A half DNA ladder is a template for copying the whole

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"> <html xmlns="http://www.w3.org/1999/xhtml"> <head> <meta http-equiv="Content-Type" content="text/html; charset=UTF-8" /> <title>A half DNA ladder is a template for copying the whole :: DNA from the Beginning</title> <meta name="description" content="DNA polymerase and an experiment using nitrogen isotopes prove DNA replication." /> <link rel="preload" as="style" src="/css/main.css"> <link rel="preload" as="script" src="/js/swfobject.js"> <link rel="preload" as="script" src="/js/prototype-1.6.1.js"> <link href="/css/main.css" rel="stylesheet" type="text/css" /> <link href='https://fonts.googleapis.com/css?family=Droid+Serif' rel='stylesheet' type='text/css'/> <link href='https://fonts.googleapis.com/css?family=Droid+Sans' rel='stylesheet' type='text/css'/> <script type="text/javascript" src="/js/swfobject.js"></script> <script type="text/javascript" src="/js/prototype-1.6.1.js"></script> </head> <body> <div id="container"> <div id="content"> <div id="header"> <div class="rollover-home"> <a href="/" class="rollover-home" title="DNA from the Beginning Home"><span class="displace">Home</span></a> </div> </div>  <div id="content-container"> <h1><span> Concept 20</span> A half DNA ladder is a template for copying the whole.</h1> <div id="nav"> <ul> <li class="menu1"><a href="index.html" title="CONCEPT" ><span class="displace">CONCEPT</span></a></li> <li class="menu2"><a href="animation.html" title="ANIMATION"><span class="displace">ANIMATION</span></a></li> <li class="menu3"><a href="gallery.html" title="GALLERY"><span class="displace">GALLERY</span></a></li> <li class="menu4"><a href="av.html" title="VIDEO"><span class="displace">VIDEO</span></a></li> <li class="menu5"><a href="bio.html" title="BIO"><span class="displace">BIO</span></a></li> <li class="menu6"><a href="problem.html" title="PROBLEM"><span class="displace">PROBLEM</span></a></li> <li class="menu7"><a href="links.html" title="LINKS" ><span class="displace">LINKS</span></a></li> </ul> <br class="clearfloat" /> </div> <div id="concept"> <img src="/images/20/concept20.jpg" class="concept-image" alt="A half DNA ladder is a template for copying the whole." /> <p>Because of the obligatory pairing of adenine-to-thymine and guanine-to-cytosine, Watson and Crick proposed that one half of the DNA ladder serves as a template for recreating the other half during DNA replication. By 1958, two lines of evidence came together to provide proof of this hypothesis. First, an enzyme was discovered — DNA polymerase — that adds complementary nucleotides to the template provided by a half DNA molecule.</p> <p>Second, an ingenious experiment used nitrogen isotopes to follow the construction of new DNA molecules during successive generations of bacteria. This showed that one strand of each DNA molecule is passed along unchanged to each of two daughter cells. This "conserved" strand acts as the template for DNA polymerase to synthesize a second complementary strand, which completes each new DNA molecule.</p> </div> </div> <br class="clearfloat" /> <div id="footer"> <ul> <li><a href="/">Home</a></li> <li><a href="/sitemap.html">Site Map</a></li> <li><a href="/scientists.html">Scientists</a></li> <li><a href="/glossary.html">Glossary</a></li> <li><a href="/feedback.html">Feedback</a></li> <li><a href="/awards.html">Awards</a></li> <li><a href="/credits.html">Credits</a></li> <li><a href="http://blogs.dnalc.org/dnaftb/" style="background-image:none;">Blog</a></li> </ul> <p> Funded by <a href="http://macyfoundation.org">The Josiah Macy, Jr. Foundation</a><br /> © 2002 - 2011, <a href="http://www.dnalc.org/"> DNA Learning Center</a>, <a href="https://www.cshl.edu/">Cold Spring Harbor Laboratory</a>. All rights reserved. </p> </div>  </div> <div id="sidebar"> <div id="search" > <form method="get" action="/search"> <div class="fieldHolder1"> <input type="search" id="q" name="q" placeholder="Search" onclick="this.value=''" value="" /> <img style="background-color:#9C0;" src="/images/general/search_icon.jpg" alt="Search" onclick="document.forms[0].submit()" /> </div> </form> </div>  <div id="sidebar"> <ul class="menu-side"> <li class="section1" style="margin-bottom: 3px;"><a href="/1/index.html" title="Classical Genetics"><span class="displace">CLASSICAL GENETICS</span></a></li> </ul> <ul class="sections-side sections-side2a" style="padding-top: 56px;"> <li ><a href="/15/"><img src="/images/thumbnails/15-thumb-sm.png" alt="15." />DNA and proteins are key molecules of the cell nucleus.</a></li> <li ><a href="/16/"><img src="/images/thumbnails/16-thumb-sm.png" alt="16." />One gene makes one protein.</a></li> <li ><a href="/17/"><img src="/images/thumbnails/17-thumb-sm.png" alt="17." />A gene is made of DNA.</a></li> <li ><a href="/18/"><img src="/images/thumbnails/18-thumb-sm.png" alt="18." />Bacteria and viruses have DNA too.</a></li> <li ><a href="/19/"><img src="/images/thumbnails/19-thumb-sm.png" alt="19." />The DNA molecule is shaped like a twisted ladder.</a></li> <li ><a class="concept-highlight" href="/20/"><img src="/images/thumbnails/20-thumb-sm.png" alt="20." />A half DNA ladder is a template for copying the whole.</a></li> <li ><a href="/21/"><img src="/images/thumbnails/21-thumb-sm.png" alt="21." />RNA is an intermediary between DNA and protein.</a></li> <li ><a href="/22/"><img src="/images/thumbnails/22-thumb-sm.png" alt="22." />DNA words are three letters long.</a></li> <li ><a href="/23/"><img src="/images/thumbnails/23-thumb-sm.png" alt="23." />A gene is a discrete sequence of DNA nucleotides.</a></li> <li ><a href="/24/"><img src="/images/thumbnails/24-thumb-sm.png" alt="24." />The RNA message is sometimes edited.</a></li> <li ><a href="/25/"><img src="/images/thumbnails/25-thumb-sm.png" alt="25." />Some viruses store genetic information in RNA.</a></li> <li ><a href="/26/"><img src="/images/thumbnails/26-thumb-sm.png" alt="26." />RNA was the first genetic molecule.</a></li> <li ><a href="/27/"><img src="/images/thumbnails/27-thumb-sm.png" alt="27." />Mutations are changes in genetic information.</a></li> <li style="border-bottom: 1px solid #669;"><a href="/28/"><img src="/images/thumbnails/28-thumb-sm.png" alt="28." />Some types of mutations are automatically repaired.</a></li> </ul> <ul class="menu-side"> <li class="section3"><a href="/29/index.html" title="Genetic Organization and Control"><span class="displace">GENETIC ORGANIZATION AND CONTROL</span></a></li> </ul> </div> </div>  <br class="clearfloat" /> </div>  <script type="text/javascript"> Event.observe(window, 'load', function() { var uri = '/20/index.html'; uri = uri.replace(/-\d/,''); $('nav').down().descendants().each(function(s) { if (s.nodeName == 'A') { if (s.href.match(uri)) { s.addClassName('current'); throw $break; } } }); }); </script> <script type="text/javascript"> var _gaq = _gaq || []; _gaq.push(['_setAccount', 'UA-1818773-10']); _gaq.push(['_trackPageview']); (function() { var ga = document.createElement('script'); ga.type = 'text/javascript'; ga.async = true; ga.src = 'https://www.google-analytics.com/ga.js'; var s = document.getElementsByTagName('script')[0]; s.parentNode.insertBefore(ga, s); })(); </script>  <script async src="https://www.googletagmanager.com/gtag/js?id=G-K6EHFCRJBP"></script> <script> window.dataLayer = window.dataLayer || []; function gtag(){dataLayer.push(arguments);} gtag('js', new Date()); gtag('config', 'G-K6EHFCRJBP'); </script> </body> </html>

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A half DNA ladder is a template for copying the whole :: DNA from the Beginning