Question

Write the polarity of the template strand and coding strand. Write three regions of the transcription unit.

Answer 1

The process of copying genetic information from one strand of the DNA into RNA is termed as transcription. The principle of complementarity governs the process of transcription. In transcription only a segment of DNA and only one of the strands get copied into RNA.

Complete answer:
When referring to DNA transcription, the coding strand is the base sequence of DNA whose base sequence corresponds to the base sequence of the new mRNA strand formed by process of transcription.
The DNA strand that mRNA is built from is called the template strand because it serves as a template for transcription. It is also called the antisense strand. The template strand runs in a 3’ to 5’ direction.
The strand of DNA not used as a template for transcription is called the coding strand, because it corresponds to the same sequence as the mRNA that will contain the codon sequences necessary to build proteins. The coding strand is also called the sense strand. The coding strand runs in a 5’ to 3’ direction.
Transcription is carried out by an enzyme called RNA polymerase and a number of accessory proteins called transcription factors. The sequences necessary for transcription contain a promoter, an RNA coding sequence, and a terminator. The transcription factors can bind to specific DNA sequences like enhancer and promoter to recruit RNA polymerase to an appropriate transcription site.

Promoter region: these are the DNA sequences that define from where transcription of a gene by RNA polymerase begins. This region is located directly upstream or at the 5’ end of the transcription initiation site. Many eukaryotic genes have a conserved promoter sequence called the TATA box, located 25-30 base pairs upstream of the transcription start site.
Structural genes are typically viewed as those containing sequences of DNA corresponding to the amino acids of a protein that will be produced. Structural gene products include enzymes and structural proteins. In this region transcription takes place.

Terminator region: A transcription terminator is a section of nucleic acid sequence that marks the end of a gene in DNA during transcription. This sequence mediates transcriptional termination by providing signals in the newly synthesized RNA which release the newly transcribed RNA from the transcriptional complex. The release of the transcriptional complex frees RNA polymerase and related transcriptional machinery.

Note: The coding sequences or expressed sequences are defined as exons. Exons are said to be those sequences that appear in mature or processed RNA. The exons are interrupted by introns. The introns do not appear in mature or processed RNA.