2. If DNA have sequence 5’-ATGCTCA-3’, is used as template strand, then the sequence of mRNA will be
(1) UAGCUTU                       (2) UACGAGU
(3) UGAGCAU                       (4) TUCGAGT

If DNA has sequence 5’-ATGCTCA-3’, used as template strand, what will be the mRNA sequence?

Question:

If DNA has the sequence 5’-ATGCTCA-3’, and this strand is used as the template strand, what will be the mRNA sequence?

1. UAGCUTU

2. UACGAGU

3. UGAGCAU

4. TUCGAGT

Correct Answer: (3) UGAGCAU

Explanation:

Step 1: Understanding DNA Strands

• The template strand is read in the 3’ to 5’ direction by RNA polymerase.

• Transcription synthesizes mRNA in the 5’ to 3’ direction.

• RNA is complementary to the DNA template, and uracil (U) replaces thymine (T).

Step 2: Reverse the Template Strand

Given:
DNA template strand = 5’-ATGCTCA-3’
But RNA polymerase reads template from 3’ to 5’, so reverse it to read properly:
Template (read 3′ to 5′) = 3’-TCAGTCA-5’

Step 3: Transcribe into mRNA

Now pair each base with its RNA complement:

So, the mRNA sequence is:
5’-UGAGCAU-3’

Final Answer: (3) UGAGCAU

Common Trap (Answer 4)

Option (4) TUCGAGT is incorrect because:

• RNA does not contain thymine (T).

• This option incorrectly uses T instead of U.

Concept Highlight for CSIR NET Aspirants

• Template DNA strand (3’ → 5’) guides the formation of mRNA (5’ → 3’).

• Transcription rules: A → U, T → A, C → G, G → C

• Strand directionality matters — always check 5’ and 3’ ends carefully.

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