A transfer RNA with a UGU anticodon is enzymatically...

A transfer RNA with a UGU anticodon is enzymatically conjugated to $^{14}$ C-labeled cysteine. The cysteine unit is then chemically modified to alanine (with the use of Raney nickel, which removes the sulfur atom of cysteine). The altered aminoacyl-tRNA is added to a protein-synthesizing system containing normal components except for this tRNA. The mRNA added to this mixture contains the following sequence: $$5^{\prime}-U U U U G C C A U G U U U G U G C U-3^{\prime}$$ What is the sequence of the corresponding radiolabeled peptide?

Key Concepts

Mechanism of Protein Synthesis

Protein synthesis (translation) is the process by which ribosomes read mRNA codons sequentially and, with the help of appropriately charged tRNAs, build a polypeptide chain. The accuracy of this process depends on correct codon-anticodon pairing and proper aminoacylation of tRNA molecules.

Chemical Modification of Aminoacyl-tRNA

Chemical modification of an aminoacyl-tRNA involves altering the amino acid attached to the tRNA after enzymatic charging. Such modifications, like converting a charged cysteine to an alanine, are used experimentally to reassign codon identities or to study aspects of protein synthesis.

Genetic Code

The genetic code is the set of rules by which sequences of three nucleotides (codons) in mRNA specify corresponding amino acids. This universal code is the basis for translating nucleotide sequences into functional proteins.

Aminoacylation (tRNA Charging)

Aminoacylation is the enzymatic process by which an amino acid is covalently attached to its corresponding tRNA by an aminoacyl-tRNA synthetase. This charging step is critical for translating the genetic code accurately into a polypeptide sequence.

Transfer RNA (tRNA) Structure and Function

tRNAs are adaptor molecules in protein synthesis that carry specific amino acids and contain an anticodon loop. The anticodon, a set of three nucleotides, base?pairs with complementary codons on the mRNA, ensuring that the correct amino acid is incorporated into the growing polypeptide.

Anticodon–Codon Pairing

During translation, the anticodon on a tRNA recognizes and binds to a complementary codon on the mRNA via Watson–Crick base pairing. This specific interaction is essential for maintaining the fidelity of protein synthesis by matching each codon with its appropriate amino acid.

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