![]() This allows RNA polymerase to bind to the promoter and freely transcribe the three genes, allowing the organism to metabolize the lactose.Įukaryotic cells, in contrast, have intracellular organelles and are much more complex. When lactose is present, an end product of lactose metabolism binds to the repressor protein and prevents it from binding to the operator. Thus very little of the protein products of the three genes is made. When there is no lactose present, a protein known as a repressor binds to the operator and prevents RNA polymerase from binding to the promoter, except in rare cases. The operon also contains a promoter sequence to which the RNA polymerase binds to begin transcription between the promoter and the three genes is a region called the operator. When lactose is present, the genes are transcribed and the bacterium is able to use the lactose as a food source. When lactose is not present in the bacterium’s environment, the lac genes are transcribed in small amounts. ![]() The lac operon is a stretch of DNA with three adjacent genes that code for proteins that participate in the absorption and metabolism of lactose, a food source for E. coli in the 1950s and 1960s by French researchers and is called the lac operon. The first example of such control was discovered using E. Therefore, in prokaryotic cells, the control of gene expression is almost entirely at the transcriptional level. When more protein is required, more transcription occurs. All the subsequent steps happen automatically. As a result, the primary method to control what type and how much protein is expressed in a prokaryotic cell is through the regulation of DNA transcription into RNA. When the protein is no longer needed, transcription stops. The process occurs in both prokaryotic and eukaryotic cells, just in slightly different fashions.īecause prokaryotic organisms lack a cell nucleus, the processes of transcription and translation occur almost simultaneously. To understand how gene expression is regulated, we must first understand how a gene becomes 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. Unicellular organisms, both eukaryotic and prokaryotic, also turn on and off genes in response to the demands of their environment so that they can respond to special conditions. In addition, cells will turn on or off certain genes at different times in response to changes in the environment or at different times during the development of the organism. Each cell also has many genes that are not expressed, and expresses many that are not expressed by other cells, such that it can carry out its specialized functions. All cells have certain basic functions they must perform for themselves, such as converting the energy in sugar molecules into energy in ATP. These differences are a consequence of the expression of different sets of genes in each of these cells. For example, a muscle cell is very different from a liver cell, which is very different from a skin cell. ![]() For this to occur, there must be a mechanism to 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.Ĭells in multicellular organisms are specialized cells in different tissues look very different and perform different functions. Whether in a simple unicellular organism or in a complex multicellular 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 organisms and cells control or regulate the transcription and translation of their DNA into protein. Understand that eukaryotic gene expression occurs at the epigenetic, transcriptional, post-transcriptional, translational, and post-translational levelsįor a cell to function properly, necessary proteins must be synthesized at the proper time.Describe how prokaryotic gene expression occurs at the transcriptional level.Discuss why every cell does not express all of its genes.Learning Objectives By the end of this section, you will be able to:
0 Comments
Leave a Reply. |