It was surprisingly discovered in 1877 that the DNA is longer than the mRNA. But they should be the same length since mRNA is a direct copy of the DNA. This is due to the fact that immediately after the mRNA copy is made, sections are cut out before translation takes place.

              The section of the genes that code for the unused pieces of mRNA are called introns and the remaining section of the genes are those that code for proteins and are called exons.

            The size and the arrangement of introns are variable and the characteristic for particular gene. The existence of introns make the gene to code for several different, yet similar proteins increasing its potential use, an example is the calcitonian gene ending on which sections of the mRNA are removed. One is produce in the thyroid gland and code for the protein, calcitonine with 3e amino acid acting to lower the calcium level in blood, the order is produce in the hypothalamus and code for a protein with 37 amino acids called CGRP (calcitonin gene related peptide). This is a powerful vasodilating agent.