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<span>What is noncoding DNA?</span>
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<h1>What is noncoding DNA?</h1>
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<section><div class="mp-content"><p>Only about 1 percent of DNA is made up of protein-coding genes; the other 99 percent is noncoding. Noncoding DNA does not provide instructions for making proteins. Scientists once thought noncoding DNA was “junk,” with no known purpose. However, it is becoming clear that at least some of it is integral to the function of cells, particularly the control of gene activity. For example, noncoding DNA contains sequences that act as regulatory elements, determining when and where genes are turned on and off. Such elements provide sites for specialized proteins (called transcription factors) to attach (bind) and either activate or repress the process by which the information from genes is turned into proteins (transcription). Noncoding DNA contains many types of regulatory elements:</p>
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<ul>
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<li>
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<p>Promoters provide binding sites for the protein machinery that carries out transcription. Promoters are typically found just ahead of the gene on the DNA strand.</p>
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</li>
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<li>
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<p>Enhancers provide binding sites for proteins that help activate transcription. Enhancers can be found on the DNA strand before or after the gene they control, sometimes far away.</p>
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</li>
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<li>
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<p>Silencers provide binding sites for proteins that repress transcription. Like enhancers, silencers can be found before or after the gene they control and can be some distance away on the DNA strand.</p>
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</li>
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<li>
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<p>Insulators provide binding sites for proteins that control transcription in a number of ways. Some prevent enhancers from aiding in transcription (enhancer-blocker insulators). Others prevent structural changes in the DNA that repress gene activity (barrier insulators). Some insulators can function as both an enhancer blocker and a barrier.</p>
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</li>
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<p>Other regions of noncoding DNA provide instructions for the formation of certain kinds of RNA molecules. RNA is a chemical cousin of DNA. Examples of specialized RNA molecules produced from noncoding DNA include
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<a class="image-modal" data-alt="Transfer RNA (tRNA) is a small RNA molecule that participates in protein synthesis." data-caption="Transfer RNA (tRNA) is a small RNA molecule that participates in protein synthesis. Each tRNA molecule has two important areas: a trinucleotide region called the anticodon and a region for attaching a specific amino acid. During translation, each time an amino acid is added to the growing chain, a tRNA molecule forms base pairs with its complementary sequence on the messenger RNA (mRNA) molecule, ensuring that the appropriate amino acid is inserted into the protein." data-credit="Darryl Leja, NHGRI" data-filepath="images/PX0000HK_PRESENTATION.jpeg" data-imgtype="genetics" data-pix="PX0000HK" data-sourceurl="" data-title="Transfer RNA (tRNA)" href="https://medlineplus.gov/images/PX0000HK_PRESENTATION.jpeg" id="PX0000HK_1" title="Show image">transfer RNAs<img alt="" aria-hidden="true" class="image-modal-icon" src="https://medlineplus.gov/css/img/icon_camera_small.png"/></a>
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(tRNAs) and
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<a class="image-modal" data-alt="The mRNA strand is surrounded by the large ribosomal subunit and the small ribosomal subunit. tRNA, working with the large ribosomal subunit, adds a peptide to the growing polypeptide chain." data-caption="" data-credit="Alila Medical Media/Shutterstock.com" data-filepath="images/PX0000Q4_PRESENTATION.jpeg" data-imgtype="genetics" data-pix="PX0000Q4" data-sourceurl="" data-title="Ribosome interacting with RNA molecules to advance protein translation" href="https://medlineplus.gov/images/PX0000Q4_PRESENTATION.jpeg" id="PX0000Q4_2" title="Show image">ribosomal RNAs<img alt="" aria-hidden="true" class="image-modal-icon" src="https://medlineplus.gov/css/img/icon_camera_small.png"/></a>
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(rRNAs), which help assemble protein building blocks (amino acids) into a chain that forms a protein; microRNAs (miRNAs), which are short lengths of RNA that block the process of protein production; and long noncoding RNAs (lncRNAs), which are longer lengths of RNA that have diverse roles in regulating gene activity.</p>
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<p>Some structural elements of chromosomes are also part of noncoding DNA. For example, repeated noncoding DNA sequences at the ends of chromosomes form
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<a class="image-modal" data-alt="Image of a cell containing chromosomes; inset shows a single chromosome with centromere and telomeres labeled." data-caption="" data-credit="Darryl Leja, NHGRI" data-filepath="images/PX0000JS_PRESENTATION.jpeg" data-imgtype="genetics" data-pix="PX0000JS" data-sourceurl="" data-title="Telomeres" href="https://medlineplus.gov/images/PX0000JS_PRESENTATION.jpeg" id="PX0000JS_3" title="Show image">telomeres<img alt="" aria-hidden="true" class="image-modal-icon" src="https://medlineplus.gov/css/img/icon_camera_small.png"/></a>.
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Telomeres protect the ends of chromosomes from being degraded during the copying of genetic material. Repetitive noncoding DNA sequences also form satellite DNA, which is a part of other structural elements. Satellite DNA is the basis of the centromere, which is the constriction point of the X-shaped chromosome pair. Satellite DNA also forms heterochromatin, which is densely packed DNA that is important for controlling gene activity and maintaining the structure of chromosomes.</p>
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<p>Some noncoding DNA regions, called introns, are located within protein-coding genes but are removed before a protein is made. Regulatory elements, such as enhancers, can be located in introns. Other noncoding regions are found between genes and are known as intergenic regions.</p>
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<p>The identity of regulatory elements and other functional regions in noncoding DNA is not completely understood. Researchers are working to understand the location and role of these genetic components.</p>
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<h2>Scientific journal articles for further reading</h2>
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<p>Maston GA, Evans SK, Green MR. Transcriptional regulatory elements in the human genome. Annu Rev Genomics Hum Genet. 2006;7:29-59. Review. PubMed: <a href="https://www.ncbi.nlm.nih.gov/pubmed/16719718" target="_blank">16719718</a>.</p>
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<p>ENCODE Project Consortium. An integrated encyclopedia of DNA elements in the human genome. Nature. 2012 Sep 6;489(7414):57-74. doi: 10.1038/nature11247. PubMed: <a href="https://www.ncbi.nlm.nih.gov/pubmed/22955616" target="_blank">22955616</a>; Free full text available from PubMed Central: <a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3439153/" target="_blank">PMC3439153</a>.</p>
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<p>Plank JL, Dean A. Enhancer function: mechanistic and genome-wide insights come together. Mol Cell. 2014 Jul 3;55(1):5-14. doi: 10.1016/j.molcel.2014.06.015. Review. PubMed: <a href="https://www.ncbi.nlm.nih.gov/pubmed/24996062" target="_blank">24996062</a>.</p></div>
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</section>
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<aside>
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<section><div class="side-section"><div class="mp-content"><div class="section-header long-header">
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<h2>For more information about noncoding DNA:</h2>
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</div>
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||
<div class="section-body">
|
||
<p>Cold Spring Harbor Laboratory DNA Learning Center: <a href="https://dnalc.cshl.edu/view/15486-The-human-genome-genes-and-non-coding-DNA-3D-animation-with-basic-narration.html" target="_blank">The Human Genome: Genes and Non-coding DNA, 3D Animation with Basic Narration</a>
|
||
</p>
|
||
<p>University of Leicester Virtual Genetics Education Centre: <a href="https://le.ac.uk/vgec/topics/gene-regulation/gene-regulation-higher-education" target="_blank">Gene Expression and Regulation</a>
|
||
</p>
|
||
<p>National Academies Press: <a href="https://www.nap.edu/read/1859/chapter/6#99" target="_blank">Noncoding DNA—Subtlety, Punctuation, or Just Plain Junk?</a>
|
||
</p>
|
||
<p>Khan Academy: <a href="https://www.khanacademy.org/science/biology/gene-regulation/gene-regulation-in-eukaryotes/a/eukaryotic-transcription-factors" target="_blank">Transcription Factors</a>
|
||
</p>
|
||
<p>The Cell: A Molecular Approach (second edition, 2000): <a href="https://www.ncbi.nlm.nih.gov/books/NBK9904/" target="_blank">Regulation of Transcription in Eukaryotes</a> <span class="desc-text"><img alt="From the National Institutes of Health" class="imgdesc" height="16" src="https://medlineplus.gov/images/nih.png" title="From the National Institutes of Health" width="25"/></span>
|
||
</p>
|
||
<p>Genetic Science Learning Center, University of Utah: <a href="https://learn.genetics.utah.edu/content/basics/centraldogma/" target="_blank">RNA’s Role in the Central Dogma</a>, <a href="https://learn.genetics.utah.edu/content/basics/telomeres/" target="_blank">Telomeres</a>, and <a href="https://learn.genetics.utah.edu/content/basics/readchromosomes/" target="_blank">Centromeres</a>
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</p>
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<section><div class="mp-exp mp-content"><h2>Topics in the Cells and DNA chapter</h2><ul><li><a data-pid="20105" href="https://medlineplus.gov/genetics/understanding/basics/cell/">What is a cell?</a></li><li><a data-pid="20107" href="https://medlineplus.gov/genetics/understanding/basics/dna/">What is DNA?</a></li><li><a data-pid="20109" href="https://medlineplus.gov/genetics/understanding/basics/gene/">What is a gene?</a></li><li><a data-pid="20111" href="https://medlineplus.gov/genetics/understanding/basics/chromosome/">What is a chromosome?</a></li><li><a data-pid="20113" href="https://medlineplus.gov/genetics/understanding/basics/howmanychromosomes/">How many chromosomes do people have?</a></li><li>What is noncoding DNA?</li></ul><p><a data-pid="20081" href="https://medlineplus.gov/genetics/understanding/">Other chapters in Help Me Understand Genetics</a></p></div>
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