Final answer:
The correct composition of the mRNA encoding a 28 amino acid peptide like ghrelin would be more than 87 nucleotides, as it requires 84 nucleotides for the amino acids themselves plus additional nucleotides for the start and stop codons.
Step-by-step explanation:
The composition of the mRNA that encodes for a protein from which ghrelin is cleaved can be determined by understanding the relationship between nucleotides and amino acids in the process of protein synthesis known as translation.
Since each amino acid is defined by a triplet of nucleotides known as a codon, and the peptide in question consists of 28 amino acids, we can calculate the number of nucleotides needed to encode those amino acids.
For a 28 amino acid peptide, a minimum of 28 codons are needed, with each codon consisting of 3 nucleotides. Hence, 28 amino acids multiplied by 3 nucleotides per amino acid equals 84 nucleotides.
However, this calculation does not include the start and stop codons which are also part of the mRNA. The start codon AUG is necessary for the initiation of translation, and there is typically a single stop codon signaling the end of translation.
Therefore, the correct mRNA length would be more than 84 nucleotides due to the start codon and more than 87 nucleotides if the stop codon is also included.