Cloverleaf-like two-dimensional (A) and L-shaped three-dimensional (B) representations of tRNA structure. The molecule shown is the E. coli tRNAAla with GGC anticodon and the 3G:U72 "wobbling" base pair that determine the identity of all Ala tRNAs across all species . Because in the ancestral tRNAs with complementary anticodons the second bases in the acceptor are also complementary to each other [6, 22], they are shown enlarged and boxed. The L-shaped tRNA consists of two halves, the minihelix (acceptor stem plus Tψ C arm), and the 'dumbbell' (anticodon arm plus D arm). The hypothetical aminoacylating ribozyme is shown by dotted line on the right (adapted from [12, 24]).