Read the following statements about translation:
A. In the first phase, amino acids are activated in the presence of ATP and linked to their cognate tRNA, a process called charging of tRNA.
B. In bacteria, the 23S rRNA of the ribosome acts as the enzyme (ribozyme) for the formation of peptide bonds.
C. When the large subunit of the ribosome encounters an mRNA, the process of translation of the mRNA to protein begins.
D. A translational unit in mRNA is the sequence of RNA flanked by the start codon (AUG) and the stop codon, and it codes for a polypeptide.
Choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → A, B and D only
Translation is the process in which amino acids are joined into a polypeptide. The order of the amino acids is set by the sequence of bases in the mRNA. Two adjacent amino acids are joined by a peptide bond, and making this bond needs energy. The ribosome is the cell’s factory for this work. In its inactive state it exists as two subunits, a large one and a small one.
Statement A: In the first phase, amino acids are activated in the presence of ATP and linked to their cognate tRNA, a process called charging of tRNA. — True. Because a peptide bond needs energy, amino acids are first activated using ATP. Each amino acid is then attached to its own (cognate) tRNA. This step is called charging of tRNA, or aminoacylation of tRNA.
Statement B: In bacteria, the 23S rRNA of the ribosome acts as the enzyme (ribozyme) for the formation of peptide bonds. — True. A ribozyme is an RNA that works as an enzyme. In bacteria, the 23S rRNA of the ribosome is the catalyst that forms the peptide bond.
Statement C: When the large subunit of the ribosome encounters an mRNA, the process of translation of the mRNA to protein begins. — False. Translation begins when the small subunit meets the mRNA, not the large subunit. The large subunit has the two sites where the incoming amino acids bind and come close enough to form a peptide bond.
Statement D: A translational unit in mRNA is the sequence of RNA flanked by the start codon (AUG) and the stop codon, and it codes for a polypeptide. — True. The part of the mRNA between the start codon AUG and a stop codon is read into one polypeptide. The extra sequences outside it, at the 5′ and 3′ ends, are the untranslated regions (UTRs).
NCERT Extract:
Translation – “… Formation of a peptide bond requires energy. Therefore, in the first phase itself amino acids are activated in the presence of ATP and linked to their cognate tRNA – a process commonly called as charging of tRNA or aminoacylation of tRNA to be more specific. … In its inactive state, it exists as two subunits; a large subunit and a small subunit. When the small subunit encounters an mRNA, the process of translation of the mRNA to protein begins. … The ribosome also acts as a catalyst (23S rRNA in bacteria is the enzyme- ribozyme) for the formation of peptide bond. A translational unit in mRNA is the sequence of RNA that is flanked by the start codon (AUG) and the stop codon and codes for a polypeptide.”