Multiple Choice
Which organelle is directly responsible for translation (protein synthesis) in eukaryotic cells?
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5. DNA to RNA to Protein
Translation
Multiple Choice
In translation, what happens when a ribosome reaches a stop codon in the mRNA?
A
The ribosome shifts into a new reading frame (frameshift) and continues elongation from the next codon.
B
A tRNA carrying a specialized amino acid binds to the stop codon and adds that amino acid to the growing polypeptide chain.
C
The small ribosomal subunit remains bound to the mRNA and continues scanning until it finds the next start codon to begin translation again immediately.
D
A release factor binds in the A site, catalyzing hydrolysis of the peptidyl-tRNA bond so the completed polypeptide is released and the ribosome dissociates.
Verified step by step guidance1
Understand that translation termination occurs when the ribosome encounters a stop codon (UAA, UAG, or UGA) on the mRNA, which does not code for any amino acid.
Recognize that no tRNA molecules correspond to stop codons, so instead, specialized proteins called release factors bind to the ribosome at the A site where the stop codon is located.
The release factor catalyzes the hydrolysis of the bond between the polypeptide chain and the tRNA in the P site, effectively releasing the newly synthesized polypeptide from the ribosome.
Following polypeptide release, the ribosomal subunits, mRNA, and release factors dissociate from each other, ending the translation process.
This mechanism ensures that translation stops precisely at the stop codon, preventing frameshifts or incorrect elongation of the polypeptide chain.
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