Chapter 17, Problem 17.77CQ

Interpretation Introduction

To determine: The number of nucleotides that are present in the mRNA, such that a polypeptide oxytocin containing 9 amino acids is formed.

Answer to Problem 17.77CQ

Solution:

A peptide chain of 9 amino acids have amino acids linked to each other. Each amino acid is encoded by a triplet of nucleotide known as codon.

For initiating the protein formation, a start codon is required and for termination, a stop codon is required.

For 9 amino acids: $\text{9×3 + 3 }\left(\text{start codon}\right)\text{ + 3 }\left(\text{stop codon}\right)\text{ = 33 nucleotides}$ .

Explanation of Solution

For initiation of protein synthesis, a start codon (AUG) is required so that the first amino acid is methionine. After that tRNA comes with amino acid and base pairs with mRNA to form a polypeptide chain. For the termination of peptide chain, stop codon (UAA, UAG and UGA) is required to stop the peptide formation or translation.

Each amino acid is coded by 3 bases due to which 9 amino acids are coded by 27 bases and for a peptide chain again 3 bases are required which are start codon (AUG) and for terminating the chain, a stop codon is also required and 3 bases are required for that as well. So, total of 33 nucleotide bases are required.

Conclusion

Hence, for 9 amino acids: $\text{9×3 + 3 }\left(\text{start codon}\right)\text{ + 3 }\left(\text{stop codon}\right)\text{ = 33 nucleotides}$ .