Operons are groups of genes controlled by a single promoter, found only in simple organisms like bacteria. They can be induced or repressed by activators or inhibitors, and some rely on effectors. Operons are an efficient evolutionary motif with different functions, such as managing amino acid production and sugar metabolism.
An operon is a group of genes that is read together as a single unit. Operons are usually under the control of a single region of the gene that directs reading, called the promoter. Depending on the organism, one or more proteins assemble at the promoter to stimulate the reading of genes. Genes are often read, or transcribed, as one long transcript, but this is not always the case. Only simple organisms, like bacteria, contain operons, and those genes are each long stretches of DNA specialized for a particular task.
The control of an operon is tightly regulated in bacteria. Just as there are proteins that activate operons, there are proteins that can deactivate operons. When turned on, operons are said to be induced, and when turned off, they are said to be repressed. In general, interacting with proteins activates them and dissociation from proteins deactivates them, but the reverse can also be true, depending on the operons.
Proteins that activate an operon are called activators, while those that deactivate operons are called inhibitors. At any moment, both activators and inhibitors are available in the cell. Most activators and inhibitors work by stimulating or blocking the promoter. Some operons are under more complex control than this, also relying on activators or inhibitors that interact with DNA away from them. These distant molecules are often called effectors or allosteric molecules.
The combination of simple structure and tight control caused operons to spread among bacteria. An operon is an evolutionary efficient motif that works in a variety of environments. While the immediate environment of operons can sometimes impact their productivity, particularly if the temperature or pH in a cell is not at an optimal level, their general structure always remains the same. Genes within operons are never uncoupled from each other and regardless of the stress on a cell, they are always transcribed together and in their entirety.
A variety of operons are well characterized in many species of bacteria and have different functions among different organisms. There are operons that manage the production of amino acids, which are the building blocks of proteins, and operons that manage the metabolism of sugars. They are extremely versatile genetic elements, allowing genes that do significantly different things to work together in concert.
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