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What do genes do?

Genes tell a cell how to make proteins. Roughly speaking, each gene is a set of instructions for making one specific protein.

Bross, P. et al. Protein misfolding and degradation in genetic diseases. Hum Mutat 14, 186-198 (1999).

Proteins are a diverse group of large, complex molecules that are crucial to every aspect of the body's structure and function. Collagen, which forms the structural scaffolding of skin and many other tissues, is a protein. Insulin, a hormone that regulates blood sugar, is a protein. Trypsin, an enzyme involved in digestion, is a protein. So is the pigment melanin, which gives hair and skin its color. Still other proteins regulate the body's production of proteins.

Genes sometimes affect characteristics in indirect ways. For example, genes affect the size and shape of your nose, even though there's no such thing as a "nose size" protein. But directly or indirectly, the way genes influence your traits is by telling your cells which proteins to make, how much, when, and where.

What do genes look like?

A gene has several parts. In most genes, the protein-making instructions are broken up into relatively short sections called exons. These are interspersed with introns, longer sections of "extra" or "nonsense" DNA. Genes also contain regulatory sequences, which help determine where, when, and in what amount proteins are made.

Though still poorly understood, these regulatory sequences are crucial to how your body works. They help determine which genes are "turned on," or transmitting their protein-making instructions to the rest of the cell, in different cells throughout the body. All your cells contain the same genes, but cells don't make all the proteins they have genes for. Thus, what makes a liver cell different from a brain cell is which proteins it makes—and therefore, which of its genes are turned on.

A schematic drawing of a gene including these features looks like a ribbon divided into segments. But like many schematic drawings, this one is quite different from the physical reality of a gene. Actually, a gene is rather nondescript from a physical point of view. It basically looks like any other piece of DNA.

As far as we know right now, genes offer few clues to the human observer about where they begin and end, and where an intron and an exon meet—which is just one of the many challenges scientists face in finding and studying genes.

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