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Molecular Basis of Inheritance — BIOLOGY STD 12 Science — Question

Bihar BoardEnglish MediumSTD 12 ScienceBIOLOGYMolecular Basis of Inheritance5 Marks
Question
Explain the steps involved in the elongation of polypeptide chain during its synthesis.
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Answer

  1. An amino acyl tRNA complex reaches the A site and attaches to mRNA codon next to initiation codon with the help of its anticodon. The step requires GTP and an elongation factor.
  2. A peptide bond (-CO-NH-) is established between the carboxylic gp of (-COOH) amino acid attached to tRNA at P site and amino gp (NH) of amino acid attached to tRNA at A-site. The reaction is catalysed by enzyme peptidyl. transferase.
  3. In the process the connection between tRNA and amino acid at the P-site breaks. The free t-RNA of the P-site slips away and the A site carries peptidyl tRNA complex.
  4. Now the ribosome or mRNA rotates slightly. The process is called translocation.
  5. As a result of translocation, the A site codon along with peptidyl-tRNA complex reaches the P site. A new codon is exposed at the A site. It attracts a new amino-acyl tRNA complex.
  6. The process of bond formation and translocation is repeated. One by one all the codons of mRNA are exposed at the A' site and get decoded through incorporation of amino acids in the peptide chain. The peptide chain elongates.

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