GATE BT 2018 • Q14 MCQ • 1 Mark

Section 3: Genetics, Cellular and Molecular Biology

DNA replication, transcription, translation

Subtopic: Fundamentals of DNA replication, transcription, translation

Question Statement:

If a segment of a sense strand of DNA is 5-ATGGACCAGA-3, then the resulting RNA sequence after transcription is

Options:

  • (A) 5-AGACCAGGTA-3
  • (B) 5-UCUGGUCCAU-3
  • (C) 5-UACCUGGUCU-3
  • (D) 5-AUGGACCAGA-3

Official Answer Key:

D

Step-by-Step Solution & Explanation

### **Official Solution & Step-by-Step Derivation (GATE BT 2018 Q.14)** **1. Governing Concept & Question Classification**: - **Section**: BT - **Question Type**: **MCQ** (1 Mark) - **Topic**: Molecular Biology (Transcription / Strand Nomenclature) **2. Detailed Step-by-Step Derivation**: - In transcription terminology: - **Sense strand** = **Coding strand** = **Non-template strand** (+ strand). - **Antisense strand** = **Template strand** (- strand), which is read $3' o 5'$ by RNA polymerase. - The resulting mRNA transcript is identical in sequence and polarity to the **sense strand**, with the single biochemical exception that thymine (T) in DNA is replaced by uracil (U) in RNA: $ ext{Sense DNA}: \quad 5' ext{--ATGGACCAGA--}3'$ $ ext{Template DNA}: \quad 3' ext{--TACCTGGTCT--}5'$ $ ext{mRNA Transcript}: \quad 5' ext{--AUGGACCAGA--}3'$ - **Option-by-Option Evaluation**: - **Option (A) [INCORRECT]**: $5' ext{--UACCUGGUCU--}3'$ is the complementary antisense RNA, not the sense-derived mRNA. - **Option (B) [INCORRECT]**: $5' ext{--AGACCAGGUA--}3'$ represents an incorrect scrambled/reversed sequence. - **Option (C) [INCORRECT]**: $5' ext{--UCUGGUCCAU--}3'$ is the reverse complement of the mRNA. - **Option (D) [CORRECT]**: $5' ext{--AUGGACCAGA--}3'$ directly replaces each T of the sense strand with U while preserving $5' o 3'$ directionality. **3. Final Answer / Verification Summary**: - **Official GATE Answer Key**: **D** - **Scoring Criteria**: +1.0 Mark (Negative marking: -0.33 marks).

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