The variable arm in tRNA primarily contributes to the stability of the overall tRNA molecule.
While tRNA molecules generally have a conserved structure with four arms (acceptor stem, D arm, anticodon arm, and TΨC arm), the variable arm (also called the extra arm) exhibits significant variation in length and sequence. Located between the anticodon arm and the TΨC arm, it is often shorter and less structured compared to the other arms.
Here's a breakdown of its function and characteristics:
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Variable Structure: The variable arm displays the greatest variability in tRNA structure. It can range from a small loop to a longer arm containing a stem and loop structure.
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Limited Base Pairing: Unlike the other arms, the variable arm often has fewer base pairings. This results in loop-like structures formed by unpaired bases.
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Contribution to Stability: The presence and specific structure of the variable arm play a role in maintaining the overall stability and structural integrity of the tRNA molecule. The precise mechanism by which it contributes to stability isn't fully understood, but it likely involves influencing the folding and flexibility of the tRNA.
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No direct role in codon recognition: The variable arm does not directly participate in the codon-anticodon interaction that is crucial for translation. This function is performed by the anticodon arm.
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Location: Situated between the anticodon arm and the TΨC arm.
In summary, the variable arm, despite its structural variability, is important for the stability of the tRNA molecule, influencing its overall structure and functionality.
