Understanding Why DNA Transcription is Necessary
DNA is used as a template to make mRNA, which contains the information to make a polypeptide.
DNA is indeed an information storage unit. For genes to be expressed, the information in them must be accessed at the molecular level. Rather than accessing the information directly, however, a working copy of the DNA, composed of RNA, is made.
This happens by the process of transcription, in which a DNA sequence is copied into an RNA sequence.
At the Molecular Level, a Gene Can Be Transcribed and Produces a Functional Product
A molecular definition of a gene– organized unit of DNA sequences that enables a segment of DNA to be transcribed into RNA and results in the formation of a functional product.
When a structural gene is transcribed, an mRNA is made that specifies the amino acid sequence of a polypeptide.
The polypeptide is considered to be the functional product, while the mRNA is an intermediary in polypeptide synthesis.
Boundaries of Transcription
Transcription begins near a site in the DNA called the promoter.
The terminator specifies the end of transcription.
These 2 sequences provide the boundaries for RNA to be synthesized within a defined location.
The DNA is transcribed into mRNA from the end of the promoter through the coding sequence to the terminator.
Stages of Transcription
Transcription occurs in three stages called initiation, elongation, and termination, during which proteins interact with DNA sequences.
The promoter functions as a recognition site for sigma factor. RNA polymerase is bound to sigma factor, which causes it to recognize the promoter. Following binding, the DNA is unwound into a bubble known as the open complex.
Elongation/Synthesis of the RNA Transcript
RNA polymerase synthesizes the RNA transcript during the elongation stage.
Sigma factor is released and RNA polymerase slides along the DNA in an open complex to synthesize RNA.
The DNA strand that is used as a template for RNA synthesis is called the template or noncoding strand. The opposite DNA strand is called the coding strand.
When RNA polymerase reaches the terminator, it and the RNA transcript dissociate, (Disconnect or separate), from the DNA.