Promoters, Terminators & Gene Polarity — NEET Biology
📚 Practice ConceptThe promoter and terminator flank the structural gene in a transcription unit. The promoter is said to be located towards 5'-end (upstream) of the structural gene (the reference is made with respect to the polarity of coding strand). It is a DNA sequence that provides binding site for RNA polymerase, and it is the presence of a promoter in a transcription unit that also defines the template and coding strands. By switching its position with terminator, the definition of coding and template strands could be reversed. The terminator is located towards 3'-end (downstream) of the coding strand and it usually defines the end of the process of transcription. There are additional regulatory sequences that may be present further upstream or downstream to the promoter. Some of the properties of these sequences shall be discussed while dealing with regulation of gene expression.
Which of the following statements regarding a transcription unit in DNA are NOT correct? S1: The promoter region is located towards the 5'-end (upstream) of the structural gene with respect to the polarity of the coding strand. S2: The template strand serves as the direct coding sequence for the polypeptide, with its sequence being identical to the mRNA. S3: In prokaryotes, a single transcription unit can often be polycistronic, encoding multiple structural genes. S4: The terminator sequence is located towards the 5'-end (upstream) of the coding strand and defines the end of transcription. S5: Regulatory sequences, such as enhancers, are considered primary defining components of a transcription unit along with the promoter, structural gene, and terminator.
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