{"id":3289,"date":"2016-11-17T00:17:06","date_gmt":"2016-11-17T00:17:06","guid":{"rendered":"https:\/\/courses.lumenlearning.com\/wm-biology1\/?post_type=chapter&#038;p=3289"},"modified":"2024-04-29T16:30:50","modified_gmt":"2024-04-29T16:30:50","slug":"reading-activators-and-inducers","status":"publish","type":"chapter","link":"https:\/\/courses.lumenlearning.com\/wm-biology1\/chapter\/reading-activators-and-inducers\/","title":{"raw":"Activators and Inducers","rendered":"Activators and Inducers"},"content":{"raw":"<div class=\"textbox learning-objectives\">\r\n<h3>Learning Outcomes<\/h3>\r\n<ul>\r\n \t<li>Explain the role of activators and inducers in positive gene regulation<\/li>\r\n<\/ul>\r\n<\/div>\r\n<h2>Catabolite Activator Protein (CAP): An Activator Regulator<\/h2>\r\n<p id=\"fs-idm148740496\">Just as the <em>trp<\/em> operon is negatively regulated by tryptophan molecules, there are proteins that bind to the operator sequences that act as a <strong>positive regulator<\/strong> to turn genes on and activate them. For example, when glucose is scarce, <em>E. coli<\/em> bacteria can turn to other sugar sources for fuel. To do this, new genes to process these alternate sugars must be transcribed. When glucose levels drop, cyclic AMP (cAMP) begins to accumulate in the cell. The cAMP molecule is a signaling molecule that is involved in glucose and energy metabolism in <em>E. coli<\/em>. When glucose levels decline in the cell, accumulating cAMP binds to the positive regulator <strong>catabolite activator protein (CAP)<\/strong>, a protein that binds to the promoters of operons that control the processing of alternative sugars. When cAMP binds to CAP, the complex binds to the promoter region of the genes that are needed to use the alternate sugar sources (Figure 1). In these operons, a CAP binding site is located upstream of the RNA polymerase binding site in the promoter. This increases the binding ability of RNA polymerase to the promoter region and the transcription of the genes.<\/p>\r\n\r\n\r\n[caption id=\"attachment_3558\" align=\"aligncenter\" width=\"800\"]<img class=\"wp-image-3558 size-full\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/1087\/2016\/11\/17162207\/Figure_16_02_02.jpg\" alt=\"The lac operon consists of a promoter, an operator, and three genes named lacZ, lacY, and lacA that are located in sequential order on the DNA. In the absence of cAMP, the CAP protein does not bind the DNA. RNA polymerase binds the promoter, and transcription occurs at a slow rate. In the presence of cAMP, a CAP\u2013cAMP complex binds to the promoter and increases RNA polymerase activity. As a result, the rate of RNA synthesis is increased.\" width=\"800\" height=\"474\" \/> Figure 1. When glucose levels fall, <em>E. coli<\/em> may use other sugars for fuel but must transcribe new genes to do so. As glucose supplies become limited, cAMP levels increase. This cAMP binds to the CAP protein, a positive regulator that binds to an operator region upstream of the genes required to use other sugar sources.[\/caption]\r\n<h2>Lactose Operon: An Inducer Operon<\/h2>\r\n<p id=\"fs-idm17029296\">The third type of gene regulation in prokaryotic cells occurs through\u00a0<em data-effect=\"italics\">inducible operons<\/em>, which have proteins that bind to activate or repress transcription depending on the local environment and the needs of the cell. The\u00a0<em data-effect=\"italics\">lac<\/em>\u00a0operon is a typical inducible operon. As mentioned previously,\u00a0<em data-effect=\"italics\">E. coli<\/em>\u00a0is able to use other sugars as energy sources when glucose concentrations are low. One such sugar source is lactose. The<strong>\u00a0<span id=\"term601\" data-type=\"term\"><em data-effect=\"italics\">lac<\/em>\u00a0operon<\/span><\/strong>\u00a0encodes the genes necessary to acquire and process the lactose from the local environment. The Z gene of the\u00a0<em data-effect=\"italics\">lac<\/em>\u00a0operon encodes beta-galactosidase, which breaks lactose down to glucose and galactose.<\/p>\r\n<p id=\"fs-idm17030296\">However, for the\u00a0<em data-effect=\"italics\">lac<\/em>\u00a0operon to be activated, two conditions must be met. First, the level of glucose must be very low or non-existent. Second, lactose must be present. Only when glucose is absent and lactose is present will the\u00a0<em data-effect=\"italics\">lac<\/em>\u00a0operon be transcribed (Figure 2). In the absence of glucose, the binding of the CAP protein makes transcription of the\u00a0<em data-effect=\"italics\">lac<\/em>\u00a0operon more effective. When lactose is present, its metabolite, allolactose, binds to the\u00a0<em data-effect=\"italics\">lac<\/em>\u00a0repressor and changes its shape so that it cannot bind to the\u00a0<em data-effect=\"italics\">lac<\/em>\u00a0operator to prevent transcription. This combination of conditions makes sense for the cell, because it would be energetically wasteful to synthesize the enzymes to process lactose if glucose was plentiful or lactose was not available. It should be mentioned that the lac operon is transcribed at a very low rate even when glucose is present and lactose absent.<\/p>\r\n\r\n<div class=\"textbox exercises\">\r\n<h3>Practice Question<\/h3>\r\nTranscription of the <em>lac<\/em> operon is carefully regulated so that its expression only occurs when glucose is limited and lactose is present to serve as an alternative fuel source.\r\n\r\n[caption id=\"attachment_3560\" align=\"aligncenter\" width=\"469\"]<img class=\"wp-image-3560 size-full\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/1087\/2016\/11\/17162744\/Figure_16_02_03.png\" alt=\"The lac operon consists of a promoter, an operator, and three genes named lacZ, lacY, and lacA. RNA polymerase binds to the promoter. In the absence of lactose, the lac repressor binds to the operator and prevents RNA polymerase from transcribing the operon. In the presence of lactose, the repressor is released from the operator, and transcription proceeds at a slow rate. Binding of the cAMP\u2013CAP complex to the promoter stimulates RNA polymerase activity and increases RNA synthesis. However, even in the presence of the cAMP\u2013CAP complex, RNA synthesis is blocked if the repressor binds to the promoter.\" width=\"469\" height=\"829\" \/> Figure 2. Regulation of the lac operon.[\/caption]\r\n\r\n&nbsp;\r\n\r\nIn <em>E. coli<\/em>, the <em>trp<\/em> operon is on by default, while the <em>lac<\/em> operon is off. Why do you think this is the case?\r\n\r\n[practice-area rows=\"2\"][\/practice-area]\r\n[reveal-answer q=\"703127\"]Show Answer[\/reveal-answer]\r\n[hidden-answer a=\"703127\"]Tryptophan is an amino acid essential for making proteins, so the cell always needs to have some on hand. However, if plenty of tryptophan is present, it is wasteful to make more, and the expression of the <em>trp<\/em> receptor is repressed. Lactose, a sugar found in milk, is not always available. It makes no sense to make the enzymes necessary to digest an energy source that is not available, so the lac operon is only turned on when lactose is present.[\/hidden-answer]\r\n\r\n<\/div>\r\nIf glucose is absent, then CAP can bind to the operator sequence to activate transcription. If lactose is absent, then the repressor binds to the operator to prevent transcription. If either of these requirements is met, then transcription remains off. Only when both conditions are satisfied is the <em>lac<\/em> operon transcribed (Table 1).\r\n<table id=\"tab-ch16_02_01\" summary=\"\">\r\n<thead>\r\n<tr>\r\n<th colspan=\"5\" scope=\"col\" data-align=\"left\">Table 1. Signals that Induce or Repress Transcription of the <em>lac<\/em> Operon<\/th>\r\n<\/tr>\r\n<tr>\r\n<th scope=\"col\" data-align=\"center\">Glucose<\/th>\r\n<th scope=\"col\" data-align=\"center\">CAP binds<\/th>\r\n<th scope=\"col\" data-align=\"center\">Lactose<\/th>\r\n<th scope=\"col\" data-align=\"center\">Repressor binds<\/th>\r\n<th scope=\"col\" data-align=\"center\">Transcription<\/th>\r\n<\/tr>\r\n<\/thead>\r\n<tbody>\r\n<tr>\r\n<td data-align=\"center\">+<\/td>\r\n<td data-align=\"center\">\u2212<\/td>\r\n<td data-align=\"center\">\u2212<\/td>\r\n<td data-align=\"center\">+<\/td>\r\n<td data-align=\"center\">No<\/td>\r\n<\/tr>\r\n<tr>\r\n<td data-align=\"center\">+<\/td>\r\n<td data-align=\"center\">\u2212<\/td>\r\n<td data-align=\"center\">+<\/td>\r\n<td data-align=\"center\">\u2212<\/td>\r\n<td data-align=\"center\">Some<\/td>\r\n<\/tr>\r\n<tr>\r\n<td data-align=\"center\">\u2212<\/td>\r\n<td data-align=\"center\">+<\/td>\r\n<td data-align=\"center\">\u2212<\/td>\r\n<td data-align=\"center\">+<\/td>\r\n<td data-align=\"center\">No<\/td>\r\n<\/tr>\r\n<tr>\r\n<td data-align=\"center\">\u2212<\/td>\r\n<td data-align=\"center\">+<\/td>\r\n<td data-align=\"center\">+<\/td>\r\n<td data-align=\"center\">\u2212<\/td>\r\n<td data-align=\"center\">Yes<\/td>\r\n<\/tr>\r\n<\/tbody>\r\n<\/table>\r\n<div class=\"textbox shaded\">\r\n\r\nWatch an animated tutorial about the workings of <em>lac<\/em> operon here.\r\n\r\n<iframe src=\"\/\/plugin.3playmedia.com\/show?ad=1&amp;ad_autoplay=0&amp;ad_default_source_volume_control=0&amp;ad_source_volume_control=0&amp;mf=4409383&amp;p3sdk_version=1.10.1&amp;p=20361&amp;pt=573&amp;video_id=iPQZXMKZEfw&amp;video_target=tpm-plugin-63e765tk-iPQZXMKZEfw\" width=\"800px\" height=\"500px\" frameborder=\"0\" marginwidth=\"0px\" marginheight=\"0px\"><\/iframe>\r\n\r\nYou can <a href=\"https:\/\/oerfiles.s3-us-west-2.amazonaws.com\/WM-BiologyforMajors\/Transcripts\/OperonLAC_Transcription.txt\" target=\"_blank\" rel=\"noopener\">view the transcript for \"Operon LAC\" here (link opens in new window).<\/a>\r\n\r\n<\/div>\r\n<div class=\"textbox exercises\">\r\n<h3>Practice Questions<\/h3>\r\nIf glucose is absent, but so is lactose, the lac operon will be ________.\r\n<ol>\r\n \t<li>activated<\/li>\r\n \t<li>repressed<\/li>\r\n \t<li>activated, but only partially<\/li>\r\n \t<li>mutated<\/li>\r\n<\/ol>\r\n[reveal-answer q=\"88859\"]Show Answer[\/reveal-answer]\r\n[hidden-answer a=\"88859\"]Answer b. If glucose is absent, but so is lactose, the lac operon will be repressed.\r\n\r\n[\/hidden-answer]\r\n\r\nDescribe how transcription in prokaryotic cells can be altered by external stimulation such as excess lactose in the environment.\r\n\r\n[practice-area rows=\"2\"][\/practice-area]\r\n[reveal-answer q=\"742266\"]Show Answer[\/reveal-answer]\r\n[hidden-answer a=\"742266\"]Environmental stimuli can increase or induce transcription in prokaryotic cells. In this example, lactose in the environment will induce the transcription of the <em>lac<\/em> operon, but only if glucose is not available in the environment.\r\n\r\n[\/hidden-answer]\r\n\r\nWhat is the difference between a repressible and an inducible operon?\r\n\r\n[practice-area rows=\"2\"][\/practice-area]\r\n[reveal-answer q=\"353005\"]Show Answer[\/reveal-answer]\r\n[hidden-answer a=\"353005\"]A repressible operon uses a protein bound to the promoter region of a gene to keep the gene repressed or silent. This repressor must be actively removed in order to transcribe the gene. An inducible operon is either activated or repressed depending on the needs of the cell and what is available in the local environment.[\/hidden-answer]\r\n\r\n<\/div>\r\n<div class=\"textbox tryit\">\r\n<h3>Try It<\/h3>\r\nhttps:\/\/assess.lumenlearning.com\/practice\/de943158-b257-45d0-8c10-be0616485bf4\r\n<\/div>","rendered":"<div class=\"textbox learning-objectives\">\n<h3>Learning Outcomes<\/h3>\n<ul>\n<li>Explain the role of activators and inducers in positive gene regulation<\/li>\n<\/ul>\n<\/div>\n<h2>Catabolite Activator Protein (CAP): An Activator Regulator<\/h2>\n<p id=\"fs-idm148740496\">Just as the <em>trp<\/em> operon is negatively regulated by tryptophan molecules, there are proteins that bind to the operator sequences that act as a <strong>positive regulator<\/strong> to turn genes on and activate them. For example, when glucose is scarce, <em>E. coli<\/em> bacteria can turn to other sugar sources for fuel. To do this, new genes to process these alternate sugars must be transcribed. When glucose levels drop, cyclic AMP (cAMP) begins to accumulate in the cell. The cAMP molecule is a signaling molecule that is involved in glucose and energy metabolism in <em>E. coli<\/em>. When glucose levels decline in the cell, accumulating cAMP binds to the positive regulator <strong>catabolite activator protein (CAP)<\/strong>, a protein that binds to the promoters of operons that control the processing of alternative sugars. When cAMP binds to CAP, the complex binds to the promoter region of the genes that are needed to use the alternate sugar sources (Figure 1). In these operons, a CAP binding site is located upstream of the RNA polymerase binding site in the promoter. This increases the binding ability of RNA polymerase to the promoter region and the transcription of the genes.<\/p>\n<div id=\"attachment_3558\" style=\"width: 810px\" class=\"wp-caption aligncenter\"><img loading=\"lazy\" decoding=\"async\" aria-describedby=\"caption-attachment-3558\" class=\"wp-image-3558 size-full\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/1087\/2016\/11\/17162207\/Figure_16_02_02.jpg\" alt=\"The lac operon consists of a promoter, an operator, and three genes named lacZ, lacY, and lacA that are located in sequential order on the DNA. In the absence of cAMP, the CAP protein does not bind the DNA. RNA polymerase binds the promoter, and transcription occurs at a slow rate. In the presence of cAMP, a CAP\u2013cAMP complex binds to the promoter and increases RNA polymerase activity. As a result, the rate of RNA synthesis is increased.\" width=\"800\" height=\"474\" \/><\/p>\n<p id=\"caption-attachment-3558\" class=\"wp-caption-text\">Figure 1. When glucose levels fall, <em>E. coli<\/em> may use other sugars for fuel but must transcribe new genes to do so. As glucose supplies become limited, cAMP levels increase. This cAMP binds to the CAP protein, a positive regulator that binds to an operator region upstream of the genes required to use other sugar sources.<\/p>\n<\/div>\n<h2>Lactose Operon: An Inducer Operon<\/h2>\n<p id=\"fs-idm17029296\">The third type of gene regulation in prokaryotic cells occurs through\u00a0<em data-effect=\"italics\">inducible operons<\/em>, which have proteins that bind to activate or repress transcription depending on the local environment and the needs of the cell. The\u00a0<em data-effect=\"italics\">lac<\/em>\u00a0operon is a typical inducible operon. As mentioned previously,\u00a0<em data-effect=\"italics\">E. coli<\/em>\u00a0is able to use other sugars as energy sources when glucose concentrations are low. One such sugar source is lactose. The<strong>\u00a0<span id=\"term601\" data-type=\"term\"><em data-effect=\"italics\">lac<\/em>\u00a0operon<\/span><\/strong>\u00a0encodes the genes necessary to acquire and process the lactose from the local environment. The Z gene of the\u00a0<em data-effect=\"italics\">lac<\/em>\u00a0operon encodes beta-galactosidase, which breaks lactose down to glucose and galactose.<\/p>\n<p id=\"fs-idm17030296\">However, for the\u00a0<em data-effect=\"italics\">lac<\/em>\u00a0operon to be activated, two conditions must be met. First, the level of glucose must be very low or non-existent. Second, lactose must be present. Only when glucose is absent and lactose is present will the\u00a0<em data-effect=\"italics\">lac<\/em>\u00a0operon be transcribed (Figure 2). In the absence of glucose, the binding of the CAP protein makes transcription of the\u00a0<em data-effect=\"italics\">lac<\/em>\u00a0operon more effective. When lactose is present, its metabolite, allolactose, binds to the\u00a0<em data-effect=\"italics\">lac<\/em>\u00a0repressor and changes its shape so that it cannot bind to the\u00a0<em data-effect=\"italics\">lac<\/em>\u00a0operator to prevent transcription. This combination of conditions makes sense for the cell, because it would be energetically wasteful to synthesize the enzymes to process lactose if glucose was plentiful or lactose was not available. It should be mentioned that the lac operon is transcribed at a very low rate even when glucose is present and lactose absent.<\/p>\n<div class=\"textbox exercises\">\n<h3>Practice Question<\/h3>\n<p>Transcription of the <em>lac<\/em> operon is carefully regulated so that its expression only occurs when glucose is limited and lactose is present to serve as an alternative fuel source.<\/p>\n<div id=\"attachment_3560\" style=\"width: 479px\" class=\"wp-caption aligncenter\"><img loading=\"lazy\" decoding=\"async\" aria-describedby=\"caption-attachment-3560\" class=\"wp-image-3560 size-full\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/1087\/2016\/11\/17162744\/Figure_16_02_03.png\" alt=\"The lac operon consists of a promoter, an operator, and three genes named lacZ, lacY, and lacA. RNA polymerase binds to the promoter. In the absence of lactose, the lac repressor binds to the operator and prevents RNA polymerase from transcribing the operon. In the presence of lactose, the repressor is released from the operator, and transcription proceeds at a slow rate. Binding of the cAMP\u2013CAP complex to the promoter stimulates RNA polymerase activity and increases RNA synthesis. However, even in the presence of the cAMP\u2013CAP complex, RNA synthesis is blocked if the repressor binds to the promoter.\" width=\"469\" height=\"829\" \/><\/p>\n<p id=\"caption-attachment-3560\" class=\"wp-caption-text\">Figure 2. Regulation of the lac operon.<\/p>\n<\/div>\n<p>&nbsp;<\/p>\n<p>In <em>E. coli<\/em>, the <em>trp<\/em> operon is on by default, while the <em>lac<\/em> operon is off. Why do you think this is the case?<\/p>\n<p><textarea aria-label=\"Your Answer\" rows=\"2\"><\/textarea><\/p>\n<div class=\"qa-wrapper\" style=\"display: block\"><span class=\"show-answer collapsed\" style=\"cursor: pointer\" data-target=\"q703127\">Show Answer<\/span><\/p>\n<div id=\"q703127\" class=\"hidden-answer\" style=\"display: none\">Tryptophan is an amino acid essential for making proteins, so the cell always needs to have some on hand. However, if plenty of tryptophan is present, it is wasteful to make more, and the expression of the <em>trp<\/em> receptor is repressed. Lactose, a sugar found in milk, is not always available. It makes no sense to make the enzymes necessary to digest an energy source that is not available, so the lac operon is only turned on when lactose is present.<\/div>\n<\/div>\n<\/div>\n<p>If glucose is absent, then CAP can bind to the operator sequence to activate transcription. If lactose is absent, then the repressor binds to the operator to prevent transcription. If either of these requirements is met, then transcription remains off. Only when both conditions are satisfied is the <em>lac<\/em> operon transcribed (Table 1).<\/p>\n<table id=\"tab-ch16_02_01\" summary=\"\">\n<thead>\n<tr>\n<th colspan=\"5\" scope=\"col\" data-align=\"left\">Table 1. Signals that Induce or Repress Transcription of the <em>lac<\/em> Operon<\/th>\n<\/tr>\n<tr>\n<th scope=\"col\" data-align=\"center\">Glucose<\/th>\n<th scope=\"col\" data-align=\"center\">CAP binds<\/th>\n<th scope=\"col\" data-align=\"center\">Lactose<\/th>\n<th scope=\"col\" data-align=\"center\">Repressor binds<\/th>\n<th scope=\"col\" data-align=\"center\">Transcription<\/th>\n<\/tr>\n<\/thead>\n<tbody>\n<tr>\n<td data-align=\"center\">+<\/td>\n<td data-align=\"center\">\u2212<\/td>\n<td data-align=\"center\">\u2212<\/td>\n<td data-align=\"center\">+<\/td>\n<td data-align=\"center\">No<\/td>\n<\/tr>\n<tr>\n<td data-align=\"center\">+<\/td>\n<td data-align=\"center\">\u2212<\/td>\n<td data-align=\"center\">+<\/td>\n<td data-align=\"center\">\u2212<\/td>\n<td data-align=\"center\">Some<\/td>\n<\/tr>\n<tr>\n<td data-align=\"center\">\u2212<\/td>\n<td data-align=\"center\">+<\/td>\n<td data-align=\"center\">\u2212<\/td>\n<td data-align=\"center\">+<\/td>\n<td data-align=\"center\">No<\/td>\n<\/tr>\n<tr>\n<td data-align=\"center\">\u2212<\/td>\n<td data-align=\"center\">+<\/td>\n<td data-align=\"center\">+<\/td>\n<td data-align=\"center\">\u2212<\/td>\n<td data-align=\"center\">Yes<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<div class=\"textbox shaded\">\n<p>Watch an animated tutorial about the workings of <em>lac<\/em> operon here.<\/p>\n<p><iframe loading=\"lazy\" src=\"\/\/plugin.3playmedia.com\/show?ad=1&amp;ad_autoplay=0&amp;ad_default_source_volume_control=0&amp;ad_source_volume_control=0&amp;mf=4409383&amp;p3sdk_version=1.10.1&amp;p=20361&amp;pt=573&amp;video_id=iPQZXMKZEfw&amp;video_target=tpm-plugin-63e765tk-iPQZXMKZEfw\" width=\"800px\" height=\"500px\" frameborder=\"0\" marginwidth=\"0px\" marginheight=\"0px\"><\/iframe><\/p>\n<p>You can <a href=\"https:\/\/oerfiles.s3-us-west-2.amazonaws.com\/WM-BiologyforMajors\/Transcripts\/OperonLAC_Transcription.txt\" target=\"_blank\" rel=\"noopener\">view the transcript for &#8220;Operon LAC&#8221; here (link opens in new window).<\/a><\/p>\n<\/div>\n<div class=\"textbox exercises\">\n<h3>Practice Questions<\/h3>\n<p>If glucose is absent, but so is lactose, the lac operon will be ________.<\/p>\n<ol>\n<li>activated<\/li>\n<li>repressed<\/li>\n<li>activated, but only partially<\/li>\n<li>mutated<\/li>\n<\/ol>\n<div class=\"qa-wrapper\" style=\"display: block\"><span class=\"show-answer collapsed\" style=\"cursor: pointer\" data-target=\"q88859\">Show Answer<\/span><\/p>\n<div id=\"q88859\" class=\"hidden-answer\" style=\"display: none\">Answer b. If glucose is absent, but so is lactose, the lac operon will be repressed.<\/p>\n<\/div>\n<\/div>\n<p>Describe how transcription in prokaryotic cells can be altered by external stimulation such as excess lactose in the environment.<\/p>\n<p><textarea aria-label=\"Your Answer\" rows=\"2\"><\/textarea><\/p>\n<div class=\"qa-wrapper\" style=\"display: block\"><span class=\"show-answer collapsed\" style=\"cursor: pointer\" data-target=\"q742266\">Show Answer<\/span><\/p>\n<div id=\"q742266\" class=\"hidden-answer\" style=\"display: none\">Environmental stimuli can increase or induce transcription in prokaryotic cells. In this example, lactose in the environment will induce the transcription of the <em>lac<\/em> operon, but only if glucose is not available in the environment.<\/p>\n<\/div>\n<\/div>\n<p>What is the difference between a repressible and an inducible operon?<\/p>\n<p><textarea aria-label=\"Your Answer\" rows=\"2\"><\/textarea><\/p>\n<div class=\"qa-wrapper\" style=\"display: block\"><span class=\"show-answer collapsed\" style=\"cursor: pointer\" data-target=\"q353005\">Show Answer<\/span><\/p>\n<div id=\"q353005\" class=\"hidden-answer\" style=\"display: none\">A repressible operon uses a protein bound to the promoter region of a gene to keep the gene repressed or silent. This repressor must be actively removed in order to transcribe the gene. An inducible operon is either activated or repressed depending on the needs of the cell and what is available in the local environment.<\/div>\n<\/div>\n<\/div>\n<div class=\"textbox tryit\">\n<h3>Try It<\/h3>\n<p>\t<iframe id=\"assessment_practice_de943158-b257-45d0-8c10-be0616485bf4\" class=\"resizable\" src=\"https:\/\/assess.lumenlearning.com\/practice\/de943158-b257-45d0-8c10-be0616485bf4?iframe_resize_id=assessment_practice_id_de943158-b257-45d0-8c10-be0616485bf4\" frameborder=\"0\" style=\"border:none;width:100%;height:100%;min-height:300px;\"><br \/>\n\t<\/iframe>\n<\/div>\n\n\t\t\t <section class=\"citations-section\" role=\"contentinfo\">\n\t\t\t <h3>Candela Citations<\/h3>\n\t\t\t\t\t <div>\n\t\t\t\t\t\t <div id=\"citation-list-3289\">\n\t\t\t\t\t\t\t <div class=\"licensing\"><div class=\"license-attribution-dropdown-subheading\">CC licensed content, Shared previously<\/div><ul class=\"citation-list\"><li>Biology 2e. <strong>Provided by<\/strong>: OpenStax. <strong>Located at<\/strong>: <a target=\"_blank\" href=\"http:\/\/cnx.org\/contents\/185cbf87-c72e-48f5-b51e-f14f21b5eabd@10.8\">http:\/\/cnx.org\/contents\/185cbf87-c72e-48f5-b51e-f14f21b5eabd@10.8<\/a>. <strong>License<\/strong>: <em><a target=\"_blank\" rel=\"license\" href=\"https:\/\/creativecommons.org\/licenses\/by\/4.0\/\">CC BY: Attribution<\/a><\/em>. <strong>License Terms<\/strong>: Access for free at https:\/\/openstax.org\/books\/biology-2e\/pages\/1-introduction<\/li><\/ul><\/div>\n\t\t\t\t\t\t <\/div>\n\t\t\t\t\t <\/div>\n\t\t\t <\/section>","protected":false},"author":17,"menu_order":8,"template":"","meta":{"_candela_citation":"[{\"type\":\"cc\",\"description\":\"Biology 2e\",\"author\":\"\",\"organization\":\"OpenStax\",\"url\":\"http:\/\/cnx.org\/contents\/185cbf87-c72e-48f5-b51e-f14f21b5eabd@10.8\",\"project\":\"\",\"license\":\"cc-by\",\"license_terms\":\"Access for free at https:\/\/openstax.org\/books\/biology-2e\/pages\/1-introduction\"}]","CANDELA_OUTCOMES_GUID":"5425fe7e-a3e6-4670-a6c3-49b661b9b305, e4e06b3d-0998-45ad-a8fc-1ed961ebc049","pb_show_title":"on","pb_short_title":"","pb_subtitle":"","pb_authors":[],"pb_section_license":""},"chapter-type":[],"contributor":[],"license":[],"class_list":["post-3289","chapter","type-chapter","status-publish","hentry"],"part":3270,"_links":{"self":[{"href":"https:\/\/courses.lumenlearning.com\/wm-biology1\/wp-json\/pressbooks\/v2\/chapters\/3289","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/courses.lumenlearning.com\/wm-biology1\/wp-json\/pressbooks\/v2\/chapters"}],"about":[{"href":"https:\/\/courses.lumenlearning.com\/wm-biology1\/wp-json\/wp\/v2\/types\/chapter"}],"author":[{"embeddable":true,"href":"https:\/\/courses.lumenlearning.com\/wm-biology1\/wp-json\/wp\/v2\/users\/17"}],"version-history":[{"count":20,"href":"https:\/\/courses.lumenlearning.com\/wm-biology1\/wp-json\/pressbooks\/v2\/chapters\/3289\/revisions"}],"predecessor-version":[{"id":5997,"href":"https:\/\/courses.lumenlearning.com\/wm-biology1\/wp-json\/pressbooks\/v2\/chapters\/3289\/revisions\/5997"}],"part":[{"href":"https:\/\/courses.lumenlearning.com\/wm-biology1\/wp-json\/pressbooks\/v2\/parts\/3270"}],"metadata":[{"href":"https:\/\/courses.lumenlearning.com\/wm-biology1\/wp-json\/pressbooks\/v2\/chapters\/3289\/metadata\/"}],"wp:attachment":[{"href":"https:\/\/courses.lumenlearning.com\/wm-biology1\/wp-json\/wp\/v2\/media?parent=3289"}],"wp:term":[{"taxonomy":"chapter-type","embeddable":true,"href":"https:\/\/courses.lumenlearning.com\/wm-biology1\/wp-json\/pressbooks\/v2\/chapter-type?post=3289"},{"taxonomy":"contributor","embeddable":true,"href":"https:\/\/courses.lumenlearning.com\/wm-biology1\/wp-json\/wp\/v2\/contributor?post=3289"},{"taxonomy":"license","embeddable":true,"href":"https:\/\/courses.lumenlearning.com\/wm-biology1\/wp-json\/wp\/v2\/license?post=3289"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}