{"id":3547,"date":"2016-11-17T00:17:34","date_gmt":"2016-11-17T00:17:34","guid":{"rendered":"https:\/\/courses.lumenlearning.com\/wm-biology1\/?post_type=chapter&#038;p=3547"},"modified":"2024-04-29T16:30:35","modified_gmt":"2024-04-29T16:30:35","slug":"reading-repressors","status":"publish","type":"chapter","link":"https:\/\/courses.lumenlearning.com\/wm-biology1\/chapter\/reading-repressors\/","title":{"raw":"Repressors","rendered":"Repressors"},"content":{"raw":"<div class=\"textbox learning-objectives\">\r\n<h3>Learning Outcomes<\/h3>\r\n<ul>\r\n \t<li>Explain the roles of repressors in negative gene regulation<\/li>\r\n<\/ul>\r\n<\/div>\r\n<h2>Tryptophan Operon: A Repressor Operon<\/h2>\r\nBacteria such as <em>E. coli<\/em> need amino acids to survive. <strong>Tryptophan<\/strong> is one such amino acid that <em>E. coli<\/em> can ingest from the environment. <em>E. coli<\/em> can also synthesize tryptophan using enzymes that are encoded by five genes. These five genes are next to each other in what is called the <strong>tryptophan (<em>trp<\/em>) operon<\/strong> (Figure 1). If tryptophan is present in the environment, then <em>E. coli<\/em> does not need to synthesize it and the switch controlling the activation of the genes in the <em>trp<\/em> operon is switched off. However, when tryptophan availability is low, the switch controlling the operon is turned on, transcription is initiated, the genes are expressed, and tryptophan is synthesized.\r\n\r\n[caption id=\"attachment_3555\" align=\"aligncenter\" width=\"800\"]<img class=\"wp-image-3555 size-full\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/1087\/2016\/11\/17161752\/Figure_16_02_01.jpg\" alt=\"The trp operon has a promoter, an operator, and five genes named trpE, trpD, trpC, trpB, and trpA that are located in sequential order on the DNA. RNA polymerase binds to the promoter. When tryptophan is present, the trp repressor binds the operator and prevents the RNA polymerase from moving past the operator; therefore, RNA synthesis is blocked. In the absence of tryptophan, the repressor dissociates from the operator. RNA polymerase can now slide past the operator, and transcription begins.\" width=\"800\" height=\"523\" \/> Figure 1. The five genes that are needed to synthesize tryptophan in <em>E. coli<\/em> are located next to each other in the <em>trp<\/em> operon. When tryptophan is plentiful, two tryptophan molecules bind the repressor protein at the operator sequence. This physically blocks the RNA polymerase from transcribing the tryptophan genes. When tryptophan is absent, the repressor protein does not bind to the operator and the genes are transcribed.[\/caption]\r\n<p id=\"fs-idm174533984\">The\u00a0<em data-effect=\"italics\">trp<\/em>\u00a0operon includes three important regions: the coding region, the\u00a0<em data-effect=\"italics\">trp<\/em>\u00a0operator and the\u00a0<em data-effect=\"italics\">trp<\/em>\u00a0promoter. The coding region includes the genes for the five tryptophan biosynthesis enzymes. Just before the coding region is the\u00a0<strong><span id=\"term596\" data-type=\"term\">transcriptional start site<\/span><\/strong>. The promoter sequence, to which RNA polymerase binds to initiate transcription, is before or \u201cupstream\u201d of the transcriptional start site. Between the promoter and the transcriptional start site is the operator region.<\/p>\r\n<p id=\"fs-idm199850336\">The\u00a0<em data-effect=\"italics\">trp<\/em>\u00a0<strong><span id=\"term597\" data-type=\"term\">operator<\/span><\/strong>\u00a0contains the DNA code to which the\u00a0<em data-effect=\"italics\">trp<\/em>\u00a0repressor protein can bind. However, the repressor alone cannot bind to the operator. When tryptophan is present in the cell, two tryptophan molecules bind to the\u00a0<em data-effect=\"italics\">trp<\/em>\u00a0repressor, which changes the shape of the repressor protein to a form that can bind to the\u00a0<em data-effect=\"italics\">trp<\/em>\u00a0operator. Binding of the tryptophan\u2013repressor complex at the operator physically prevents the RNA polymerase from binding to the promoter and transcribing the downstream genes.<\/p>\r\n<p id=\"fs-idm101642592\">When tryptophan is not present in the cell, the repressor by itself does not bind to the operator, the polymerase can transcribe the enzyme genes, and tryptophan is synthesized. Because the repressor protein actively binds to the operator to keep the genes turned off, the\u00a0<em data-effect=\"italics\">trp<\/em>\u00a0operon is said to be\u00a0<em data-effect=\"italics\">negatively regulated<\/em>\u00a0and the proteins that bind to the operator to silence\u00a0<em data-effect=\"italics\">trp<\/em>\u00a0expression are\u00a0<strong><span id=\"term598\" data-type=\"term\">negative regulators<\/span><\/strong>.<\/p>\r\n\r\n<div class=\"textbox shaded\">\r\n\r\nWatch this video to learn more about the <em>trp<\/em> operon.\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=4409382&amp;p3sdk_version=1.10.1&amp;p=20361&amp;pt=573&amp;video_id=8aAYtMa3GFU&amp;video_target=tpm-plugin-p7c2k0s9-8aAYtMa3GFU\" 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\/operontrp_transcription.txt\" target=\"_blank\" rel=\"noopener\">view the transcript for \"operon Trp\" here (opens in new window)<\/a>.\r\n\r\n<\/div>\r\n<div class=\"textbox tryit\">\r\n<h3>Try It<\/h3>\r\nhttps:\/\/assess.lumenlearning.com\/practice\/9980d374-be0a-40a6-a60a-58cfe78e322d\r\n<\/div>","rendered":"<div class=\"textbox learning-objectives\">\n<h3>Learning Outcomes<\/h3>\n<ul>\n<li>Explain the roles of repressors in negative gene regulation<\/li>\n<\/ul>\n<\/div>\n<h2>Tryptophan Operon: A Repressor Operon<\/h2>\n<p>Bacteria such as <em>E. coli<\/em> need amino acids to survive. <strong>Tryptophan<\/strong> is one such amino acid that <em>E. coli<\/em> can ingest from the environment. <em>E. coli<\/em> can also synthesize tryptophan using enzymes that are encoded by five genes. These five genes are next to each other in what is called the <strong>tryptophan (<em>trp<\/em>) operon<\/strong> (Figure 1). If tryptophan is present in the environment, then <em>E. coli<\/em> does not need to synthesize it and the switch controlling the activation of the genes in the <em>trp<\/em> operon is switched off. However, when tryptophan availability is low, the switch controlling the operon is turned on, transcription is initiated, the genes are expressed, and tryptophan is synthesized.<\/p>\n<div id=\"attachment_3555\" style=\"width: 810px\" class=\"wp-caption aligncenter\"><img loading=\"lazy\" decoding=\"async\" aria-describedby=\"caption-attachment-3555\" class=\"wp-image-3555 size-full\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/1087\/2016\/11\/17161752\/Figure_16_02_01.jpg\" alt=\"The trp operon has a promoter, an operator, and five genes named trpE, trpD, trpC, trpB, and trpA that are located in sequential order on the DNA. RNA polymerase binds to the promoter. When tryptophan is present, the trp repressor binds the operator and prevents the RNA polymerase from moving past the operator; therefore, RNA synthesis is blocked. In the absence of tryptophan, the repressor dissociates from the operator. RNA polymerase can now slide past the operator, and transcription begins.\" width=\"800\" height=\"523\" \/><\/p>\n<p id=\"caption-attachment-3555\" class=\"wp-caption-text\">Figure 1. The five genes that are needed to synthesize tryptophan in <em>E. coli<\/em> are located next to each other in the <em>trp<\/em> operon. When tryptophan is plentiful, two tryptophan molecules bind the repressor protein at the operator sequence. This physically blocks the RNA polymerase from transcribing the tryptophan genes. When tryptophan is absent, the repressor protein does not bind to the operator and the genes are transcribed.<\/p>\n<\/div>\n<p id=\"fs-idm174533984\">The\u00a0<em data-effect=\"italics\">trp<\/em>\u00a0operon includes three important regions: the coding region, the\u00a0<em data-effect=\"italics\">trp<\/em>\u00a0operator and the\u00a0<em data-effect=\"italics\">trp<\/em>\u00a0promoter. The coding region includes the genes for the five tryptophan biosynthesis enzymes. Just before the coding region is the\u00a0<strong><span id=\"term596\" data-type=\"term\">transcriptional start site<\/span><\/strong>. The promoter sequence, to which RNA polymerase binds to initiate transcription, is before or \u201cupstream\u201d of the transcriptional start site. Between the promoter and the transcriptional start site is the operator region.<\/p>\n<p id=\"fs-idm199850336\">The\u00a0<em data-effect=\"italics\">trp<\/em>\u00a0<strong><span id=\"term597\" data-type=\"term\">operator<\/span><\/strong>\u00a0contains the DNA code to which the\u00a0<em data-effect=\"italics\">trp<\/em>\u00a0repressor protein can bind. However, the repressor alone cannot bind to the operator. When tryptophan is present in the cell, two tryptophan molecules bind to the\u00a0<em data-effect=\"italics\">trp<\/em>\u00a0repressor, which changes the shape of the repressor protein to a form that can bind to the\u00a0<em data-effect=\"italics\">trp<\/em>\u00a0operator. Binding of the tryptophan\u2013repressor complex at the operator physically prevents the RNA polymerase from binding to the promoter and transcribing the downstream genes.<\/p>\n<p id=\"fs-idm101642592\">When tryptophan is not present in the cell, the repressor by itself does not bind to the operator, the polymerase can transcribe the enzyme genes, and tryptophan is synthesized. Because the repressor protein actively binds to the operator to keep the genes turned off, the\u00a0<em data-effect=\"italics\">trp<\/em>\u00a0operon is said to be\u00a0<em data-effect=\"italics\">negatively regulated<\/em>\u00a0and the proteins that bind to the operator to silence\u00a0<em data-effect=\"italics\">trp<\/em>\u00a0expression are\u00a0<strong><span id=\"term598\" data-type=\"term\">negative regulators<\/span><\/strong>.<\/p>\n<div class=\"textbox shaded\">\n<p>Watch this video to learn more about the <em>trp<\/em> operon.<\/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=4409382&amp;p3sdk_version=1.10.1&amp;p=20361&amp;pt=573&amp;video_id=8aAYtMa3GFU&amp;video_target=tpm-plugin-p7c2k0s9-8aAYtMa3GFU\" 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\/operontrp_transcription.txt\" target=\"_blank\" rel=\"noopener\">view the transcript for &#8220;operon Trp&#8221; here (opens in new window)<\/a>.<\/p>\n<\/div>\n<div class=\"textbox tryit\">\n<h3>Try It<\/h3>\n<p>\t<iframe id=\"assessment_practice_9980d374-be0a-40a6-a60a-58cfe78e322d\" class=\"resizable\" src=\"https:\/\/assess.lumenlearning.com\/practice\/9980d374-be0a-40a6-a60a-58cfe78e322d?iframe_resize_id=assessment_practice_id_9980d374-be0a-40a6-a60a-58cfe78e322d\" 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-3547\">\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":7,"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, 5ded5ead-4b4f-41b2-9c61-d560842eef6b","pb_show_title":"on","pb_short_title":"","pb_subtitle":"","pb_authors":[],"pb_section_license":""},"chapter-type":[],"contributor":[],"license":[],"class_list":["post-3547","chapter","type-chapter","status-publish","hentry"],"part":3270,"_links":{"self":[{"href":"https:\/\/courses.lumenlearning.com\/wm-biology1\/wp-json\/pressbooks\/v2\/chapters\/3547","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":14,"href":"https:\/\/courses.lumenlearning.com\/wm-biology1\/wp-json\/pressbooks\/v2\/chapters\/3547\/revisions"}],"predecessor-version":[{"id":5996,"href":"https:\/\/courses.lumenlearning.com\/wm-biology1\/wp-json\/pressbooks\/v2\/chapters\/3547\/revisions\/5996"}],"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\/3547\/metadata\/"}],"wp:attachment":[{"href":"https:\/\/courses.lumenlearning.com\/wm-biology1\/wp-json\/wp\/v2\/media?parent=3547"}],"wp:term":[{"taxonomy":"chapter-type","embeddable":true,"href":"https:\/\/courses.lumenlearning.com\/wm-biology1\/wp-json\/pressbooks\/v2\/chapter-type?post=3547"},{"taxonomy":"contributor","embeddable":true,"href":"https:\/\/courses.lumenlearning.com\/wm-biology1\/wp-json\/wp\/v2\/contributor?post=3547"},{"taxonomy":"license","embeddable":true,"href":"https:\/\/courses.lumenlearning.com\/wm-biology1\/wp-json\/wp\/v2\/license?post=3547"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}