What is the estimated nucleotide composition of the mRNA that encodes the protein from which ghrelin is cleaved?

• A. More than 28 amino acids
• B. Exactly 84 nucleotides
• C. Exactly 87 nucleotides
• D. More than 87 nucleotides

Answer: (D)

The correct choice is based on the understanding of how proteins are translated from mRNA. Each amino acid is encoded by a sequence of three nucleotides, known as a codon, in mRNA. When assessing the mRNA that encodes a protein, we need to consider not only the length of the protein in terms of the number of amino acids but also the additional nucleotides required for regulatory elements and the machinery of translation, such as start and stop codons.

Ghrelin is a peptide hormone that is derived from a larger precursor protein called preproghrelin. The mature ghrelin peptide consists of 28 amino acids. To calculate the minimum nucleotide length of mRNA needed to encode this, one would multiply the number of amino acids by three (since each amino acid is represented by three nucleotides) to find the minimum required, which gives us 28 × 3 = 84 nucleotides.

However, this calculation does not account for additional nucleotides which include the start codon (AUG), stop codons, and potentially untranslated regions (UTRs) both at the 5' and 3' ends of the mRNA. Therefore, the actual length of the mRNA is