Question

Which is not part of transcription unit?

• A. Promoter
• B. Terminator
• C. Inducer
• D. Structural gene

Answer 1

The correct option is C Inducer

Introduction to transcription unit
Transcription involves synthesis of an RNA strand using the 3’-5’ strand of DNA as the template. The segment of the 3’-5’ template strand or non-coding strand which transcribes into RNA is known as the transcription unit. It is composed of promoter, structural genes and terminator region. Thus, transcription begins at the promoter site and ends at the terminator site.

Promoter region
1) The promoter site is located at the 5’end of the coding/non-template strand, upstream of the initiation codon of the structural gene of the transcription unit.
2) The promoter contains a sequence of nitrogenous bases that provide a site for the RNA polymerase to bind and initiate the process of transcription.

Structural gene
1) Structural gene is the functional unit of inheritance.
2) It is a segment of DNA with a specific sequence of nucleotides that code for a specific polypeptide.
3) Benzer used the term cistron for such a functional segment.

Terminator region
The terminator site defines the end of the transcription unit and is located downstream of the transcription unit on the 3’ end of the coding or non-template strand.The terminator site has two or more stretches of G-C pairs arranged as inverted repeats followed by a polyadenine sequence

Inducer
1) Inducers are chemical compounds that regulate gene expression and favour the transcription of structural genes.
2) They either bind to the repressor molecule and prevent it from binding to the operator.
3) They may also bind to activators and the inducer activator complex binds to activator sequences on the DNA to activate transcription of a specific gene.
4) Inducers are not a part of the transcription unit but regulate its expression.

Final answer
(D) Inducer