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Regulation of Gene Expression

Most of your somatic cells (from your head to your toes) have exactly the same genetic information in their nuclei. Yet it is obvious that these different cell types have very diverse structures and functions. This diversity arises because individual cells can regulate the expression of particular genes, turning them on, off, up and down as needed. This regulation can happen at the DNA, RNA or protein level, but we will focus on one mechanism for transcriptional regulation as an example.

In the anatomy of a gene section, we learned that genes often have regulatory sequences that determine if and when they get expressed. Most such regulatory sequences control gene expression by binding to specific proteins that either enhance or repress transcription.

This animation begins in a tissue in which a particular gene product is not needed. In this tissue, a repressor protein binds to a regulatory sequence, literally blocking the gene so that RNA polymerase cannot bind. Thus, gene expression is turned off. If this tissue needs to express the gene, either the repressor protein's production can be stopped or a second molecule, called an inducer, can be produced (or provided by the environment). The inducer will bind to the repressor and inactivate it, allowing transcription to occur.