Which is not a part of a transcription unit in DNA ?

Inducer

The correct answer is Option (2) -Inducer

The process of copying genetic information from one strand of the DNA into RNA is termed as transcription. However, unlike in the process of replication, which once set in, the total DNA of an organism gets duplicated, in transcription only a segment of DNA and only one of the strands is copied into RNA.

A transcription unit in DNA is defined primarily by the three regions in the DNA :
(i) A Promoter
(ii) The Structural gene
(iii) A Terminator

Promoter - This region signals the starting point of transcription and provides a binding site for RNA polymerase.

Terminator - This region signals the end of transcription.

The structural gene - This region contains the sequence that will be transcribed into RNA.

The term "Inducer" generally refers to a substance or molecule that induces or triggers the expression of certain genes. Inducers can activate gene expression by interacting with regulatory elements, but they themselves are not a part of the transcription unit in DNA. Instead, they regulate gene expression by influencing transcription factors or regulatory proteins that control the activation or repression of specific genes.