Final answer:
tRNAs contain unusual bases like dihydrouracil in the DHU arm and pseudouridine in the TΨC arm, which are important for their recognition and function. Inosine is a modified base created by the deamination of A34, which is key for the correct interaction of tRNA with mRNA. These bases and modifications vary across the domains of life due to evolutionary differences.
Step-by-step explanation:
tRNA molecules are crucial for the translation process in cells, acting as the link between the genetic code in mRNA and the amino acid sequence of proteins. During this process, tRNAs use anticodon loops to recognize specific codons on the mRNA. However, the structure of tRNA includes arms that can contain unusual bases which play significant roles in its function and recognition. One example of an unusual base is dihydrouracil, found within the dihydrouridine (DHU) arm of tRNA. This nucleotide is not found in RNA or DNA but is exclusive to tRNA and is important for the recognition of the appropriate aminoacyl-tRNA synthetase. Another example is pseudouridine (Ψ), which features an unusual carbon-carbon bond between the base and the sugar. This base is found within the ribothymidine-pseudouridine (TΨC) arm and helps in binding the aminoacyl-tRNA to the ribosomal surface during protein synthesis.
In addition, many tRNAs undergo base modifications after their initial synthesis. For example, in eukaryotic tRNAs, a significant modification is the deamination of adenosine at position 34 to form inosine (I34), a process catalyzed by adenosine deaminases acting on tRNA (ADAT). These base modifications are critical for ensuring the correct matching of tRNA anticodons with mRNA codons, and can vary across different domains of life due to evolutionary divergences in tRNA gene composition and modification patterns.