, called a termination sequence. This is a sequence of nucleotides that signal to the polymerase to dissociate from the DNA and release the mRNA transcript. The mRNA transcript then exits the nucleus and is translated into protein.
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