{"id":876,"date":"2018-05-03T18:36:11","date_gmt":"2018-05-03T18:36:11","guid":{"rendered":"https:\/\/courses.lumenlearning.com\/suny-osbiology2e\/chapter\/prokaryotic-transcription\/"},"modified":"2018-06-28T12:52:01","modified_gmt":"2018-06-28T12:52:01","slug":"prokaryotic-transcription","status":"publish","type":"chapter","link":"https:\/\/courses.lumenlearning.com\/suny-osbiology2e\/chapter\/prokaryotic-transcription\/","title":{"raw":"Prokaryotic Transcription","rendered":"Prokaryotic Transcription"},"content":{"raw":"<div class=\"textbox learning-objectives\">\r\n<h3>Learning Objectives<\/h3>\r\nBy the end of this section, you will be able to do the following:\r\n<ul>\r\n \t<li>List the different steps in prokaryotic transcription<\/li>\r\n \t<li>Discuss the role of promoters in prokaryotic transcription<\/li>\r\n \t<li>Describe how and when transcription is terminated<\/li>\r\n<\/ul>\r\n<\/div>\r\n<p id=\"fs-id1468209\">The prokaryotes, which include Bacteria and Archaea, are mostly single-celled organisms that, by definition, lack membrane-bound nuclei and other organelles. A bacterial chromosome is a closed circle that, unlike eukaryotic chromosomes, is not organized around histone proteins. The central region of the cell in which prokaryotic DNA resides is called the nucleoid region. In addition, prokaryotes often have abundant plasmids, which are shorter, circular DNA molecules that may only contain one or a few genes. Plasmids can be transferred independently of the bacterial chromosome during cell division and often carry traits such as those involved with antibiotic resistance.<\/p>\r\nTranscription in prokaryotes (and in eukaryotes) requires the DNA double helix to partially unwind in the region of mRNA synthesis. The region of unwinding is called a transcription bubble. Transcription always proceeds from the same DNA strand for each gene, which is called the template strand. The mRNA product is complementary to the template strand and is almost identical to the other DNA strand, called the nontemplate strand, or the coding strand. The only nucleotide difference is that in mRNA, all of the T nucleotides are replaced with U nucleotides (<a class=\"autogenerated-content\" href=\"#fig-ch15_02_02a\">(Figure)<\/a>). In an RNA double helix, A can bind U via two hydrogen bonds, just as in A\u2013T pairing in a DNA double helix.\r\n<div id=\"fig-ch15_02_02a\" class=\"wp-caption aligncenter\">\r\n\r\n[caption id=\"\" align=\"aligncenter\" width=\"420\"]<img src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/3206\/2018\/05\/03183604\/Figure_15_02_02a.png\" alt=\"Illustration shows RNA synthesis by RNA polymerase. The RNA strand is synthesized in the 5' to 3' direction.\" width=\"420\" height=\"643\" \/> <strong>Figure 1. <\/strong>Messenger RNA is a copy of protein-coding information in the coding strand of DNA, with the substitution of U in the RNA for T in the coding sequence. However, new RNA nucleotides base pair with the nucleotides of the template strand. RNA is synthesized in its 5'-3' direction, using the enzyme RNA polymerase. As the template is read, the DNA unwinds ahead of the polymerase and then rewinds behind it.[\/caption]\r\n\r\n<\/div>\r\n<p id=\"fs-id1520179\">The nucleotide pair in the DNA double helix that corresponds to the site from which the first 5' mRNA nucleotide is transcribed is called the +1 site, or the initiation site. Nucleotides preceding the initiation site are denoted with a \u201c-\u201d and are designated <em>upstream nucleotides<\/em>. Conversely, nucleotides following the initiation site are denoted with \u201c+\u201d numbering and are called <em>downstream nucleotides<\/em>.<\/p>\r\n\r\n<div id=\"fs-id2899946\" class=\"bc-section section\">\r\n<h3>Initiation of Transcription in Prokaryotes<\/h3>\r\nProkaryotes do not have membrane-enclosed nuclei. Therefore, the processes of transcription, translation, and mRNA degradation can all occur simultaneously. The intracellular level of a bacterial protein can quickly be amplified by multiple transcription and translation events that occur concurrently on the same DNA template. Prokaryotic genomes are very compact, and prokaryotic transcripts often cover more than one gene or cistron (a coding sequence for a single protein). Polycistronic mRNAs are then translated to produce more than one kind of protein.\r\n<p id=\"fs-id2117424\">Our discussion here will exemplify transcription by describing this process in <em>Escherichia coli<\/em>, a well-studied eubacterial species. Although some differences exist between transcription in <em>E. coli<\/em> and transcription in archaea, an understanding of <em>E. coli <\/em>transcription can be applied to virtually all bacterial species.<\/p>\r\n\r\n<div id=\"fs-id2016560\" class=\"bc-section section\">\r\n<h4>Prokaryotic RNA Polymerase<\/h4>\r\n<p id=\"fs-id1694517\">Prokaryotes use the same RNA polymerase to transcribe all of their genes. In <em>E. coli<\/em>, the polymerase is composed of five polypeptide subunits, two of which are identical. Four of these subunits, denoted <em>\u03b1<\/em>, <em>\u03b1<\/em>, <em>\u03b2<\/em>, and <em>\u03b2<\/em>', comprise the polymerase core enzyme. These subunits assemble every time a gene is transcribed, and they disassemble once transcription is complete. Each subunit has a unique role; the two <em>\u03b1<\/em>-subunits are necessary to assemble the polymerase on the DNA; the <em>\u03b2<\/em>-subunit binds to the ribonucleoside triphosphate that will become part of the nascent mRNA molecule; and the <em>\u03b2<\/em>' subunit binds the DNA template strand. The fifth subunit, <em>\u03c3<\/em>, is involved only in transcription initiation. It confers transcriptional specificity such that the polymerase begins to synthesize mRNA from an appropriate initiation site. Without <em>\u03c3<\/em>, the core enzyme would transcribe from random sites and would produce mRNA molecules that specified protein gibberish. The polymerase comprised of all five subunits is called the holoenzyme.<\/p>\r\n\r\n<\/div>\r\n<div class=\"bc-section section\">\r\n<h4>Prokaryotic Promoters<\/h4>\r\n<p id=\"fs-id1236812\">A promoter is a DNA sequence onto which the transcription machinery, including RNA polymerase, binds and initiates transcription. In most cases, promoters exist upstream of the genes they regulate. The specific sequence of a promoter is very important because it determines whether the corresponding gene is transcribed all the time, some of the time, or infrequently. Although promoters vary among prokaryotic genomes, a few elements are evolutionarily conserved in many species. At the -10 and -35 regions upstream of the initiation site, there are two <em>promoter consensus sequences<\/em>, or regions that are similar across all promoters and across various bacterial species (<a class=\"autogenerated-content\" href=\"#fig-ch15_02_01\">(Figure)<\/a>). The -10 sequence, called the -10 region, has the consensus sequence TATAAT. The -35 sequence has the consensus sequence TTGACA. These consensus sequences are recognized and bound by <em>\u03c3<\/em>. Once this interaction is made, the subunits of the core enzyme bind to the site. The A\u2013T-rich -10 region facilitates unwinding of the DNA template, and several phosphodiester bonds are made. The transcription initiation phase ends with the production of abortive transcripts, which are polymers of approximately 10 nucleotides that are made and released.<\/p>\r\n\r\n<div id=\"fig-ch15_02_01\" class=\"wp-caption aligncenter\">\r\n\r\n[caption id=\"\" align=\"aligncenter\" width=\"350\"]<img src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/3206\/2018\/05\/03183607\/Figure_15_02_01.jpg\" alt=\"Illustration shows the \u03c3 subunit of RNA polymerase bound to two consensus sequences that are 10 and 35 bases upstream of the transcription start site. RNA polymerase is bound to \u03c3.\" width=\"350\" height=\"243\" \/> <strong>Figure 2. <\/strong>The \u03c3 subunit of prokaryotic RNA polymerase recognizes consensus sequences found in the promoter region upstream of the transcription start site. The \u03c3 subunit dissociates from the polymerase after transcription has been initiated.[\/caption]\r\n\r\n<\/div>\r\n<div class=\"interactive textbox tryit\">\r\n<h3>Link to Learning<\/h3>\r\nView this <a href=\"http:\/\/openstaxcollege.org\/l\/transcription\" target=\"_window\">MolecularMovies animation<\/a> to see the first part of transcription and the base sequence repetition of the TATA box.\r\n\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n<div id=\"fs-id1298841\" class=\"bc-section section\">\r\n<h3>Elongation and Termination in Prokaryotes<\/h3>\r\n<p id=\"fs-id3319239\">The transcription elongation phase begins with the release of the <em>\u03c3<\/em> subunit from the polymerase. The dissociation of <em>\u03c3<\/em> allows the core enzyme to proceed along the DNA template, synthesizing mRNA in the 5' to 3' direction at a rate of approximately 40 nucleotides per second. As elongation proceeds, the DNA is continuously unwound ahead of the core enzyme and rewound behind it. The base pairing between DNA and RNA is not stable enough to maintain the stability of the mRNA synthesis components. Instead, the RNA polymerase acts as a stable linker between the DNA template and the nascent RNA strands to ensure that elongation is not interrupted prematurely.<\/p>\r\n\r\n<\/div>\r\n<div id=\"fs-id1318146\" class=\"bc-section section\">\r\n<h3>Prokaryotic Termination Signals<\/h3>\r\n<p id=\"fs-id1403735\">Once a gene is transcribed, the prokaryotic polymerase needs to be instructed to dissociate from the DNA template and liberate the newly made mRNA. Depending on the gene being transcribed, there are two kinds of termination signals. One is protein-based and the other is RNA-based. Rho-dependent termination is controlled by the rho protein, which tracks along behind the polymerase on the growing mRNA chain. Near the end of the gene, the polymerase encounters a run of G nucleotides on the DNA template and it stalls. As a result, the rho protein collides with the polymerase. The interaction with rho releases the mRNA from the transcription bubble.<\/p>\r\n<p id=\"fs-id2629848\">Rho-independent termination is controlled by specific sequences in the DNA template strand. As the polymerase nears the end of the gene being transcribed, it encounters a region rich in C\u2013G nucleotides. The mRNA folds back on itself, and the complementary C\u2013G nucleotides bind together. The result is a stable hairpin that causes the polymerase to stall as soon as it begins to transcribe a region rich in A\u2013T nucleotides. The complementary U\u2013A region of the mRNA transcript forms only a weak interaction with the template DNA. This, coupled with the stalled polymerase, induces enough instability for the core enzyme to break away and liberate the new mRNA transcript.<\/p>\r\n<p id=\"fs-id2114520\">Upon termination, the process of transcription is complete. By the time termination occurs, the prokaryotic transcript would already have been used to begin synthesis of numerous copies of the encoded protein because these processes can occur concurrently. The unification of transcription, translation, and even mRNA degradation is possible because all of these processes occur in the same 5' to 3' direction, and because there is no membranous compartmentalization in the prokaryotic cell (<a class=\"autogenerated-content\" href=\"#fig-ch15_02_03\">(Figure)<\/a>). In contrast, the presence of a nucleus in eukaryotic cells precludes simultaneous transcription and translation.<\/p>\r\n\r\n<div id=\"fig-ch15_02_03\" class=\"wp-caption aligncenter\">\r\n\r\n[caption id=\"\" align=\"aligncenter\" width=\"350\"]<img src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/3206\/2018\/05\/03183610\/Figure_15_02_03.jpg\" alt=\"Illustration shows multiple mRNAs transcribed off one gene. Ribosomes attach to the mRNA before transcription is complete and begin to make protein.\" width=\"350\" height=\"189\" \/> <strong>Figure 3. <\/strong>Multiple polymerases can transcribe a single bacterial gene while numerous ribosomes concurrently translate the mRNA transcripts into polypeptides. In this way, a specific protein can rapidly reach a high concentration in the bacterial cell.[\/caption]\r\n\r\n<\/div>\r\n<div id=\"fs-id2626015\" class=\"interactive textbox tryit\">\r\n<h3>Link to Learning<\/h3>\r\n<p id=\"fs-id2701078\">Visit this <a href=\"http:\/\/openstaxcollege.org\/l\/transcription2\" target=\"_window\"> BioStudio animation<\/a> to see the process of prokaryotic transcription.<\/p>\r\n\r\n<\/div>\r\n<\/div>\r\n<div id=\"fs-id2316839\" class=\"summary textbox key-takeaways\">\r\n<h3>Section Summary<\/h3>\r\n<p id=\"fs-id1265785\">In prokaryotes, mRNA synthesis is initiated at a promoter sequence on the DNA template comprising two consensus sequences that recruit RNA polymerase. The prokaryotic polymerase consists of a core enzyme of four protein subunits and a <em>\u03c3<\/em> protein that assists only with initiation. Elongation synthesizes mRNA in the 5' to 3' direction at a rate of 40 nucleotides per second. Termination liberates the mRNA and occurs either by rho protein interaction or by the formation of an mRNA hairpin.<\/p>\r\n\r\n<\/div>\r\n<div id=\"fs-id2642257\" class=\"multiple-choice textbox exercises\">\r\n<h3>Review Questions<\/h3>\r\n<div id=\"fs-id2914875\">\r\n<div id=\"fs-id1420578\">\r\n\r\nWhich subunit of the <em>E. coli<\/em> polymerase confers specificity to transcription?\r\n<ol type=\"a\">\r\n \t<li><em>\u03b1<\/em><\/li>\r\n \t<li><em>\u03b2<\/em><\/li>\r\n \t<li><em>\u03b2<\/em>'<\/li>\r\n \t<li><em>\u03c3<\/em><\/li>\r\n<\/ol>\r\n<\/div>\r\n[reveal-answer q=\"fs-id890335\"]Show Solution[\/reveal-answer]\r\n[hidden-answer a=\"fs-id890335\"]\r\n<div id=\"fs-id890335\">\r\n\r\nD\r\n\r\n<\/div>\r\n[\/hidden-answer]\r\n\r\n<\/div>\r\n<div id=\"fs-id1313546\">\r\n<div id=\"fs-id1957391\">\r\n<p id=\"fs-id1394141\">The -10 and -35 regions of prokaryotic promoters are called consensus sequences because ________.<\/p>\r\n\r\n<ol id=\"fs-id1704430\" type=\"a\">\r\n \t<li>they are identical in all bacterial species<\/li>\r\n \t<li>they are similar in all bacterial species<\/li>\r\n \t<li>they exist in all organisms<\/li>\r\n \t<li>they have the same function in all organisms<\/li>\r\n<\/ol>\r\n<\/div>\r\n<div>\r\n<p id=\"fs-id1605467\">[reveal-answer q=\"532830\"]Show Answer[\/reveal-answer]\r\n[hidden-answer a=\"532830\"]<\/p>\r\nB[\/hidden-answer]\r\n\r\n<\/div>\r\n<\/div>\r\n<div id=\"eip-845\">\r\n<div id=\"eip-558\">\r\n<p id=\"eip-32\">Three different bacteria species have the following consensus sequences upstream of a conserved gene.<\/p>\r\n\r\n<table id=\"eip-651\" summary=\"Three different bacteria species have the following consensus sequences upstream of a conserved gene.\">\r\n<tbody>\r\n<tr>\r\n<td><\/td>\r\n<td>Species A<\/td>\r\n<td>Species B<\/td>\r\n<td>Species C<\/td>\r\n<\/tr>\r\n<tr>\r\n<td>-10<\/td>\r\n<td>TAATAAT<\/td>\r\n<td>TTTAAT<\/td>\r\n<td>TATATT<\/td>\r\n<\/tr>\r\n<tr>\r\n<td>-35<\/td>\r\n<td>TTGACA<\/td>\r\n<td>TTGGCC<\/td>\r\n<td>TTGAAA<\/td>\r\n<\/tr>\r\n<\/tbody>\r\n<\/table>\r\n<p id=\"eip-33\">Order the bacteria from most to least efficient initiation of gene transcription.<\/p>\r\n\r\n<ol id=\"fs-listid002\" type=\"a\">\r\n \t<li>A &gt; B &gt; C<\/li>\r\n \t<li>B &gt; C &gt; A<\/li>\r\n \t<li>C &gt; B &gt; A<\/li>\r\n \t<li>A &gt; C &gt; B<\/li>\r\n<\/ol>\r\n<\/div>\r\n<div id=\"eip-146\">\r\n<p id=\"eip-469\">[reveal-answer q=\"225557\"]Show Answer[\/reveal-answer]\r\n[hidden-answer a=\"225557\"]<\/p>\r\nD[\/hidden-answer]\r\n\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n<div id=\"fs-id1387341\" class=\"free-response textbox exercises\">\r\n<h3>Free Response<\/h3>\r\n<div>\r\n<div id=\"fs-id1427093\">\r\n<p id=\"fs-id1414962\">If mRNA is complementary to the DNA template strand and the DNA template strand is complementary to the DNA nontemplate strand, then why are base sequences of mRNA and the DNA nontemplate strand not identical? Could they ever be?<\/p>\r\n\r\n<\/div>\r\n[reveal-answer q=\"fs-id1291455\"]Show Solution[\/reveal-answer]\r\n[hidden-answer a=\"fs-id1291455\"]\r\n<div id=\"fs-id1291455\">\r\n<p id=\"fs-id1432929\">DNA is different from RNA in that T nucleotides in DNA are replaced with U nucleotides in RNA. Therefore, they could never be identical in base sequence.<\/p>\r\n\r\n<\/div>\r\n[\/hidden-answer]\r\n\r\n<\/div>\r\n<div id=\"fs-id1385377\">\r\n<div>\r\n<p id=\"fs-id889896\">In your own words, describe the difference between rho-dependent and rho-independent termination of transcription in prokaryotes.<\/p>\r\n\r\n<\/div>\r\n[reveal-answer q=\"fs-id2896656\"]Show Solution[\/reveal-answer]\r\n[hidden-answer a=\"fs-id2896656\"]\r\n<div id=\"fs-id2896656\">\r\n<p id=\"fs-id1393826\">Rho-dependent termination is controlled by the rho protein, which tracks along behind the polymerase on the growing mRNA chain. Near the end of the gene, the polymerase stalls at a run of G nucleotides on the DNA template. The rho protein collides with the polymerase and releases mRNA from the transcription bubble. Rho-independent termination is controlled by specific sequences in the DNA template strand. As the polymerase nears the end of the gene being transcribed, it encounters a region rich in C\u2013G nucleotides. This creates an mRNA hairpin that causes the polymerase to stall right as it begins to transcribe a region rich in A\u2013T nucleotides. Because A\u2013U bonds are less thermostable, the core enzyme falls away.<\/p>\r\n\r\n<\/div>\r\n[\/hidden-answer]\r\n\r\n<\/div>\r\n<div id=\"eip-523\">\r\n<div id=\"eip-721\">\r\n<p id=\"eip-807\">A fragment of bacterial DNA reads:<\/p>\r\n<p id=\"eip-808\">3\u2019 \u2013TACCTATAATCTCAATTGATAGAAGCACTCTAC\u2013 5\u2019<\/p>\r\n<p id=\"eip-809\">Assuming that this fragment is the template strand, what is the sequence of mRNA that would be transcribed? (Hint: Be sure to identify the initiation site.)<\/p>\r\n[reveal-answer q=\"933973\"]Show Solution[\/reveal-answer]\r\n[hidden-answer a=\"933973\"]\r\n<p id=\"eip-846\">ACUAUCUUCGUGAGAUG<\/p>\r\n<p id=\"eip-847\">By examining the DNA sequence, we can see that there is a -10 consensus sequence near the 3\u2019 end of the fragment. If we then count downstream, the +1 initiation site is the T immediately following the sequence AAT. This means the DNA fragment that will serve as the template for transcription has the sequence TGATAGAAGCACTCTAC. The mRNA made from this template will have complimentary base pairing with uracil (U) instead of thymine (T). This gives us ACUAUCUUCGUGAGAUG as the transcribed mRNA sequence.<\/p>\r\n[\/hidden-answer]\r\n\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n<div class=\"textbox shaded\">\r\n<h3>Glossary<\/h3>\r\n<dl id=\"fs-id1414556\">\r\n \t<dt>consensus<\/dt>\r\n \t<dd id=\"fs-id1454273\">DNA sequence that is used by many species to perform the same or similar functions<\/dd>\r\n<\/dl>\r\n<dl id=\"fs-id1423662\">\r\n \t<dt>core enzyme<\/dt>\r\n \t<dd id=\"fs-id1262355\">prokaryotic RNA polymerase consisting of <em>\u03b1<\/em>, <em>\u03b1<\/em>, <em>\u03b2<\/em>, and <em>\u03b2<\/em>' but missing <em>\u03c3<\/em>; this complex performs elongation<\/dd>\r\n<\/dl>\r\n<dl id=\"fs-id1988912\">\r\n \t<dt>downstream<\/dt>\r\n \t<dd id=\"fs-id1471397\">nucleotides following the initiation site in the direction of mRNA transcription; in general, sequences that are toward the 3' end relative to a site on the mRNA<\/dd>\r\n<\/dl>\r\n<dl id=\"fs-id1569194\">\r\n \t<dt>hairpin<\/dt>\r\n \t<dd id=\"fs-id1294148\">structure of RNA when it folds back on itself and forms intramolecular hydrogen bonds between complementary nucleotides<\/dd>\r\n<\/dl>\r\n<dl id=\"fs-id1700226\">\r\n \t<dt>holoenzyme<\/dt>\r\n \t<dd id=\"fs-id1770973\">prokaryotic RNA polymerase consisting of <em>\u03b1<\/em>, <em>\u03b1<\/em>, <em>\u03b2<\/em>, <em>\u03b2<\/em>', and <em>\u03c3<\/em>; this complex is responsible for transcription initiation<\/dd>\r\n<\/dl>\r\n<dl id=\"fs-id1920696\">\r\n \t<dt>initiation site<\/dt>\r\n \t<dd id=\"fs-id2042376\">nucleotide from which mRNA synthesis proceeds in the 5' to 3' direction; denoted with a \u201c+1\u201d<\/dd>\r\n<\/dl>\r\n<dl id=\"fs-id1313517\">\r\n \t<dt>nontemplate strand<\/dt>\r\n \t<dd id=\"fs-id1560919\">strand of DNA that is not used to transcribe mRNA; this strand is identical to the mRNA except that T nucleotides in the DNA are replaced by U nucleotides in the mRNA<\/dd>\r\n<\/dl>\r\n<dl id=\"fs-id1470681\">\r\n \t<dt>plasmid<\/dt>\r\n \t<dd id=\"fs-id2010976\">extrachromosomal, covalently closed, circular DNA molecule that may only contain one or a few genes; common in prokaryotes<\/dd>\r\n<\/dl>\r\n<dl id=\"fs-id1270422\">\r\n \t<dt>promoter<\/dt>\r\n \t<dd id=\"fs-id1288688\">DNA sequence to which RNA polymerase and associated factors bind and initiate transcription<\/dd>\r\n<\/dl>\r\n<dl id=\"fs-id1340171\">\r\n \t<dt>rho-dependent termination<\/dt>\r\n \t<dd id=\"fs-id1703373\">in prokaryotes, termination of transcription by an interaction between RNA polymerase and the rho protein at a run of G nucleotides on the DNA template<\/dd>\r\n<\/dl>\r\n<dl id=\"fs-id1438024\">\r\n \t<dt>rho-independent<\/dt>\r\n \t<dd id=\"fs-id1438741\">termination sequence-dependent termination of prokaryotic mRNA synthesis; caused by hairpin formation in the mRNA that stalls the polymerase<\/dd>\r\n<\/dl>\r\n<dl id=\"fs-id1651328\">\r\n \t<dt>TATA box<\/dt>\r\n \t<dd id=\"fs-id1266812\">conserved promoter sequence in eukaryotes and prokaryotes that helps to establish the initiation site for transcription<\/dd>\r\n<\/dl>\r\n<dl id=\"fs-id2655268\">\r\n \t<dt>template strand<\/dt>\r\n \t<dd id=\"fs-id1452049\">strand of DNA that specifies the complementary mRNA molecule<\/dd>\r\n<\/dl>\r\n<dl id=\"fs-id1450421\">\r\n \t<dt>transcription bubble<\/dt>\r\n \t<dd id=\"fs-id1797681\">region of locally unwound DNA that allows for transcription of mRNA<\/dd>\r\n<\/dl>\r\n<dl id=\"fs-id1386997\">\r\n \t<dt>upstream<\/dt>\r\n \t<dd id=\"fs-id2331355\">nucleotides preceding the initiation site; in general, sequences toward the 5' end relative to a site on the mRNA<\/dd>\r\n<\/dl>\r\n<\/div>","rendered":"<div class=\"textbox learning-objectives\">\n<h3>Learning Objectives<\/h3>\n<p>By the end of this section, you will be able to do the following:<\/p>\n<ul>\n<li>List the different steps in prokaryotic transcription<\/li>\n<li>Discuss the role of promoters in prokaryotic transcription<\/li>\n<li>Describe how and when transcription is terminated<\/li>\n<\/ul>\n<\/div>\n<p id=\"fs-id1468209\">The prokaryotes, which include Bacteria and Archaea, are mostly single-celled organisms that, by definition, lack membrane-bound nuclei and other organelles. A bacterial chromosome is a closed circle that, unlike eukaryotic chromosomes, is not organized around histone proteins. The central region of the cell in which prokaryotic DNA resides is called the nucleoid region. In addition, prokaryotes often have abundant plasmids, which are shorter, circular DNA molecules that may only contain one or a few genes. Plasmids can be transferred independently of the bacterial chromosome during cell division and often carry traits such as those involved with antibiotic resistance.<\/p>\n<p>Transcription in prokaryotes (and in eukaryotes) requires the DNA double helix to partially unwind in the region of mRNA synthesis. The region of unwinding is called a transcription bubble. Transcription always proceeds from the same DNA strand for each gene, which is called the template strand. The mRNA product is complementary to the template strand and is almost identical to the other DNA strand, called the nontemplate strand, or the coding strand. The only nucleotide difference is that in mRNA, all of the T nucleotides are replaced with U nucleotides (<a class=\"autogenerated-content\" href=\"#fig-ch15_02_02a\">(Figure)<\/a>). In an RNA double helix, A can bind U via two hydrogen bonds, just as in A\u2013T pairing in a DNA double helix.<\/p>\n<div id=\"fig-ch15_02_02a\" class=\"wp-caption aligncenter\">\n<div style=\"width: 430px\" class=\"wp-caption aligncenter\"><img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/3206\/2018\/05\/03183604\/Figure_15_02_02a.png\" alt=\"Illustration shows RNA synthesis by RNA polymerase. The RNA strand is synthesized in the 5' to 3' direction.\" width=\"420\" height=\"643\" \/><\/p>\n<p class=\"wp-caption-text\"><strong>Figure 1. <\/strong>Messenger RNA is a copy of protein-coding information in the coding strand of DNA, with the substitution of U in the RNA for T in the coding sequence. However, new RNA nucleotides base pair with the nucleotides of the template strand. RNA is synthesized in its 5&#8242;-3&#8242; direction, using the enzyme RNA polymerase. As the template is read, the DNA unwinds ahead of the polymerase and then rewinds behind it.<\/p>\n<\/div>\n<\/div>\n<p id=\"fs-id1520179\">The nucleotide pair in the DNA double helix that corresponds to the site from which the first 5&#8242; mRNA nucleotide is transcribed is called the +1 site, or the initiation site. Nucleotides preceding the initiation site are denoted with a \u201c-\u201d and are designated <em>upstream nucleotides<\/em>. Conversely, nucleotides following the initiation site are denoted with \u201c+\u201d numbering and are called <em>downstream nucleotides<\/em>.<\/p>\n<div id=\"fs-id2899946\" class=\"bc-section section\">\n<h3>Initiation of Transcription in Prokaryotes<\/h3>\n<p>Prokaryotes do not have membrane-enclosed nuclei. Therefore, the processes of transcription, translation, and mRNA degradation can all occur simultaneously. The intracellular level of a bacterial protein can quickly be amplified by multiple transcription and translation events that occur concurrently on the same DNA template. Prokaryotic genomes are very compact, and prokaryotic transcripts often cover more than one gene or cistron (a coding sequence for a single protein). Polycistronic mRNAs are then translated to produce more than one kind of protein.<\/p>\n<p id=\"fs-id2117424\">Our discussion here will exemplify transcription by describing this process in <em>Escherichia coli<\/em>, a well-studied eubacterial species. Although some differences exist between transcription in <em>E. coli<\/em> and transcription in archaea, an understanding of <em>E. coli <\/em>transcription can be applied to virtually all bacterial species.<\/p>\n<div id=\"fs-id2016560\" class=\"bc-section section\">\n<h4>Prokaryotic RNA Polymerase<\/h4>\n<p id=\"fs-id1694517\">Prokaryotes use the same RNA polymerase to transcribe all of their genes. In <em>E. coli<\/em>, the polymerase is composed of five polypeptide subunits, two of which are identical. Four of these subunits, denoted <em>\u03b1<\/em>, <em>\u03b1<\/em>, <em>\u03b2<\/em>, and <em>\u03b2<\/em>&#8216;, comprise the polymerase core enzyme. These subunits assemble every time a gene is transcribed, and they disassemble once transcription is complete. Each subunit has a unique role; the two <em>\u03b1<\/em>-subunits are necessary to assemble the polymerase on the DNA; the <em>\u03b2<\/em>-subunit binds to the ribonucleoside triphosphate that will become part of the nascent mRNA molecule; and the <em>\u03b2<\/em>&#8216; subunit binds the DNA template strand. The fifth subunit, <em>\u03c3<\/em>, is involved only in transcription initiation. It confers transcriptional specificity such that the polymerase begins to synthesize mRNA from an appropriate initiation site. Without <em>\u03c3<\/em>, the core enzyme would transcribe from random sites and would produce mRNA molecules that specified protein gibberish. The polymerase comprised of all five subunits is called the holoenzyme.<\/p>\n<\/div>\n<div class=\"bc-section section\">\n<h4>Prokaryotic Promoters<\/h4>\n<p id=\"fs-id1236812\">A promoter is a DNA sequence onto which the transcription machinery, including RNA polymerase, binds and initiates transcription. In most cases, promoters exist upstream of the genes they regulate. The specific sequence of a promoter is very important because it determines whether the corresponding gene is transcribed all the time, some of the time, or infrequently. Although promoters vary among prokaryotic genomes, a few elements are evolutionarily conserved in many species. At the -10 and -35 regions upstream of the initiation site, there are two <em>promoter consensus sequences<\/em>, or regions that are similar across all promoters and across various bacterial species (<a class=\"autogenerated-content\" href=\"#fig-ch15_02_01\">(Figure)<\/a>). The -10 sequence, called the -10 region, has the consensus sequence TATAAT. The -35 sequence has the consensus sequence TTGACA. These consensus sequences are recognized and bound by <em>\u03c3<\/em>. Once this interaction is made, the subunits of the core enzyme bind to the site. The A\u2013T-rich -10 region facilitates unwinding of the DNA template, and several phosphodiester bonds are made. The transcription initiation phase ends with the production of abortive transcripts, which are polymers of approximately 10 nucleotides that are made and released.<\/p>\n<div id=\"fig-ch15_02_01\" class=\"wp-caption aligncenter\">\n<div style=\"width: 360px\" class=\"wp-caption aligncenter\"><img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/3206\/2018\/05\/03183607\/Figure_15_02_01.jpg\" alt=\"Illustration shows the \u03c3 subunit of RNA polymerase bound to two consensus sequences that are 10 and 35 bases upstream of the transcription start site. RNA polymerase is bound to \u03c3.\" width=\"350\" height=\"243\" \/><\/p>\n<p class=\"wp-caption-text\"><strong>Figure 2. <\/strong>The \u03c3 subunit of prokaryotic RNA polymerase recognizes consensus sequences found in the promoter region upstream of the transcription start site. The \u03c3 subunit dissociates from the polymerase after transcription has been initiated.<\/p>\n<\/div>\n<\/div>\n<div class=\"interactive textbox tryit\">\n<h3>Link to Learning<\/h3>\n<p>View this <a href=\"http:\/\/openstaxcollege.org\/l\/transcription\" target=\"_window\">MolecularMovies animation<\/a> to see the first part of transcription and the base sequence repetition of the TATA box.<\/p>\n<\/div>\n<\/div>\n<\/div>\n<div id=\"fs-id1298841\" class=\"bc-section section\">\n<h3>Elongation and Termination in Prokaryotes<\/h3>\n<p id=\"fs-id3319239\">The transcription elongation phase begins with the release of the <em>\u03c3<\/em> subunit from the polymerase. The dissociation of <em>\u03c3<\/em> allows the core enzyme to proceed along the DNA template, synthesizing mRNA in the 5&#8242; to 3&#8242; direction at a rate of approximately 40 nucleotides per second. As elongation proceeds, the DNA is continuously unwound ahead of the core enzyme and rewound behind it. The base pairing between DNA and RNA is not stable enough to maintain the stability of the mRNA synthesis components. Instead, the RNA polymerase acts as a stable linker between the DNA template and the nascent RNA strands to ensure that elongation is not interrupted prematurely.<\/p>\n<\/div>\n<div id=\"fs-id1318146\" class=\"bc-section section\">\n<h3>Prokaryotic Termination Signals<\/h3>\n<p id=\"fs-id1403735\">Once a gene is transcribed, the prokaryotic polymerase needs to be instructed to dissociate from the DNA template and liberate the newly made mRNA. Depending on the gene being transcribed, there are two kinds of termination signals. One is protein-based and the other is RNA-based. Rho-dependent termination is controlled by the rho protein, which tracks along behind the polymerase on the growing mRNA chain. Near the end of the gene, the polymerase encounters a run of G nucleotides on the DNA template and it stalls. As a result, the rho protein collides with the polymerase. The interaction with rho releases the mRNA from the transcription bubble.<\/p>\n<p id=\"fs-id2629848\">Rho-independent termination is controlled by specific sequences in the DNA template strand. As the polymerase nears the end of the gene being transcribed, it encounters a region rich in C\u2013G nucleotides. The mRNA folds back on itself, and the complementary C\u2013G nucleotides bind together. The result is a stable hairpin that causes the polymerase to stall as soon as it begins to transcribe a region rich in A\u2013T nucleotides. The complementary U\u2013A region of the mRNA transcript forms only a weak interaction with the template DNA. This, coupled with the stalled polymerase, induces enough instability for the core enzyme to break away and liberate the new mRNA transcript.<\/p>\n<p id=\"fs-id2114520\">Upon termination, the process of transcription is complete. By the time termination occurs, the prokaryotic transcript would already have been used to begin synthesis of numerous copies of the encoded protein because these processes can occur concurrently. The unification of transcription, translation, and even mRNA degradation is possible because all of these processes occur in the same 5&#8242; to 3&#8242; direction, and because there is no membranous compartmentalization in the prokaryotic cell (<a class=\"autogenerated-content\" href=\"#fig-ch15_02_03\">(Figure)<\/a>). In contrast, the presence of a nucleus in eukaryotic cells precludes simultaneous transcription and translation.<\/p>\n<div id=\"fig-ch15_02_03\" class=\"wp-caption aligncenter\">\n<div style=\"width: 360px\" class=\"wp-caption aligncenter\"><img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/3206\/2018\/05\/03183610\/Figure_15_02_03.jpg\" alt=\"Illustration shows multiple mRNAs transcribed off one gene. Ribosomes attach to the mRNA before transcription is complete and begin to make protein.\" width=\"350\" height=\"189\" \/><\/p>\n<p class=\"wp-caption-text\"><strong>Figure 3. <\/strong>Multiple polymerases can transcribe a single bacterial gene while numerous ribosomes concurrently translate the mRNA transcripts into polypeptides. In this way, a specific protein can rapidly reach a high concentration in the bacterial cell.<\/p>\n<\/div>\n<\/div>\n<div id=\"fs-id2626015\" class=\"interactive textbox tryit\">\n<h3>Link to Learning<\/h3>\n<p id=\"fs-id2701078\">Visit this <a href=\"http:\/\/openstaxcollege.org\/l\/transcription2\" target=\"_window\"> BioStudio animation<\/a> to see the process of prokaryotic transcription.<\/p>\n<\/div>\n<\/div>\n<div id=\"fs-id2316839\" class=\"summary textbox key-takeaways\">\n<h3>Section Summary<\/h3>\n<p id=\"fs-id1265785\">In prokaryotes, mRNA synthesis is initiated at a promoter sequence on the DNA template comprising two consensus sequences that recruit RNA polymerase. The prokaryotic polymerase consists of a core enzyme of four protein subunits and a <em>\u03c3<\/em> protein that assists only with initiation. Elongation synthesizes mRNA in the 5&#8242; to 3&#8242; direction at a rate of 40 nucleotides per second. Termination liberates the mRNA and occurs either by rho protein interaction or by the formation of an mRNA hairpin.<\/p>\n<\/div>\n<div id=\"fs-id2642257\" class=\"multiple-choice textbox exercises\">\n<h3>Review Questions<\/h3>\n<div id=\"fs-id2914875\">\n<div id=\"fs-id1420578\">\n<p>Which subunit of the <em>E. coli<\/em> polymerase confers specificity to transcription?<\/p>\n<ol type=\"a\">\n<li><em>\u03b1<\/em><\/li>\n<li><em>\u03b2<\/em><\/li>\n<li><em>\u03b2<\/em>&#8216;<\/li>\n<li><em>\u03c3<\/em><\/li>\n<\/ol>\n<\/div>\n<div class=\"qa-wrapper\" style=\"display: block\"><span class=\"show-answer collapsed\" style=\"cursor: pointer\" data-target=\"qfs-id890335\">Show Solution<\/span><\/p>\n<div id=\"qfs-id890335\" class=\"hidden-answer\" style=\"display: none\">\n<div id=\"fs-id890335\">\n<p>D<\/p>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n<div id=\"fs-id1313546\">\n<div id=\"fs-id1957391\">\n<p id=\"fs-id1394141\">The -10 and -35 regions of prokaryotic promoters are called consensus sequences because ________.<\/p>\n<ol id=\"fs-id1704430\" type=\"a\">\n<li>they are identical in all bacterial species<\/li>\n<li>they are similar in all bacterial species<\/li>\n<li>they exist in all organisms<\/li>\n<li>they have the same function in all organisms<\/li>\n<\/ol>\n<\/div>\n<div>\n<p id=\"fs-id1605467\">\n<div class=\"qa-wrapper\" style=\"display: block\"><span class=\"show-answer collapsed\" style=\"cursor: pointer\" data-target=\"q532830\">Show Answer<\/span><\/p>\n<div id=\"q532830\" class=\"hidden-answer\" style=\"display: none\">\n<p>B<\/p><\/div>\n<\/div>\n<\/div>\n<\/div>\n<div id=\"eip-845\">\n<div id=\"eip-558\">\n<p id=\"eip-32\">Three different bacteria species have the following consensus sequences upstream of a conserved gene.<\/p>\n<table id=\"eip-651\" summary=\"Three different bacteria species have the following consensus sequences upstream of a conserved gene.\">\n<tbody>\n<tr>\n<td><\/td>\n<td>Species A<\/td>\n<td>Species B<\/td>\n<td>Species C<\/td>\n<\/tr>\n<tr>\n<td>-10<\/td>\n<td>TAATAAT<\/td>\n<td>TTTAAT<\/td>\n<td>TATATT<\/td>\n<\/tr>\n<tr>\n<td>-35<\/td>\n<td>TTGACA<\/td>\n<td>TTGGCC<\/td>\n<td>TTGAAA<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<p id=\"eip-33\">Order the bacteria from most to least efficient initiation of gene transcription.<\/p>\n<ol id=\"fs-listid002\" type=\"a\">\n<li>A &gt; B &gt; C<\/li>\n<li>B &gt; C &gt; A<\/li>\n<li>C &gt; B &gt; A<\/li>\n<li>A &gt; C &gt; B<\/li>\n<\/ol>\n<\/div>\n<div id=\"eip-146\">\n<p id=\"eip-469\">\n<div class=\"qa-wrapper\" style=\"display: block\"><span class=\"show-answer collapsed\" style=\"cursor: pointer\" data-target=\"q225557\">Show Answer<\/span><\/p>\n<div id=\"q225557\" class=\"hidden-answer\" style=\"display: none\">\n<p>D<\/p><\/div>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n<div id=\"fs-id1387341\" class=\"free-response textbox exercises\">\n<h3>Free Response<\/h3>\n<div>\n<div id=\"fs-id1427093\">\n<p id=\"fs-id1414962\">If mRNA is complementary to the DNA template strand and the DNA template strand is complementary to the DNA nontemplate strand, then why are base sequences of mRNA and the DNA nontemplate strand not identical? Could they ever be?<\/p>\n<\/div>\n<div class=\"qa-wrapper\" style=\"display: block\"><span class=\"show-answer collapsed\" style=\"cursor: pointer\" data-target=\"qfs-id1291455\">Show Solution<\/span><\/p>\n<div id=\"qfs-id1291455\" class=\"hidden-answer\" style=\"display: none\">\n<div id=\"fs-id1291455\">\n<p id=\"fs-id1432929\">DNA is different from RNA in that T nucleotides in DNA are replaced with U nucleotides in RNA. Therefore, they could never be identical in base sequence.<\/p>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n<div id=\"fs-id1385377\">\n<div>\n<p id=\"fs-id889896\">In your own words, describe the difference between rho-dependent and rho-independent termination of transcription in prokaryotes.<\/p>\n<\/div>\n<div class=\"qa-wrapper\" style=\"display: block\"><span class=\"show-answer collapsed\" style=\"cursor: pointer\" data-target=\"qfs-id2896656\">Show Solution<\/span><\/p>\n<div id=\"qfs-id2896656\" class=\"hidden-answer\" style=\"display: none\">\n<div id=\"fs-id2896656\">\n<p id=\"fs-id1393826\">Rho-dependent termination is controlled by the rho protein, which tracks along behind the polymerase on the growing mRNA chain. Near the end of the gene, the polymerase stalls at a run of G nucleotides on the DNA template. The rho protein collides with the polymerase and releases mRNA from the transcription bubble. Rho-independent termination is controlled by specific sequences in the DNA template strand. As the polymerase nears the end of the gene being transcribed, it encounters a region rich in C\u2013G nucleotides. This creates an mRNA hairpin that causes the polymerase to stall right as it begins to transcribe a region rich in A\u2013T nucleotides. Because A\u2013U bonds are less thermostable, the core enzyme falls away.<\/p>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n<div id=\"eip-523\">\n<div id=\"eip-721\">\n<p id=\"eip-807\">A fragment of bacterial DNA reads:<\/p>\n<p id=\"eip-808\">3\u2019 \u2013TACCTATAATCTCAATTGATAGAAGCACTCTAC\u2013 5\u2019<\/p>\n<p id=\"eip-809\">Assuming that this fragment is the template strand, what is the sequence of mRNA that would be transcribed? (Hint: Be sure to identify the initiation site.)<\/p>\n<div class=\"qa-wrapper\" style=\"display: block\"><span class=\"show-answer collapsed\" style=\"cursor: pointer\" data-target=\"q933973\">Show Solution<\/span><\/p>\n<div id=\"q933973\" class=\"hidden-answer\" style=\"display: none\">\n<p id=\"eip-846\">ACUAUCUUCGUGAGAUG<\/p>\n<p id=\"eip-847\">By examining the DNA sequence, we can see that there is a -10 consensus sequence near the 3\u2019 end of the fragment. If we then count downstream, the +1 initiation site is the T immediately following the sequence AAT. This means the DNA fragment that will serve as the template for transcription has the sequence TGATAGAAGCACTCTAC. The mRNA made from this template will have complimentary base pairing with uracil (U) instead of thymine (T). This gives us ACUAUCUUCGUGAGAUG as the transcribed mRNA sequence.<\/p>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n<div class=\"textbox shaded\">\n<h3>Glossary<\/h3>\n<dl id=\"fs-id1414556\">\n<dt>consensus<\/dt>\n<dd id=\"fs-id1454273\">DNA sequence that is used by many species to perform the same or similar functions<\/dd>\n<\/dl>\n<dl id=\"fs-id1423662\">\n<dt>core enzyme<\/dt>\n<dd id=\"fs-id1262355\">prokaryotic RNA polymerase consisting of <em>\u03b1<\/em>, <em>\u03b1<\/em>, <em>\u03b2<\/em>, and <em>\u03b2<\/em>&#8216; but missing <em>\u03c3<\/em>; this complex performs elongation<\/dd>\n<\/dl>\n<dl id=\"fs-id1988912\">\n<dt>downstream<\/dt>\n<dd id=\"fs-id1471397\">nucleotides following the initiation site in the direction of mRNA transcription; in general, sequences that are toward the 3&#8242; end relative to a site on the mRNA<\/dd>\n<\/dl>\n<dl id=\"fs-id1569194\">\n<dt>hairpin<\/dt>\n<dd id=\"fs-id1294148\">structure of RNA when it folds back on itself and forms intramolecular hydrogen bonds between complementary nucleotides<\/dd>\n<\/dl>\n<dl id=\"fs-id1700226\">\n<dt>holoenzyme<\/dt>\n<dd id=\"fs-id1770973\">prokaryotic RNA polymerase consisting of <em>\u03b1<\/em>, <em>\u03b1<\/em>, <em>\u03b2<\/em>, <em>\u03b2<\/em>&#8216;, and <em>\u03c3<\/em>; this complex is responsible for transcription initiation<\/dd>\n<\/dl>\n<dl id=\"fs-id1920696\">\n<dt>initiation site<\/dt>\n<dd id=\"fs-id2042376\">nucleotide from which mRNA synthesis proceeds in the 5&#8242; to 3&#8242; direction; denoted with a \u201c+1\u201d<\/dd>\n<\/dl>\n<dl id=\"fs-id1313517\">\n<dt>nontemplate strand<\/dt>\n<dd id=\"fs-id1560919\">strand of DNA that is not used to transcribe mRNA; this strand is identical to the mRNA except that T nucleotides in the DNA are replaced by U nucleotides in the mRNA<\/dd>\n<\/dl>\n<dl id=\"fs-id1470681\">\n<dt>plasmid<\/dt>\n<dd id=\"fs-id2010976\">extrachromosomal, covalently closed, circular DNA molecule that may only contain one or a few genes; common in prokaryotes<\/dd>\n<\/dl>\n<dl id=\"fs-id1270422\">\n<dt>promoter<\/dt>\n<dd id=\"fs-id1288688\">DNA sequence to which RNA polymerase and associated factors bind and initiate transcription<\/dd>\n<\/dl>\n<dl id=\"fs-id1340171\">\n<dt>rho-dependent termination<\/dt>\n<dd id=\"fs-id1703373\">in prokaryotes, termination of transcription by an interaction between RNA polymerase and the rho protein at a run of G nucleotides on the DNA template<\/dd>\n<\/dl>\n<dl id=\"fs-id1438024\">\n<dt>rho-independent<\/dt>\n<dd id=\"fs-id1438741\">termination sequence-dependent termination of prokaryotic mRNA synthesis; caused by hairpin formation in the mRNA that stalls the polymerase<\/dd>\n<\/dl>\n<dl id=\"fs-id1651328\">\n<dt>TATA box<\/dt>\n<dd id=\"fs-id1266812\">conserved promoter sequence in eukaryotes and prokaryotes that helps to establish the initiation site for transcription<\/dd>\n<\/dl>\n<dl id=\"fs-id2655268\">\n<dt>template strand<\/dt>\n<dd id=\"fs-id1452049\">strand of DNA that specifies the complementary mRNA molecule<\/dd>\n<\/dl>\n<dl id=\"fs-id1450421\">\n<dt>transcription bubble<\/dt>\n<dd id=\"fs-id1797681\">region of locally unwound DNA that allows for transcription of mRNA<\/dd>\n<\/dl>\n<dl id=\"fs-id1386997\">\n<dt>upstream<\/dt>\n<dd id=\"fs-id2331355\">nucleotides preceding the initiation site; in general, sequences toward the 5&#8242; end relative to a site on the mRNA<\/dd>\n<\/dl>\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-876\">\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=\"https:\/\/openstax.org\/details\/books\/biology-2e\">https:\/\/openstax.org\/details\/books\/biology-2e<\/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>: Download for free at http:\/\/cnx.org\/contents\/8d50a0af-948b-4204-a71d-4826cba765b8@8.19<\/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":311,"menu_order":3,"template":"","meta":{"_candela_citation":"[{\"type\":\"cc\",\"description\":\"Biology 2e\",\"author\":\"\",\"organization\":\"OpenStax\",\"url\":\"https:\/\/openstax.org\/details\/books\/biology-2e\",\"project\":\"\",\"license\":\"cc-by\",\"license_terms\":\"Download for free at http:\/\/cnx.org\/contents\/8d50a0af-948b-4204-a71d-4826cba765b8@8.19\"}]","CANDELA_OUTCOMES_GUID":"","pb_show_title":"on","pb_short_title":"","pb_subtitle":"","pb_authors":[],"pb_section_license":""},"chapter-type":[],"contributor":[],"license":[],"class_list":["post-876","chapter","type-chapter","status-publish","hentry"],"part":864,"_links":{"self":[{"href":"https:\/\/courses.lumenlearning.com\/suny-osbiology2e\/wp-json\/pressbooks\/v2\/chapters\/876","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/courses.lumenlearning.com\/suny-osbiology2e\/wp-json\/pressbooks\/v2\/chapters"}],"about":[{"href":"https:\/\/courses.lumenlearning.com\/suny-osbiology2e\/wp-json\/wp\/v2\/types\/chapter"}],"author":[{"embeddable":true,"href":"https:\/\/courses.lumenlearning.com\/suny-osbiology2e\/wp-json\/wp\/v2\/users\/311"}],"version-history":[{"count":3,"href":"https:\/\/courses.lumenlearning.com\/suny-osbiology2e\/wp-json\/pressbooks\/v2\/chapters\/876\/revisions"}],"predecessor-version":[{"id":2520,"href":"https:\/\/courses.lumenlearning.com\/suny-osbiology2e\/wp-json\/pressbooks\/v2\/chapters\/876\/revisions\/2520"}],"part":[{"href":"https:\/\/courses.lumenlearning.com\/suny-osbiology2e\/wp-json\/pressbooks\/v2\/parts\/864"}],"metadata":[{"href":"https:\/\/courses.lumenlearning.com\/suny-osbiology2e\/wp-json\/pressbooks\/v2\/chapters\/876\/metadata\/"}],"wp:attachment":[{"href":"https:\/\/courses.lumenlearning.com\/suny-osbiology2e\/wp-json\/wp\/v2\/media?parent=876"}],"wp:term":[{"taxonomy":"chapter-type","embeddable":true,"href":"https:\/\/courses.lumenlearning.com\/suny-osbiology2e\/wp-json\/pressbooks\/v2\/chapter-type?post=876"},{"taxonomy":"contributor","embeddable":true,"href":"https:\/\/courses.lumenlearning.com\/suny-osbiology2e\/wp-json\/wp\/v2\/contributor?post=876"},{"taxonomy":"license","embeddable":true,"href":"https:\/\/courses.lumenlearning.com\/suny-osbiology2e\/wp-json\/wp\/v2\/license?post=876"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}