Aminoacyl-tRNA synthetases are responsible for charging tRNAs. Which unique feature ensures that the genetic code is accurately implemented (the 'second genetic code')?
- A The ribosome A-site performs proofreading by comparing the anticodon to the codon before accepting the aminoacyl-tRNA
- B Elongation factor EF-Tu hydrolyzes GTP only when the correct aminoacyl-tRNA:codon interaction occurs
- C Release factors block mismatched tRNAs from entering the ribosome P-site
- D Each synthetase recognizes identity elements on its cognate tRNA (anticodon and acceptor stem sequences) AND has an editing active site that hydrolyzes mischarged tRNA-amino acid bonds ✓
Explanation
The 'second genetic code' refers to the precise recognition of tRNAs by their cognate aminoacyl-tRNA synthetases (aaRS). aaRS use identity elements — specific nucleotides in the anticodon loop, acceptor stem (discriminator base), and sometimes other positions — to distinguish cognate from non-cognate tRNAs. Additionally, class I aaRS have an editing (proofreading) active site distinct from the aminoacylation site: misactivated amino acids (e.g., threonine misactivated on alanine-tRNA) are hydrolyzed before they can cause translational errors. EF-Tu selection also contributes but cannot catch all synthetase errors.
Reference: Harper's Illustrated Biochemistry, 32nd ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
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