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Protein Synthesis
How are amino acids assembled during translation?
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GPT-5 mini
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Translation assembles amino acids into a polypeptide chain by reading the mRNA codons and using charged tRNAs as adaptors. Key points and steps:
- Charging tRNAs (before translation): each amino acid is covalently attached to its specific tRNA by an aminoacyl‑tRNA synthetase. This uses ATP and makes a high‑energy aminoacyl‑tRNA (amino acid linked to the tRNA 3′ end).
- Initiation: the small ribosomal subunit, initiator tRNA (carrying Met in eukaryotes or fMet in bacteria) and initiation factors bind the mRNA and locate the start codon (AUG). The large subunit joins to form a functional ribosome with three sites: A (aminoacyl), P (peptidyl), and E (exit).
- Elongation (repeated cycle):
1. Codon recognition: a charged tRNA whose anticodon complements the mRNA codon enters the A site (delivery aided by elongation factors and GTP).
2. Peptide bond formation: the ribosome’s peptidyl transferase activity (an rRNA catalytic center) catalyzes formation of a peptide bond between the carboxyl end of the growing peptide (on the tRNA in the P site) and the amino group of the new amino acid (on the A‑site tRNA). This transfers the peptide to the tRNA in the A site.
3. Translocation: the ribosome moves one codon along the mRNA (requires GTP and elongation factors), shifting the peptidyl‑tRNA to the P site and the empty tRNA to the E site to be released.
- Termination: when a stop codon enters the A site, release factors promote hydrolysis of the bond between the polypeptide and the tRNA, releasing the completed protein and allowing ribosome subunits to dissociate.
Other important details:
- Translation proceeds N‑terminus → C‑terminus.
- Codon–anticodon pairing sets the amino acid order; wobble at the third codon position allows some tRNAs to read multiple codons.
- Peptide bond formation is a condensation reaction catalyzed by the ribosome; energy was stored in the aminoacyl‑tRNA linkage formed during charging.
That is how amino acids are assembled into a protein during translation.
- Charging tRNAs (before translation): each amino acid is covalently attached to its specific tRNA by an aminoacyl‑tRNA synthetase. This uses ATP and makes a high‑energy aminoacyl‑tRNA (amino acid linked to the tRNA 3′ end).
- Initiation: the small ribosomal subunit, initiator tRNA (carrying Met in eukaryotes or fMet in bacteria) and initiation factors bind the mRNA and locate the start codon (AUG). The large subunit joins to form a functional ribosome with three sites: A (aminoacyl), P (peptidyl), and E (exit).
- Elongation (repeated cycle):
1. Codon recognition: a charged tRNA whose anticodon complements the mRNA codon enters the A site (delivery aided by elongation factors and GTP).
2. Peptide bond formation: the ribosome’s peptidyl transferase activity (an rRNA catalytic center) catalyzes formation of a peptide bond between the carboxyl end of the growing peptide (on the tRNA in the P site) and the amino group of the new amino acid (on the A‑site tRNA). This transfers the peptide to the tRNA in the A site.
3. Translocation: the ribosome moves one codon along the mRNA (requires GTP and elongation factors), shifting the peptidyl‑tRNA to the P site and the empty tRNA to the E site to be released.
- Termination: when a stop codon enters the A site, release factors promote hydrolysis of the bond between the polypeptide and the tRNA, releasing the completed protein and allowing ribosome subunits to dissociate.
Other important details:
- Translation proceeds N‑terminus → C‑terminus.
- Codon–anticodon pairing sets the amino acid order; wobble at the third codon position allows some tRNAs to read multiple codons.
- Peptide bond formation is a condensation reaction catalyzed by the ribosome; energy was stored in the aminoacyl‑tRNA linkage formed during charging.
That is how amino acids are assembled into a protein during translation.
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