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.
Read the following statements about translation:
A. In the first phase, amino acids are activated in the presence of ATP.
B. Activated amino acids are linked to their cognate tRNA, a process called aminoacylation of tRNA.
C. If two charged tRNAs are brought close enough, the formation of a phosphodiester bond between them is favoured energetically.
D. The presence of a catalyst would enhance the rate of peptide bond formation.
Choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → A, B and D only
The passage says that forming a peptide bond needs energy. NCERT explains how the cell meets this need: in the first phase, amino acids are activated with ATP and attached to their own tRNA. This is called charging of tRNA, or aminoacylation of tRNA.
A. In the first phase, amino acids are activated in the presence of ATP. — True. Activation by ATP supplies the energy for the later peptide bond.
B. Activated amino acids are linked to their cognate tRNA, a process called aminoacylation of tRNA. — True. This is also called charging of tRNA.
C. If two charged tRNAs are brought close enough, the formation of a phosphodiester bond between them is favoured energetically. — False. Two charged tRNAs brought close together favour the formation of a peptide bond between their amino acids. Phosphodiester bonds link nucleotides in a nucleic acid, not amino acids.
D. The presence of a catalyst would enhance the rate of peptide bond formation. — True. In the ribosome, the 23S rRNA of bacteria acts as this catalyst (a ribozyme).
So A, B and D are correct.
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. If two such charged tRNAs are brought close enough, the formation of peptide bond between them would be favoured energetically. The presence of a catalyst would enhance the rate of peptide bond formation.”