Gene expression

Gene expression is how a gene's DNA sequence is turned into something the cell can use. For protein-coding genes it has two main steps: transcription copies the gene into messenger RNA, and translation uses that RNA to build a protein. Some genes stop at the RNA stage, making functional RNAs, such as ribosomal and transfer RNA, that never become protein.

Almost every cell in the body carries the same genome, so what makes a liver cell different from a neuron is which genes are switched on, and how strongly. Cells control expression at many points. Bacteria regulate mainly at transcription, often through operons. Eukaryotes can also act through chromatin packing and epigenetic marks, RNA processing and export, the rate of translation and changes to the finished protein, as well as how quickly RNAs and proteins are broken down. Tight control saves energy and lets cells respond to signals and their surroundings.

Researchers measure expression by counting RNA molecules, for example with RNA sequencing, or by detecting the protein itself. Faulty regulation contributes to many diseases, including cancer.