Question

Study the mRNA segment given below which is ready and complete to be translated into a polypeptide chain.

1. Write codons 'a' and 'b'.
2. What do they code for?
3. How is peptide bond formed between two amino acids in the ribosome?

Answer 1

1. Codon a is the initiation codon AUG; codon b is a termination codon—UAA, UAG or UGA (the exact stop codon depends on the sequence shown in the image). 
2. AUG codes for methionine; a stop codon codes for no amino acid and signals termination. 
3. Peptidyl transferase catalyses a peptide bond between the amino group of one amino acid and the carboxyl group of another, releasing water.