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Team:MoWestern Davidson/tRNA structure
From 2009.igem.org
tRNA Structure
The Cloverleaf Model
The structure of tRNA molecules is often represented by showing how stems and loops are formed by base pairing within a two-dimensional context—useful for depicting secondary structure, but unable to show three dimensional folding. Each tRNA molecule consists of five arms, and each, with the exception of the acceptor arm, contains both stems and loops. A stem is formed by self base-pairing along the RNA strand, and loops are formed from non-paired nucleotides. The 3′ terminus of the TRNA strand protrudes beyond the 5′ terminus by several nucleotides, but the 5′ terminus is base-paired. The appropriate amino acid is connected to the 3′ terminus by an amino acyl tRNA synthetase, an enzyme that uses the unique structural motif of each tRNA to consistently pair it with its designated amino acid. Moving from the 3′ terminus in the 5′ direction, the TΨC arm is encountered. It is so named because of the presence of the sequence 5′-TΨC-3′, where Ψ stands for the base pseudouracil, an isomer of uracil formed from post-transcriptional modification. Continuing in the 5′ direction, the variable loop is encountered. This portion of the tRNA family of molecules shows high size variation, from only a few nucleotides to well over a dozen. Next is the anticodon arm, which contains the anticodon itself. The anticodon recognizes its mRNA complement, and may contain a wobble base-pairing at the 5′ end residue of the anticodon. This wobble base-pairing often utilizes the abundant assortment of non-standard nucleotides. The final arm before the 5&prime' terminus is the D arm. It contains the D base, or dihydrouracil.
The Spacial tRNA Structural Motif
Base-pairing between arms stabilizes the structure of the tRNA molecule into a L-shape. The acceptor arm is positioned at one and of the L, and the anticodon at the other. The size and sequence of each arm influences the spacial structure of the tRNA, and allows enzymes responsible for maintaining function to recognize each tRNA.
