Answer:
Gene regulation is the process of controlling which genes in a cell's DNA are expressed (used to make a functional product such as a protein).
Different cells in a multicellular organism may express very different sets of genes, even though they contain the same DNA.
The set of genes expressed in a cell determines the set of proteins and functional RNAs it contains, giving it its unique properties.
In eukaryotes like humans, gene expression involves many steps, and gene regulation can occur at any of these steps. However, many genes are regulated primarily at the level of transcription.
Introduction
Your amazing body contains hundreds of different cell types, from immune cells to skin cells to neurons. Almost all of your cells contain the same set of DNA instructions – so why do they look so different, and do such different jobs? The answer: different gene regulation!
Gene regulation makes cells different
Gene regulation is how a cell controls which genes, out of the many genes in its genome, are "turned on" (expressed). Thanks to gene regulation, each cell type in your body has a different set of active genes – despite the fact that almost all the cells of your body contain the exact same DNA. These different patterns of gene expression cause your various cell types to have different sets of proteins, making each cell type uniquely specialized to do its job.
For example, one of the jobs of the liver is to remove toxic substances like alcohol from the bloodstream. To do this, liver cells express genes encoding subunits (pieces) of an enzyme called alcohol dehydrogenase. This enzyme breaks alcohol down into a non-toxic molecule. The neurons in a person's brain don’t remove toxins from the body, so they keep these genes unexpressed, or “turned off.” Similarly, the cells of the liver don’t send signals using neurotransmitters, so they keep neurotransmitter genes turned off.
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