Genes operate by determining the kinds of proteins that are made by cells.
However DNA does not generate proteins directly. Rather DNA produces another polynucleotide RNA, which serves as a blueprint for protein synthesis. The length of mRNA depends on the size of protein or group of proteins that are to be synthesized. RNA like DNA is a long unbranched macromolecule consisting of nucleotides joined by 3'- 5' phosphodiester bonds. The number of nucleotides in RNA varies from 75 - to thousands.