Biology Reference
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Figure 2.6 A tRNA molecule has a complex shape. Bases are numbered from 1 to 76. A few bases
that are present in almost all tRNA molecules are identified by letters. The Greek letter ψ is a symbol
for the unusual base pseudouridine. The amino-acid attachment site is at the 3 end of the tRNA
and the anticodon (the genetic code that determines the amino-acid order) is at the bottom of the
diagram. The anticodon will base-pair in a complementary manner with the mRNA codon.
one, aminoacyl synthetase is found for each amino acid. However, there are fewer
aminoacyl synthetases than there are codons for amino acids. Thus, aminoacyl
synthetases must recognize more than one codon. The wobble hypothesis sug-
gests that base pairing is most critical with the first two bases of the three-base
codon but that pairing is extremely flexible in the third position.
Gene translation in eukaryotes usually involves multiple ribosomes process-
ing along a single mRNA molecule. Thus, after 25 amino acids have been
joined together into a polypeptide, the AUG initiation codon is free of the first
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