Study the mRNA segment given above which is complete to be translated into a polypeptide chain.
(i) Write the codons 'a' and 'b'.
(ii) What do they code for?
(iii) How is peptide bond formed between two amino acids in the ribosome?
(i) 'a' is AUG
'b' is UAG| UGA| UAG
(ii) AUG codes for methionine whereas UAG| UGA| UGA are stop codon. They do not code for any amino acids. They terminate the process of protein synthesis.
(iii) There are two sites in the large subunit. when two charged tRNA bind to these sites, peptide bond is formed. The activation of amino acid by ATP provides energy for the formation of peptide. The ribosome acts as a catalyst (23S rRNA in bacteria is the enzyme-ribozyme) for the formation of peptide bond.