Read the passage and answer the following questions:
Translation refers to the process of polymerisation of amino acids to form a polypeptide. The order and sequence of amino acids are defined by the sequence of bases in the mRNA. The amino acids are joined by a bond which is known as a peptide bond. Formation of a peptide bond requires energy.
What binds to the stop codon to terminate translation?
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → Release factor
Translation has three phases: initiation at the start codon, elongation as the ribosome moves from codon to codon, and termination at a stop codon. There is no tRNA for a stop codon, so no amino acid can be added there. Instead, a release factor binds to the stop codon, ends translation and frees the completed polypeptide from the ribosome.
Option (1) tRNA — Incorrect. tRNA brings amino acids by pairing its anticodon with a codon. There are no tRNAs for stop codons, so tRNA cannot bind there.
Option (2) Ribosome — Incorrect. The ribosome moves along the mRNA and catalyses peptide bonds. At the stop codon it is the release factor that binds, and the ribosome lets go of the polypeptide.
Option (3) Release factor — Correct. A release factor binds to the stop codon, terminating translation and releasing the polypeptide.
Option (4) mRNA — Incorrect. mRNA carries the stop codon itself. It is the template being read, not the molecule that binds to the stop codon.
NCERT Extract:
Translation – “… The ribosome moves from codon to codon along the mRNA. Amino acids are added one by one, translated into Polypeptide sequences dictated by DNA and represented by mRNA. At the end, a release factor binds to the stop codon, terminating translation and releasing the complete polypeptide from the ribosome.”
tRNA – the Adapter Molecule – “… For initiation, there is another specific tRNA that is referred to as initiator tRNA. There are no tRNAs for stop codons.”