Gene expression is the process by which the information encoded in a gene is turned into a function. This mostly occurs via the transcription of RNA molecules that code for proteins or non-coding RNA molecules that serve other functions. Gene expression be thought of as an “on/off switch” to control when and where RNA molecules and proteins are made and as a “volume control” to determine how much of those products are made. The process of gene expression is carefully regulated, changing substantially under different conditions and cell types. The RNA and protein products of many genes serve to regulate the expression of other genes. Where, when, and how much a gene is expressed can also assessed by measuring the functional activity of a gene product or observing a phenotype associated with a gene.

With current technologies, we have the ability to measure mRNA expression of every gene in the entire genome. Sometimes, we can do that in individual cells. This is a really powerful tool to help us measure which genes are turned on, how much and where. Classically, we can also measure gene expression by observing a phenotype or a trait. Examples of those would be to measure a protein activity. If a protein activity can be measured, the gene that encodes for that protein is probably turned on or we can define it as turned on. We can also look for patterns and traits. So for example, if a beautiful butterfly wing with multiple colors is the result of different genes being turned on in different places in the butterfly wing, then we can measure that gene expression simply by observing the wing of the butterfly and marking the locations of the colors.

Lawrence Brody, Ph.D., Director, Division of Genomics and Society

Most genes contain the information needed to make functional molecules called proteins. (A few genes produce regulatory molecules that help the cell assemble proteins.) The journey from gene to protein is complex and tightly controlled within each cell. It consists of two major steps: transcription and translation. Together, transcription and translation are known as gene expression.

During the process of transcription, the information stored in a gene's DNA is passed to a similar molecule called RNA (ribonucleic acid) in the cell nucleus. Both RNA and DNA are made up of a chain of building blocks called nucleotides, but they have slightly different chemical properties. The type of RNA that contains the information for making a protein is called messenger RNA (mRNA) because it carries the information, or message, from the DNA out of the nucleus into the cytoplasm.

Translation, the second step in getting from a gene to a protein, takes place in the cytoplasm. The mRNA interacts with a specialized complex called a ribosome, which "reads" the sequence of mRNA nucleotides. Each sequence of three nucleotides, called a codon, usually codes for one particular amino acid. (Amino acids are the building blocks of proteins.) A type of RNA called transfer RNA (tRNA) assembles the protein, one amino acid at a time. Protein assembly continues until the ribosome encounters a “stop” codon (a sequence of three nucleotides that does not code for an amino acid).

The flow of information from DNA to RNA to proteins is one of the fundamental principles of molecular biology. It is so important that it is sometimes called the “central dogma.”

Transcription is the process of making an RNA copy of a gene sequence. This copy, called a messenger RNA (mRNA) molecule, leaves the cell nucleus and enters the cytoplasm, where it directs the synthesis of the protein, which it encodes.

Transcription is one of the fundamental processes that happens to our genome. It's the process of turning DNA into RNA. And you may have heard about the central dogma, which is DNA, to RNA, to protein. Well, transcription refers to that first part of going from DNA to RNA. And we transcribe DNA to RNA in specific places. The most popular places are those things that code for these protein-encoding genes. But there are a whole host of other RNAs that get transcribed, like transfer RNAs and ribosomal RNAs, that do other functions that are genomic as well.

Translation, as related to genomics, is the process through which information encoded in messenger RNA (mRNA) directs the addition of amino acids during protein synthesis. Translation takes place on ribosomes in the cell cytoplasm, where mRNA is read and translated into the string of amino acid chains that make up the synthesized protein.

Translation. Translation is, perhaps, the single most important event in biology because what protein is translated versus what isn't translated makes the difference between your body building a heart versus lungs.

Prabarna Ganguly, Ph.D., Chief Communications Officer, Nucleus Genomics

Each cell expresses, or turns on, only a fraction of its genes. The rest of the genes are repressed, or turned off. The process of turning genes on and off is known as gene regulation. Gene regulation is an important part of normal development. Genes are turned on and off in different patterns during development to make a brain cell look and act different from a liver cell or a muscle cell, for example. Gene regulation also allows cells to react quickly to changes in their environments. Although we know that the regulation of genes is critical for life, this complex process is not yet fully understood.

Gene regulation can occur at any point during gene expression, but most commonly occurs at the level of transcription (when the information in a gene’s DNA is transferred to mRNA). Signals from the environment or from other cells activate proteins called transcription factors. These proteins bind to regulatory regions of a gene and increase or decrease the level of transcription. By controlling the level of transcription, this process can determine the amount of protein product that is made by a gene at any given time.