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Biology Question 110 – NEET-UG 2024

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A transcription unit in DNA is defined primarily by the three regions in DNA and these are with respect to upstream and down stream end;

Recall the fundamental components required for gene transcription in DNA.

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Ninja Strategy•Component Type Elimination

Quickly eliminate options that include non-DNA components (like proteins or mobile elements) or components not universally defining a transcription unit, leaving the correct set of DNA regions.

Step 1: Define a Transcription Unit✦ Active

A transcription unit in DNA is a segment of DNA that is transcribed into an RNA molecule. It is typically composed of three main regions:

1. Promoter: The binding site for RNA polymerase, located upstream of the structural gene.

2. Structural gene(s): The region of DNA that codes for the RNA molecule (mRNA, tRNA, or rRNA).

3. Terminator: The sequence that signals the end of transcription, located downstream of the structural gene.

💡 Teacher's Secret Hint

Remember that the question asks for 'regions in DNA', which excludes proteins or mobile genetic elements.

Step 2: Evaluate the Options○ Expand

Let's examine each option based on the definition of a transcription unit:

(1) Structural gene, Transposons, Operator gene: Transposons are mobile genetic elements, not a standard part of a transcription unit. Operator gene is a regulatory sequence, but not one of the three primary defining regions in all transcription units.

(2) Inducer, Repressor, Structural gene: Inducer and Repressor are molecules (often proteins or small molecules) that regulate gene expression, not DNA regions themselves.

(3) Promotor, Structural gene, Terminator: This option correctly lists the three essential DNA regions that constitute a transcription unit.

(4) Repressor, Operator gene, Structural gene: Repressor is a protein, not a DNA region. Operator gene is a regulatory DNA sequence, but the core components are promoter, structural gene, and terminator.

💡 Teacher's Secret Hint

Distinguish between DNA sequences and regulatory proteins/molecules.

Step 3: Conclusion○ Expand

Based on the definition, option (3) accurately describes the three primary regions of a transcription unit in DNA.

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