The blueprint of life is written in DNA, but almost all life processes are executed by proteins. To convert the information coded in the DNA into the wide array of proteins in each cell, segments of DNA sequence in the genome must be copied into messenger RNAs (mRNAs) first. The transcribed nucleotide sequences in the mRNAs are then translated into proteins through an information decoding process carried out by ribosomes. Because of the intermediary role played by mRNAs between DNA and proteins, the composition of mRNAs in a cell or population of cells-the transcriptome —is often used to study cellular processes and functions. Unlike the genome, which is mostly static and the same for every cell in an organism, the transcriptome is dynamically regulated and therefore can be used as a proxy of cellular functional status.