​Precise recognition of tRNAs by their cognate aminoacyl-tRNA synthetases is crucial for the fidelity of protein synthesis. In the context of the aminoacylation of tRNA^Ala with its cognate aminoacyl-tRNA synthetase (AlaRS), and based on the studies on the molecules of Escherichia coli origin, the following statements are made.​

​Which one of the statements is INCORRECT?​

​

Correct option is A

Explanation-

Option a - "Anticodon of  tRNA^​Ala  makes important contribution to the specificity of its aminoacylation by AlaRS." - INCORRECT
In E. coli, AlaRS does not recognize the anticodon of tRNA^​Ala .Recognition is entirely dependent on the acceptor stem, especially the G3:U70 wobble pair. Experimental mutation of the anticodon does not affect aminoacylation, proving anticodon is not involved. This is the incorrect statement, hence the correct answer.
Option b - "Mutational analyses have shown that for aminoacylation of the tRNA^​Ala by AlaRS, the presence of a wobble pair in the acceptor stem (G3:U70) is the most crucial element." - CORRECT
The G3:U70 wobble pair is the major identity element for AlaRS. Mutation of this pair to standard Watson-Crick pairs (like G-C or A-U) abolishes recognition by AlaRS. This has been shown via mutagenesis and in vitro aminoacylation assays.
Option c - "Aminoacylation of tRNA^​Ala by AlaRS occurs even if the anticodon of tRNA^Ala is mutated." - CORRECT
As stated, AlaRS ignores the anticodon. Even if the anticodon is mutated (e.g., changed to that of tRNA^Phe , AlaRS will still aminoacylate it, provided the G3:U70 pair is intact.
Option d - "A microhelix lacking a cloverleaf structure and harboring only the acceptor stem sequence of the tRNA^​Ala is specifically aminoacylated by AlaRS." - CORRECT
A synthetic microhelix mimicking the acceptor stem of tRNA^​Ala, with the G3:U70 pair, is sufficient for recognition and aminoacylation by AlaRS. This shows that no other regions (like the D-loop or anticodon loop) are necessary for AlaRS activity.

Correct Answer: Option a - "Anticodon of tRNA​^Ala makes important contribution to the specificity of its aminoacylation by AlaRS."