Translation, the Genetic Code, and Protein Quality Control
From Codons to Functional Proteins
Translation overview
Translation is a highly coordinated process in which the ribosome decodes mRNA, verifies codon-anticodon pairing, catalyzes peptide bond formation, and responds to elongation control signals and quality-control checkpoints.
Core concepts
Translation control layers
Initiation control
- Often rate-limiting
- Sensitive to nutrient and stress signaling
Elongation control
- Affected by codon usage and tRNA availability
- Can regulate co-translational folding
Misfolding and disease
Errors in translation, folding, or degradation can cause toxic protein accumulation, loss of function, or proteotoxic stress.
What ensures that each tRNA is linked to the correct amino acid before translation?
Charging fidelity is established by aminoacyl-tRNA synthetases, which edit and select the correct amino acid-tRNA pair.
Correct answer: Aminoacyl-tRNA synthetase specificity
Why can codon usage affect protein expression?
Codon bias influences elongation speed, co-translational folding, and translational output.
Correct answer: Different codons can be translated at different rates depending on tRNA abundance and decoding efficiency
Quality-control pathways
| Pathway | Role |
|---|---|
| Nonsense-mediated decay | Removes faulty mRNAs with premature stop codons |
| No-go decay | Addresses stalled ribosomes |
| Nonstop decay | Rescues ribosomes on mRNAs lacking stop codons |
| Ubiquitin-proteasome system | Degrades unwanted proteins |
Which statement best describes the ribosome's catalytic role?
The peptidyl transferase center is a ribozyme, with rRNA catalyzing peptide bond formation.
Correct answer: It catalyzes peptide bond formation through rRNA-dependent chemistry
What is proteostasis?
Proteostasis integrates chaperones, translation, and degradation pathways.
Correct answer: The cellular network that maintains protein synthesis, folding, trafficking, and degradation balance