Review Question - QID 214686

This mutation affects leucyl-tRNA synthetase, as evidenced by the different Western blot bands between mutated and control enzymes, and results in the attachment of valine instead of leucine. Leucyl-tRNA synthetase normally attaches leucine to the appropriate tRNA’s 3’ CCA tail.

Translation occurs through the interaction of ribosomes and mRNA. Transfer RNAs (tRNA) carry their appropriate amino acids and deliver them to the growing polypeptide chain sequentially according to the mRNA sequence. First, the tRNAs need to be “charged” with the correct amino acid by aminoacyl-tRNA synthetases. After recognizing the correct tRNA D-arm, the aminoacyl-tRNA synthetase catalyzes the following reaction: tRNA + ATP + amino acid -> amino acid-tRNA + AMP + PPi. The amino acid is covalently linked to the 3’ CCA tail of tRNA. There are no correction mechanisms if an incorrect amino acid is “charged” onto a tRNA, so the amino acid would be erroneously attached to the polypeptide chain.

Incorrect Answers:
Answer 1: The anti-codon loop is used to pair with a codon of mRNA in a complementary, antiparallel fashion. Wobble is a phenomenon where the first 2 nucleotide positions are sufficient for specifying an amino acid.

Answer 3: The D-arm is used for aminoacyl-tRNA synthetase recognition. It often contains dihydrouridine.

Answer 4: The T-arm is used for ribosome recognition. It contains a sequence of TΨC (Ψ = pseudouridine).

Answer 5: The variable arm exists in a range of nucleotide lengths and is sometimes absent. It is found between the anti-codon loop and T-arm. It facilitates variations in tRNA shape.

Bullet Summary:
Amino acids bind to tRNA at the 3’ CCA tail.