Q.37 Two RNAs shown below were used separately as templates in an in vitro
translation system, which can generate proteins in all possible reading frames.
RNA1: 5′ − (AG)n − 3′
RNA2: 5′ − (AAG)n − 3′
The 𝑅𝑁𝐴1 translated product contained Arg and Glu.
The 𝑅𝑁𝐴2 translated product contained Arg, Glu, and Lys.
Which one of the following codons directs the incorporation of Arg?
(A) AAG
(B) AGA
(C) GAA
(D) GAG
AGA codes for arginine in this in vitro translation experiment with repeating RNA templates.
RNA1 Translation Analysis
RNA1 (5′-(AG)n-3′) produces repeating AGAGAGA… sequences. In all three reading frames, possible codons include AGA (arginine), GAG (glutamic acid), and AGG (arginine), but experimental products contain only Arg and Glu. This confirms AGA and GAG as the key codons, with AGA directing Arg incorporation.
RNA2 Translation Analysis
RNA2 (5′-(AAG)n-3′) yields AAGAAGAAG… repeats. Reading frames produce AAG (lysine), AGA (arginine), and GAA (glutamic acid). Products contain Arg, Glu, and Lys, matching these assignments exactly.
Option Evaluation
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(A) AAG: Codes for lysine, present only in RNA2 products, not RNA1.
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(B) AGA: Codes for arginine, appears in both RNAs, matching RNA1’s Arg.
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(C) GAA: Codes for glutamic acid (Glu), not Arg.
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(D) GAG: Codes for glutamic acid (Glu), not Arg.
In CSIR NET Life Sciences preparation, mastering (AG)n (AAG)n RNA translation Arg codon questions tests genetic code and reading frame knowledge. This in vitro translation problem reveals how repeating RNAs generate specific polypeptides across frames, crucial for molecular biology exams.
Reading Frames in Repeating RNAs
Polymeric RNAs like 5′-(AG)n-3′ create periodic codons in three frames:
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Frame 1: AGA-GAG-AGA… (Arg-Glu repeat)
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Frame 2: GAG-AGA-GAG…
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Frame 3: AG-AGA-GAG… (shorter, but overlaps)
RNA1 yields only Arg and Glu, confirming AGA (Arg) and GAG/GAA (Glu). For 5′-(AAG)n-3′:
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Frame 1: AAG-AAG… (Lys)
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Frame 2: AGA-GAA… (Arg-Glu)
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Frame 3: GAA-AGA… (Glu-Arg)
Lys appears uniquely in RNA2 via AAG.
Genetic Code Confirmation
Standard table verifies:
| Codon | Amino Acid |
|---|---|
| AAG | Lys |
| AGA | Arg |
| GAA | Glu |
| GAG | Glu |
This matches experimental polypeptides perfectly.
Exam Strategy Tip
For CSIR NET, list all frame codons first, then match to given amino acids. Eliminate options absent in RNA1 (like AAG/Lys).
