12. Which of the following mRNA molecules would form the most stable stem-loop
structure?
a. 5’…GGCUU……UUCGG…3′
b. 5’…GGCUU……AAGCC…3′
c. 5’…GGCUU……GGCUU…3′
d. 5’…GGCUU……CCGAA…3′
Most Stable mRNA Stem-Loop: CSIR NET Question Solved
Option B forms the most stable mRNA stem-loop structure among the choices. Stability depends on Watson-Crick base pairing in the stem, with GC pairs (3 hydrogen bonds) far stronger than AU pairs (2 hydrogen bonds); mismatches or non-canonical pairs destabilize it.​
Option Analysis
Each option has 5′ GGCUU paired against the 3′ sequence in a hairpin stem.
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Option A (5’…GGCUU……UUCGG…3′): Forms G-U, G-U, C-C, U-U, U-G pairs. Zero Watson-Crick matches; all mismatches make it highly unstable.​
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Option B (5’…GGCUU……AAGCC…3′): Perfectly complementary: G-C, G-C, C-G, U-A, U-A. Three GC pairs provide maximum stability.​
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Option C (5’…GGCUU……GGCUU…3′): Self-complementary but yields G-U, G-U, C-C, U-G, U-G. No Watson-Crick pairs; unstable due to wobble/mismatches.​
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Option D (5’…GGCUU……CCGAA…3′): Partial pairing: G-A, G-A, C-G, U-C, U-C. Only one GC pair; four mismatches reduce stability.​
In CSIR NET Life Sciences preparation, understanding the most stable mRNA stem-loop structure is crucial for molecular biology questions on RNA secondary structure and stability. Stem-loops (hairpins) regulate mRNA degradation, translation, and gene expression, with stability driven by stem base pairing. This guide solves a classic MCQ while explaining factors like GC content for exam success.​
Stem-Loop Basics
RNA stem-loops feature a double-stranded stem from complementary inverted repeats and a single-stranded loop. Stability increases with:
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More base pairs in the stem.
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GC pairs over AU (3 vs. 2 H-bonds).
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Strong closing base pairs near the loop.​
Loops of 4-7 nt are optimal; mismatches (bulges) destabilize.​
Detailed Option Breakdown
| Option | Sequence Pairing (5′-3′) | WC Pairs | GC Pairs | Stability |
|---|---|---|---|---|
| A | G-U, G-U, C-C, U-U, U-G | 0/5 | 0 | Lowest |
| B | G-C, G-C, C-G, U-A, U-A | 5/5 | 3 | Highest |
| C | G-U, G-U, C-C, U-G, U-G | 0/5 | 0 | Low |
| D | G-A, G-A, C-G, U-C, U-C | 1/5 | 1 | Moderate ​ |
Option B wins due to perfect complementarity and high GC content, mimicking stable natural hairpins like UUCG tetraloops.​
Exam Tips
Practice predicting pairings manually or via tools like mfold. Focus on CSIR NET topics: RNA structure affects half-life (e.g., histone mRNA 3′ stem-loop). Revise thermodynamics: ΔG favors GC-rich stems.​
