The α chain of eukaryotic hemoglobin is composed of 141 amino acids. What is the minimum number of nucleotides in an mRNA coding for this polypeptide chain?

Verified step by step guidance

1. Understand that each amino acid in a polypeptide chain is encoded by a sequence of three nucleotides in mRNA, called a codon.
2. Identify the total number of amino acids in the α chain, which is given as 141 amino acids.
3. Calculate the number of nucleotides needed to code for these amino acids by multiplying the number of amino acids by 3, since each amino acid corresponds to 3 nucleotides: $\mathrm{nucleotides}=\; 141\; imes\; 3$.
4. Remember to consider the stop codon, which signals the end of translation but does not code for an amino acid. The stop codon also consists of 3 nucleotides and must be included in the total nucleotide count.
5. Add the 3 nucleotides of the stop codon to the previous total to find the minimum number of nucleotides in the mRNA: $\mathrm{total\; nucleotides}=\; (141\; imes\; 3)\; +\; 3$.

Key Concepts

Genetic Code and Codons

The genetic code consists of nucleotide triplets called codons, each specifying a single amino acid. Since each amino acid is encoded by a sequence of three nucleotides, the length of the mRNA coding region depends on the number of amino acids in the protein.

mRNA Structure and Translation

mRNA carries the genetic information from DNA to the ribosome for protein synthesis. The coding region of mRNA includes codons for amino acids and a stop codon that signals termination of translation, which is essential for determining the total nucleotide count.

Stop Codon and Its Role

A stop codon (UAA, UAG, or UGA) signals the end of translation and does not code for an amino acid. Therefore, the mRNA must include an additional three nucleotides beyond those coding for amino acids to properly terminate protein synthesis.