![]() When the resulting protein is no longer needed, transcription stops. To synthesize a protein, the processes of transcription and translation occur almost simultaneously. Prokaryotic organisms are single-celled organisms that lack a cell nucleus, and their DNA therefore floats freely in the cell cytoplasm. The process occurs in both prokaryotic and eukaryotic cells, just in slightly different manners. To understand how gene expression is regulated, we must first understand how a gene codes for a functional protein in a cell. Prokaryotic versus Eukaryotic Gene Expression Malfunctions in this process are detrimental to the cell and can lead to the development of many diseases, including cancer. The control of gene expression is extremely complex. Cells would have to be enormous if every protein were expressed in every cell all the time. In addition, only expressing a subset of genes in each cell saves space because DNA must be unwound from its tightly coiled structure to transcribe and translate the DNA. It would require a significant amount of energy for an organism to express every gene at all times, so it is more energy efficient to turn on the genes only when they are required. The regulation of gene expression conserves energy and space. For this to occur, there must be internal chemical mechanisms that control when a gene is expressed to make RNA and protein, how much of the protein is made, and when it is time to stop making that protein because it is no longer needed. Whether in a simple unicellular organism or a complex multi-cellular organism, each cell controls when and how its genes are expressed. ![]() The process of turning on a gene to produce RNA and protein is called gene expression. All cells control or regulate the synthesis of proteins from information encoded in their DNA. For a cell to function properly, necessary proteins must be synthesized at the proper time and place.
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