An Elegant Experiment to Test the Process of DNA Replication | Scientists and Research

<!DOCTYPE html> <html lang="en" dir="ltr"> <head>  <meta http-equiv="X-UA-Compatible" content="ie=edge"> <meta charset="utf-8"> <base href="https://www.visionlearning.com"> <title>An Elegant Experiment to Test the Process of DNA Replication | Scientists and Research | Visionlearning</title> <link rel="canonical" href="https://www.visionlearning.com/en/library/scientists-and-research/58/an-elegant-experiment-to-test-the-process-of-dna-replication/187"> <meta name="description" content="Testing predictions is a major part of scientific research, and a key component of many classic experiments. This module explores the research methods used by Meselson and Stahl in their ingenious 1958 experiment showing how DNA replicates. The module highlights the power of simplicity in what has been called the most beautiful experiment in biology."> <meta name="keywords" content="science, education, STEM, math, biology, chemistry, physics, earth science, online learning"> <meta name="viewport" content="width=device-width, initial-scale=1.0, shrink-to-fit=no"> <meta name="msvalidate.01" content="D8E20F39AD48052260032E56DE409970"> <script type="application/ld+json"> { "@context": "http://schema.org/", "@type": "Article", "mainEntityOfPage": { "@type": "WebPage", "@id": "https://visionlearning.com/en/library/scientists-and-research/58/an-elegant-experiment-to-test-the-process-of-dna-replication/187" }, "name": "An Elegant Experiment to Test the Process of DNA Replication", "headline": "An Elegant Experiment to Test the Process of DNA Replication: The work of Meselsohn and Stahl", "author": { "@type": "Person", "name": "Nathan H Lents, Ph.D." }, "datePublished": "2011-07-27 12:12:27", "dateModified": "2017-02-12T08:30:00+05:00", "image": { "@type": "ImageObject", "url": "/img/library/moduleImages/featured_image_187-23061410064232.jpeg", "width": 696, "height": 464 }, "publisher": { "@type": "Organization", "name": "Visionlearning, Inc.", "logo": { "@type": "ImageObject", "url": "http://visionlearning.com/images/logo.png", "width": 278, "height": 60 } }, "description": "Testing predictions is a major part of scientific research, and a key component of many classic experiments. This module explores the research methods used by Meselson and Stahl in their ingenious 1958 experiment showing how DNA replicates. The module highlights the power of simplicity in what has been called the most beautiful experiment in biology.", "keywords": "science, education, STEM, math, biology, chemistry, physics, earth science, online learning", "inLanguage": { "@type": "Language", "name": "English", "alternateName": "en" }, "copyrightHolder": { "@type": "Organization", "name": "Visionlearning, Inc." }, "copyrightYear": "2011"} </script> <meta property="og:url" content="https://visionlearning.com/en/library/scientists-and-research/58/an-elegant-experiment-to-test-the-process-of-dna-replication/187"> <meta property="og:title" content="An Elegant Experiment to Test the Process of DNA Replication | Scientists and Research | Visionlearning" /> <meta property="og:type" content="website"> <meta property="og:site_name" content="Visionlearning"> <meta property="og:description" content="Testing predictions is a major part of scientific research, and a key component of many classic experiments. This module explores the research methods used by Meselson and Stahl in their ingenious 1958 experiment showing how DNA replicates. 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aria-controls="acc-panel-ecology" aria-expanded="false"> <span class="accordion__button__label"> Ecology </span> </button> <div class="accordion__panel" id="acc-panel-ecology" data-accordion="panel" aria-labelledby="acc-button-ecology" role="region"> <ul class="nav text-color-link"> <li><a href="/en/library/environmental-science/61/biodiversity-i/276">Biodiversity I</a></li> <li><a href="/en/library/environmental-science/61/biodiversity-ii/281">Biodiversity II</a></li> <li><a href="/en/library/environmental-science/61/ecosystem-services/279">Ecosystem Services</a></li> <li><a href="/en/library/environmental-science/61/population-biology/287">Population Biology</a></li> </ul> </div> <button class="accordion__button" id="acc-button-earth-cycles" data-accordion="button" aria-controls="acc-panel-earth-cycles" aria-expanded="false"> <span class="accordion__button__label"> Earth Cycles </span> </button> <div class="accordion__panel" id="acc-panel-earth-cycles" data-accordion="panel" aria-labelledby="acc-button-earth-cycles" role="region"> <ul class="nav text-color-link"> <li><a href="/en/library/environmental-science/61/the-nitrogen-cycle/98">The Nitrogen Cycle</a></li> <li><a href="/en/library/environmental-science/61/the-carbon-cycle/95">The Carbon Cycle</a></li> <li><a href="/en/library/environmental-science/61/the-phosphorus-cycle/197">The Phosphorus Cycle</a></li> </ul> </div> <button class="accordion__button" id="acc-button-scientific-research" data-accordion="button" aria-controls="acc-panel-scientific-research" aria-expanded="false"> <span class="accordion__button__label"> Scientific Research </span> </button> <div class="accordion__panel" id="acc-panel-scientific-research" data-accordion="panel" aria-labelledby="acc-button-scientific-research" role="region"> <ul class="nav text-color-link"> <li><a href="/en/library/environmental-science/61/collaborative-research-in-the-arctic-towards-understanding-climate-change/183">Collaborative Research in the Arctic Towards Understanding Climate Change</a></li> <li><a href="/en/library/environmental-science/61/atmospheric-chemistry-research-that-changed-global-policy/211">Atmospheric Chemistry Research that Changed Global Policy</a></li> </ul> </div> </div> </div> <button class="accordion__button" id="acc-button-general-science" data-accordion="button" aria-controls="acc-panel-general-science" aria-expanded="false"> <span class="accordion__button__label"> General Science </span> </button> <div class="accordion__panel" id="acc-panel-general-science" data-accordion="panel" aria-labelledby="acc-button-general-science" role="region"> <div class="accordion accordion--secondary"> <button class="accordion__button" id="acc-button-methods" data-accordion="button" aria-controls="acc-panel-methods" aria-expanded="false"> <span class="accordion__button__label"> Methods </span> </button> <div class="accordion__panel" id="acc-panel-methods" data-accordion="panel" aria-labelledby="acc-button-methods" role="region"> <ul class="nav text-color-link"> <li><a href="/en/library/general-science/3/the-scientific-method/45">The Scientific Method</a></li> </ul> </div> <button class="accordion__button" id="acc-button-measurement" data-accordion="button" aria-controls="acc-panel-measurement" aria-expanded="false"> <span class="accordion__button__label"> Measurement </span> </button> <div class="accordion__panel" id="acc-panel-measurement" data-accordion="panel" aria-labelledby="acc-button-measurement" role="region"> <ul class="nav text-color-link"> <li><a href="/en/library/general-science/3/the-metric-system/47">The Metric System</a></li> </ul> </div> <button class="accordion__button" id="acc-button-physical-properties" data-accordion="button" aria-controls="acc-panel-physical-properties" aria-expanded="false"> <span class="accordion__button__label"> Physical Properties </span> </button> <div class="accordion__panel" id="acc-panel-physical-properties" data-accordion="panel" aria-labelledby="acc-button-physical-properties" role="region"> <ul class="nav text-color-link"> <li><a href="/en/library/general-science/3/temperature/48">Temperature</a></li> <li><a href="/en/library/general-science/3/density-and-buoyancy/37">Density and Buoyancy</a></li> </ul> </div> </div> </div> <button class="accordion__button" id="acc-button-math-in-science" data-accordion="button" aria-controls="acc-panel-math-in-science" aria-expanded="false"> <span class="accordion__button__label"> Math in Science </span> </button> <div class="accordion__panel" id="acc-panel-math-in-science" data-accordion="panel" aria-labelledby="acc-button-math-in-science" role="region"> <div class="accordion accordion--secondary"> <button class="accordion__button" id="acc-button-equations" data-accordion="button" aria-controls="acc-panel-equations" aria-expanded="false"> <span class="accordion__button__label"> Equations </span> </button> <div class="accordion__panel" id="acc-panel-equations" data-accordion="panel" aria-labelledby="acc-button-equations" role="region"> <ul class="nav text-color-link"> <li><a href="/en/library/math-in-science/62/unit-conversion/144">Unit Conversion</a></li> <li><a href="/en/library/math-in-science/62/linear-equations/194">Linear Equations</a></li> <li><a href="/en/library/math-in-science/62/exponential-equations-i/206">Exponential Equations I</a></li> <li><a href="/en/library/math-in-science/62/exponential-equations-ii/210">Exponential Equations II</a></li> <li><a href="/en/library/math-in-science/62/scientific-notation/250">Scientific Notation</a></li> <li><a href="/en/library/math-in-science/62/measurement/257">Measurement</a></li> </ul> </div> <button class="accordion__button" id="acc-button-statistics" data-accordion="button" aria-controls="acc-panel-statistics" aria-expanded="false"> <span class="accordion__button__label"> Statistics </span> </button> <div class="accordion__panel" id="acc-panel-statistics" data-accordion="panel" aria-labelledby="acc-button-statistics" role="region"> <ul class="nav text-color-link"> <li><a href="/en/library/math-in-science/62/introduction-to-descriptive-statistics/218">Introduction to Descriptive Statistics</a></li> <li><a href="/en/library/math-in-science/62/introduction-to-inferential-statistics/224">Introduction to Inferential Statistics</a></li> <li><a href="/en/library/math-in-science/62/statistical-techniques/239">Statistical Techniques</a></li> </ul> </div> <button class="accordion__button" id="acc-button-trigonometric-functions" data-accordion="button" aria-controls="acc-panel-trigonometric-functions" aria-expanded="false"> <span class="accordion__button__label"> Trigonometric Functions </span> </button> <div class="accordion__panel" id="acc-panel-trigonometric-functions" data-accordion="panel" aria-labelledby="acc-button-trigonometric-functions" role="region"> <ul class="nav text-color-link"> <li><a href="/en/library/math-in-science/62/wave-mathematics/131">Wave Mathematics</a></li> </ul> </div> </div> </div> <button class="accordion__button" id="acc-button-physics" data-accordion="button" aria-controls="acc-panel-physics" aria-expanded="false"> <span class="accordion__button__label"> Physics </span> </button> <div class="accordion__panel" id="acc-panel-physics" data-accordion="panel" aria-labelledby="acc-button-physics" role="region"> <div class="accordion accordion--secondary"> <button class="accordion__button" id="acc-button-light-and-optics" data-accordion="button" aria-controls="acc-panel-light-and-optics" aria-expanded="false"> <span class="accordion__button__label"> Light and Optics </span> </button> <div class="accordion__panel" id="acc-panel-light-and-optics" data-accordion="panel" aria-labelledby="acc-button-light-and-optics" role="region"> <ul class="nav text-color-link"> <li><a href="/en/library/physics/24/the-nature-of-light/132">The Nature of Light</a></li> <li><a href="/en/library/physics/24/electromagnetism-and-light/138">Electromagnetism and Light</a></li> </ul> </div> <button class="accordion__button" id="acc-button-mechanics" data-accordion="button" aria-controls="acc-panel-mechanics" aria-expanded="false"> <span class="accordion__button__label"> Mechanics </span> </button> <div class="accordion__panel" id="acc-panel-mechanics" data-accordion="panel" aria-labelledby="acc-button-mechanics" role="region"> <ul class="nav text-color-link"> <li><a href="/en/library/physics/24/defining-energy/199">Defining Energy</a></li> <li><a href="/en/library/physics/24/waves-and-wave-motion/102">Waves and Wave Motion</a></li> <li><a href="/en/library/physics/24/gravity/118">Gravity</a></li> <li><a href="/en/library/physics/24/thermodynamics-i/200">Thermodynamics I</a></li> </ul> </div> </div> </div> <button class="accordion__button" id="acc-button-process-of-science" data-accordion="button" aria-controls="acc-panel-process-of-science" aria-expanded="false"> <span class="accordion__button__label"> Process of Science </span> </button> <div class="accordion__panel" id="acc-panel-process-of-science" data-accordion="panel" aria-labelledby="acc-button-process-of-science" role="region"> <div class="accordion accordion--secondary"> <button class="accordion__button" id="acc-button-introduction" data-accordion="button" aria-controls="acc-panel-introduction" aria-expanded="false"> <span class="accordion__button__label"> Introduction </span> </button> <div class="accordion__panel" id="acc-panel-introduction" data-accordion="panel" aria-labelledby="acc-button-introduction" role="region"> <ul class="nav text-color-link"> <li><a href="/en/library/process-of-science/49/the-process-of-science/176">The Process of Science</a></li> </ul> </div> <button class="accordion__button" id="acc-button-the-culture-of-science" data-accordion="button" aria-controls="acc-panel-the-culture-of-science" aria-expanded="false"> <span class="accordion__button__label"> The Culture of Science </span> </button> <div class="accordion__panel" id="acc-panel-the-culture-of-science" data-accordion="panel" aria-labelledby="acc-button-the-culture-of-science" role="region"> <ul class="nav text-color-link"> <li><a href="/en/library/process-of-science/49/the-nature-of-scientific-knowledge/185">The Nature of Scientific Knowledge</a></li> <li><a href="/en/library/process-of-science/49/scientists-and-the-scientific-community/172">Scientists and the Scientific Community</a></li> <li><a href="/en/library/process-of-science/49/scientific-ethics/161">Scientific Ethics</a></li> <li><a href="/en/library/process-of-science/49/scientific-institutions-and-societies/162">Scientific Institutions and Societies</a></li> </ul> </div> <button class="accordion__button" id="acc-button-ideas-in-science" data-accordion="button" aria-controls="acc-panel-ideas-in-science" aria-expanded="false"> <span class="accordion__button__label"> Ideas in Science </span> </button> <div class="accordion__panel" id="acc-panel-ideas-in-science" data-accordion="panel" aria-labelledby="acc-button-ideas-in-science" role="region"> <ul class="nav text-color-link"> <li><a href="/en/library/process-of-science/49/theories-hypotheses-and-laws/177">Theories, Hypotheses, and Laws</a></li> <li><a href="/en/library/process-of-science/49/scientific-controversy/181">Scientific Controversy</a></li> <li><a href="/en/library/process-of-science/49/creativity-in-science/182">Creativity in Science</a></li> </ul> </div> <button class="accordion__button" id="acc-button-research-methods" data-accordion="button" aria-controls="acc-panel-research-methods" aria-expanded="false"> <span class="accordion__button__label"> Research Methods </span> </button> <div class="accordion__panel" id="acc-panel-research-methods" data-accordion="panel" aria-labelledby="acc-button-research-methods" role="region"> <ul class="nav text-color-link"> <li><a href="/en/library/process-of-science/49/the-practice-of-science/148">The Practice of Science</a></li> <li><a href="/en/library/process-of-science/49/experimentation-in-scientific-research/150">Experimentation in Scientific Research</a></li> <li><a href="/en/library/process-of-science/49/description-in-scientific-research/151">Description in Scientific Research</a></li> <li><a href="/en/library/process-of-science/49/comparison-in-scientific-research/152">Comparison in Scientific Research</a></li> <li><a href="/en/library/process-of-science/49/modeling-in-scientific-research/153">Modeling in Scientific Research</a></li> </ul> </div> <button class="accordion__button" id="acc-button-data" data-accordion="button" aria-controls="acc-panel-data" aria-expanded="false"> <span class="accordion__button__label"> Data </span> </button> <div class="accordion__panel" id="acc-panel-data" data-accordion="panel" aria-labelledby="acc-button-data" role="region"> <ul class="nav text-color-link"> <li><a href="/en/library/process-of-science/49/data-analysis-and-interpretation/154">Data Analysis and Interpretation</a></li> <li><a href="/en/library/process-of-science/49/uncertainty-error-and-confidence/157">Uncertainty, Error, and Confidence</a></li> <li><a href="/en/library/process-of-science/49/statistics-in-science/155">Statistics in Science</a></li> <li><a href="/en/library/process-of-science/49/using-graphs-and-visual-data-in-science/156">Using Graphs and Visual Data in Science</a></li> </ul> </div> <button class="accordion__button" id="acc-button-scientific-communication" data-accordion="button" aria-controls="acc-panel-scientific-communication" aria-expanded="false"> <span class="accordion__button__label"> Scientific Communication </span> </button> <div class="accordion__panel" id="acc-panel-scientific-communication" data-accordion="panel" aria-labelledby="acc-button-scientific-communication" role="region"> <ul class="nav text-color-link"> <li><a href="/en/library/process-of-science/49/understanding-scientific-journals-and-articles/158">Understanding Scientific Journals and Articles</a></li> <li><a href="/en/library/process-of-science/49/utilizing-the-scientific-literature/173">Utilizing the Scientific Literature</a></li> <li><a href="/en/library/process-of-science/49/peer-review-in-scientific-publishing/159">Peer Review in Scientific Publishing</a></li> <li><a href="/en/library/process-of-science/49/the-how-and-why-of-scientific-meetings/186">The How and Why of Scientific Meetings</a></li> </ul> </div> </div> </div> <button class="accordion__button" id="acc-button-scientists-and-research" data-accordion="button" aria-controls="acc-panel-scientists-and-research" aria-expanded="false"> <span class="accordion__button__label"> Scientists and Research </span> </button> <div class="accordion__panel" id="acc-panel-scientists-and-research" data-accordion="panel" aria-labelledby="acc-button-scientists-and-research" role="region"> <div class="accordion accordion--secondary"> <button class="accordion__button" id="acc-button-scientific-research" data-accordion="button" aria-controls="acc-panel-scientific-research" aria-expanded="false"> <span class="accordion__button__label"> Scientific Research </span> </button> <div class="accordion__panel" id="acc-panel-scientific-research" data-accordion="panel" aria-labelledby="acc-button-scientific-research" role="region"> <ul class="nav text-color-link"> <li><a href="/en/library/scientists-and-research/58/collaborative-research-in-the-arctic-towards-understanding-climate-change/183">Collaborative Research in the Arctic Towards Understanding Climate Change</a></li> <li><a href="/en/library/scientists-and-research/58/from-stable-chromosomes-to-jumping-genes/184">From Stable Chromosomes to Jumping Genes</a></li> <li class="current">An Elegant Experiment to Test the Process of DNA Replication</li> <li><a href="/en/library/scientists-and-research/58/the-founding-of-neuroscience/233">The Founding of Neuroscience</a></li> <li><a href="/en/library/scientists-and-research/58/tracking-endangered-jaguars-across-the-border/189">Tracking Endangered Jaguars across the Border</a></li> <li><a href="/en/library/scientists-and-research/58/atmospheric-chemistry-research-that-changed-global-policy/211">Atmospheric Chemistry Research that Changed Global Policy</a></li> <li><a href="/en/library/scientists-and-research/58/revolutionizing-medicine-with-monoclonal-antibodies/220">Revolutionizing Medicine with Monoclonal Antibodies</a></li> <li><a href="/en/library/scientists-and-research/58/uncovering-the-mysteries-of-chronic-mountain-sickness/238">Uncovering the Mysteries of Chronic Mountain Sickness</a></li> </ul> </div> <button class="accordion__button" id="acc-button-profiles-in-science" data-accordion="button" aria-controls="acc-panel-profiles-in-science" aria-expanded="false"> <span class="accordion__button__label"> Profiles in Science </span> </button> <div class="accordion__panel" id="acc-panel-profiles-in-science" data-accordion="panel" aria-labelledby="acc-button-profiles-in-science" role="region"> <ul class="nav text-color-link"> <li><a href="/en/library/scientists-and-research/58/luis-e.-miramontes/232">Luis E. Miramontes</a></li> <li><a href="/en/library/scientists-and-research/58/bernardo-houssay/237">Bernardo Houssay</a></li> <li><a href="/en/library/scientists-and-research/58/craig-lee/256">Craig Lee</a></li> <li><a href="/en/library/scientists-and-research/58/david-ho/241">David Ho</a></li> <li><a href="/en/library/scientists-and-research/58/louis-tompkins-wright/244">Louis Tompkins Wright</a></li> <li><a href="/en/library/scientists-and-research/58/carlos-j.-finlay/217">Carlos J. Finlay</a></li> <li><a href="/en/library/scientists-and-research/58/cecilia-payne/290">Cecilia Payne</a></li> <li><a href="/en/library/scientists-and-research/58/jazmin-scarlett/291">Jazmin Scarlett</a></li> <li><a href="/en/library/scientists-and-research/58/ramari-stewart/292">Ramari Stewart</a></li> <li><a href="/en/library/scientists-and-research/58/johnson-cerda/300">Johnson Cerda</a></li> <li><a href="/en/library/scientists-and-research/58/ellen-ochoa/201">Ellen Ochoa</a></li> <li><a href="/en/library/scientists-and-research/58/ruth-benerito/205">Ruth Benerito</a></li> <li><a href="/en/library/scientists-and-research/58/franklin-chang-d铆az/219">Franklin Chang D铆az</a></li> <li><a href="/en/library/scientists-and-research/58/percy-lavon-julian/221">Percy Lavon Julian</a></li> <li><a href="/en/library/scientists-and-research/58/luis-walter-alvarez/229">Luis Walter Alvarez</a></li> <li><a href="/en/library/scientists-and-research/58/france-anne-dominic-c贸rdova/230">France Anne-Dominic C贸rdova</a></li> </ul> </div> </div> </div> </div> </div> </li> <li>  <button class="button" data-toggle="dropdown">Scientists and Research </button> <div class="nav__dropdown box-shadow-1 padding-1"> <div class="accordion accordion--secondary font-size-sm"> <div class="accordion accordion--secondary"> <button class="accordion__button" id="acc-sub-button-scientific-research" data-accordion="button" aria-controls="acc-sub-panel-scientific-research" aria-expanded="false"> <span class="accordion__button__label"> Scientific Research </span> </button> <div class="accordion__panel" id="acc-sub-panel-scientific-research" data-accordion="panel" aria-labelledby="acc-sub-button-scientific-research" role="region"> <ul class="nav text-color-link"> <li><a href="/en/library/scientists-and-research/58/collaborative-research-in-the-arctic-towards-understanding-climate-change/183">Collaborative Research in the Arctic Towards Understanding Climate Change</a></li> <li><a href="/en/library/scientists-and-research/58/from-stable-chromosomes-to-jumping-genes/184">From Stable Chromosomes to Jumping Genes</a></li> <li class="current">An Elegant Experiment to Test the Process of DNA Replication</li> <li><a href="/en/library/scientists-and-research/58/the-founding-of-neuroscience/233">The Founding of Neuroscience</a></li> <li><a href="/en/library/scientists-and-research/58/tracking-endangered-jaguars-across-the-border/189">Tracking Endangered Jaguars across the Border</a></li> <li><a href="/en/library/scientists-and-research/58/atmospheric-chemistry-research-that-changed-global-policy/211">Atmospheric Chemistry Research that Changed Global Policy</a></li> <li><a href="/en/library/scientists-and-research/58/revolutionizing-medicine-with-monoclonal-antibodies/220">Revolutionizing Medicine with Monoclonal Antibodies</a></li> <li><a href="/en/library/scientists-and-research/58/uncovering-the-mysteries-of-chronic-mountain-sickness/238">Uncovering the Mysteries of Chronic Mountain Sickness</a></li> </ul> </div> <button class="accordion__button" id="acc-sub-button-profiles-in-science" data-accordion="button" aria-controls="acc-sub-panel-profiles-in-science" aria-expanded="false"> <span class="accordion__button__label"> Profiles in Science </span> </button> <div class="accordion__panel" id="acc-sub-panel-profiles-in-science" data-accordion="panel" aria-labelledby="acc-sub-button-profiles-in-science" role="region"> <ul class="nav text-color-link"> <li><a href="/en/library/scientists-and-research/58/luis-e.-miramontes/232">Luis E. Miramontes</a></li> <li><a href="/en/library/scientists-and-research/58/bernardo-houssay/237">Bernardo Houssay</a></li> <li><a href="/en/library/scientists-and-research/58/craig-lee/256">Craig Lee</a></li> <li><a href="/en/library/scientists-and-research/58/david-ho/241">David Ho</a></li> <li><a href="/en/library/scientists-and-research/58/louis-tompkins-wright/244">Louis Tompkins Wright</a></li> <li><a href="/en/library/scientists-and-research/58/carlos-j.-finlay/217">Carlos J. Finlay</a></li> <li><a href="/en/library/scientists-and-research/58/cecilia-payne/290">Cecilia Payne</a></li> <li><a href="/en/library/scientists-and-research/58/jazmin-scarlett/291">Jazmin Scarlett</a></li> <li><a href="/en/library/scientists-and-research/58/ramari-stewart/292">Ramari Stewart</a></li> <li><a href="/en/library/scientists-and-research/58/johnson-cerda/300">Johnson Cerda</a></li> <li><a href="/en/library/scientists-and-research/58/ellen-ochoa/201">Ellen Ochoa</a></li> <li><a href="/en/library/scientists-and-research/58/ruth-benerito/205">Ruth Benerito</a></li> <li><a href="/en/library/scientists-and-research/58/franklin-chang-d铆az/219">Franklin Chang D铆az</a></li> <li><a href="/en/library/scientists-and-research/58/percy-lavon-julian/221">Percy Lavon Julian</a></li> <li><a href="/en/library/scientists-and-research/58/luis-walter-alvarez/229">Luis Walter Alvarez</a></li> <li><a href="/en/library/scientists-and-research/58/france-anne-dominic-c贸rdova/230">France Anne-Dominic C贸rdova</a></li> </ul> </div> </div> </div> </div> </li> </ul> </nav>  <div id="theTop"></div> <main id="skip-header-content"> <div class="margin-bottom-5"> <div class="container narrow wide--lg margin-y-4"> <article class="module"> <header class="module__header"> <span class="subcategory"> <strong><em>Scientific Research</em></strong> </span> <h1>An Elegant Experiment to Test the Process of DNA Replication: <sub><em>The work of Meselsohn and Stahl</em></sub></h1> <p class="byline">by Nathan H Lents, Ph.D.</p> </header> <nav class="module__tabs"> <ul class="tabs-nav tabs-nav--pill tabs-nav--horizontal--md library"> <li> <a href="/en/library/scientists-and-research/58/an-elegant-experiment-to-test-the-process-of-dna-replication/187/reading" class="is-active" aria-current="page" >Reading</a> </li> <li> <a href="/en/library/scientists-and-research/58/an-elegant-experiment-to-test-the-process-of-dna-replication/187/quiz" >Quiz</a> </li> <li> <a href="/en/library/scientists-and-research/58/an-elegant-experiment-to-test-the-process-of-dna-replication/187/resources" >Teach with this</a> </li> </ul> </nav> <hr class="module__divider" />  <div class="module__tools"> <aside class="module__tools__container border-radius box-shadow-1"> <div class="tabs tabs--toggle-mobile--lg" role="tablist"> <ul class="tab__buttons"> <li> <button class="button button--icon-over-text" aria-label="In this module" aria-controls="tab-panel-module__tools" aria-selected="true" role="tab"> <span class="button__icon"> <span class="icon icon-list" aria-hidden="true"></span> </span> <span class="button__text">Contents</span> </button> </li> <li> <button class="button button--icon-over-text" aria-controls="tab-panel-toggle-terms" aria-selected="false" role="tab"> <span class="button__icon"> <span class="icon icon-glossary-highlight"></span> </span> <span class="button__text">Glossary Terms</span> </button> </li> </ul> <div class="tabs__panel shown" id="tab-panel-module__tools" aria-labelledby="tab-button-module__tools" role="tabpanel"> <div class="table-of-contents"> <p class="table-of-contents__title"> Table of Contents </p> <ul class="table-of-contents__nav"> <li><a href="/en/library/scientists-and-research/58/an-elegant-experiment-to-test-the-process-of-dna-replication/187#toc_1">DNA replication</a> </li> <li><a href="/en/library/scientists-and-research/58/an-elegant-experiment-to-test-the-process-of-dna-replication/187#toc_2">Design of the Meselson and Stahl experiment</a> </li> <li><a href="/en/library/scientists-and-research/58/an-elegant-experiment-to-test-the-process-of-dna-replication/187#toc_3">How the experiment tested all three DNA replication hypotheses</a> </li> <li><a href="/en/library/scientists-and-research/58/an-elegant-experiment-to-test-the-process-of-dna-replication/187#toc_4">"The most beautiful experiment in biology"</a> </li> </ul> </div> </div> <div class="tabs__panel" id="tab-panel-toggle-terms" aria-labelledby="tab-button-toggle-terms" role="tabpanel"> <div class="reading-toggle"> <div class="reading-toggle__switch"> <div class="form-entry__option__switch"> <label> <input type="checkbox" name="termsToggleSwitch" id="terms-toggle-switch" /> <span class="switch__slider"></span> <span class="option__label text-decoration-none font-size-md"> Highlight Glossary Terms </span> </label> </div> </div> <div class="reading-toggle__help"> <p> <em> Activate glossary term highlighting to easily identify key terms within the module. Once highlighted, you can click on these terms to view their definitions. </em> </p> </div> </div> <div class="glossary-container"></div> </div> <div class="tabs__panel" id="tab-panel-toggle-ngss" aria-labelledby="tab-button-toggle-ngss" role="tabpanel"> <div class="reading-toggle"> <div class="reading-toggle__switch"> <div class="form-entry__option__switch"> <label> <input type="checkbox" name="ngssToggleSwitch" id="ngss-toggle-switch" /> <span class="switch__slider"></span> <span class="option__label text-decoration-none font-size-md"> Show NGSS Annotations </span> </label> </div> </div> <div class="reading-toggle__help"> <p> <em> Activate NGSS annotations to easily identify NGSS standards within the module. Once highlighted, you can click on them to view these standards. </em> </p> </div> </div> <div class="ngss-container"></div> </div> </div> </aside> <div class="margin-3"> <script async src="https://pagead2.googlesyndication.com/pagead/js/adsbygoogle.js?client=ca-pub-9561344156007092" crossorigin="anonymous"></script>  <ins class="adsbygoogle" style="display:block" data-ad-client="ca-pub-9561344156007092" data-ad-slot="7634263342" data-ad-format="auto" data-full-width-responsive="true"></ins> <script> (adsbygoogle = window.adsbygoogle || []).push({}); </script> </div> </div>     <div class="module__main"> <div class="module__main__container"> <div class="accordion">  <button class="accordion__button" id="acc-button-key-concepts" data-accordion="button" aria-controls="acc-panel-key-concepts" aria-expanded="true" tabindex="0"> Did you know? </button> <div class="accordion__panel shown show" id="acc-panel-key-concepts" data-accordion="panel" aria-labelledby="acc-button-key-concepts" role="region"> <div class="accordion__panel__content"> <p>Did you know that many classic experiments in science are famous not because of their complexity but because of their simplicity? This is the case with Meselson and Stahl鈥檚 classic experiment in DNA replication. In one of the most famous experiments in molecular biology, Meselson and Stahl elegantly tested three scientific hypotheses with one simple design.</p> </div> </div>  <button class="accordion__button" id="acc-button-terms-you-should-know" data-accordion="button" aria-controls="acc-panel-terms-you-should-know" aria-expanded="false" tabindex="0"> Terms you should know </button> <div class="accordion__panel" id="acc-panel-terms-you-should-know" data-accordion="panel" aria-labelledby="acc-button-terms-you-should-know" role="region" aria-hidden="true"> <div class="accordion__panel__content"> <dl> <dt>centrifuge </dt> <dd> an instrument that uses rotating force to separate particles according to density </dd> <dt><a href="/en/glossary/view/experiment">experiment </a></dt> <dd> a test or trial carried out under controlled conditions so that specific actions can be performed and the results can be observed </dd> <dt><a href="/en/glossary/view/model">model </a></dt> <dd> a representation or mathematical description of a system </dd> <dt><a href="/en/glossary/view/replication">replication </a></dt> <dd> the process of making an exact copy</dd> </dl> </div> </div> </div> <section> <p>Around the world, there are thousands of scientists performing <mark class="term" data-term="experiment" data-term-def="A test or trial carried out under controlled conditions so that specific actions can be performed and the results can be observed." data-term-url="/en/glossary/view/experiment/8292">experiments</mark> at any given moment. Every once in a while, an experiment is performed and published that appears so clever, so important, and so successful in its goals, that it is destined to be cheered by scientists far and wide and taught in science classrooms for decades to come. However, with the passage of time, these so-called "classic experiments" seem more dramatic, ingenious, and clear than they were in their contemporary timing as the memories of complications, contradictions, and <mark class="term" data-term="controversy" data-term-def="An argument, disagreement, or difference of opinion that involves many people. A true scientific controversy involves a sustained debate within the&hellip;" data-term-url="/en/glossary/view/controversy/8241">controversy</mark> fade. Nevertheless, what often sets apart these key experiments is not that they are especially complex, but that they are elegantly simple. The power of simplicity in an experiment is that it reduces the chance of alternative explanations for the results. </p> <p>As explained in our module <a href="http://www.visionlearning.com/library/module_viewer.php?mid=177&l=">Theories <mark class="term" data-term="hypothesis" data-term-url="/en/glossary/view/hypothesis" data-term-def="From the Greek word <em>hypothesis</em> meaning assumption or the basis of an argument, a hypothesis is a proposal intended to explain&hellip;">Hypotheses</mark>, and Laws</a>, a key feature of the modern scientific <mark class="term" data-term="method" data-term-def="A procedure or process; a systematic way of performing a task or conducting research." data-term-url="/en/glossary/view/method/8238">method</mark> is that valid scientific hypotheses make predictions that can be tested. Thus, the testing of predictions is a major part of scientific <mark class="term" data-term="research" data-term-def="A study or an investigation." data-term-url="/en/glossary/view/research/8257">research</mark>, and part of the historic nature of many classic <mark class="term" data-term="experiment" data-term-def="A test or trial carried out under controlled conditions so that specific actions can be performed and the results can be observed." data-term-url="/en/glossary/view/experiment/8292">experiments</mark> is that they tested the predictions of a key scientific <mark class="term" data-term="hypothesis" data-term-def="From the Greek word <em>hypothesis</em> meaning assumption or the basis of an argument, a hypothesis is a proposal intended to explain&hellip;" data-term-url="/en/glossary/view/hypothesis/3727">hypothesis</mark> in a way that provided a clear answer. The 1958 experiment by Matthew Meselson and Franklin Stahl is an example of such an experiment, and is one of the most famous in all of molecular biology. With one cleverly designed experiment, they tested the predictions of three different scientific hypotheses simultaneously, and the field of <mark class="term" data-term="DNA" data-term-def="Deoxyribonucleic acid. A double-stranded nucleic acid containing the sugar 2-deoxy-D-ribose. A constituent of cellular nuclear material responsible for encoding&hellip;" data-term-url="/en/glossary/view/DNA/1604">DNA</mark> biology was changed forever.</p> <p><section id="toc_1" class=""> <h2>DNA replication</h2></p> <p>Following the discovery of <mark class="term" data-term="DNA" data-term-def="Deoxyribonucleic acid. A double-stranded nucleic acid containing the sugar 2-deoxy-D-ribose. A constituent of cellular nuclear material responsible for encoding&hellip;" data-term-url="/en/glossary/view/DNA/1604">DNA</mark> as the genetic material (see <a href="http://www.visionlearning.com/library/module_viewer.php?mid=149&l=">DNA I</a>), the new field of molecular biology focused intently on how DNA functions. One of the most important features of DNA is its ability to be copied accurately. When a <mark class="term" data-term="cell" data-term-def="The basic structural unit of all living things." data-term-url="/en/glossary/view/cell/8286">cell</mark>, whether it is a <mark class="term" data-term="yeast" data-term-def="Eukaryotic, single-celled organisms belonging to the fungi kingdom." data-term-url="/en/glossary/view/yeast/10190">yeast</mark>, a bacterium, or a human cell, divides in two, both resulting cells are genetically identical to each other and to the original <mark class="term" data-term="parent" data-term-def="The material or source from which something is derived." data-term-url="/en/glossary/view/parent/1618">parent</mark> cell. Thus, prior to division, a cell must somehow copy all of its DNA so that both resulting cells have the full complement of genetic material. Indeed, scientists such as Edwin Chargaff and others had observed that the amount of DNA in a cell doubles prior to cell division. The pool of DNA is then split equally between the two <mark class="term" data-term="daughter" data-term-def="A material that is derived from the breakdown or division of another. For example, a product of the radioactive decay of&hellip;" data-term-url="/en/glossary/view/daughter/10177">daughter</mark> cells, so that both have the same amount of DNA as the original parent cell had. But how exactly this DNA doubling takes place was at first a mystery, and scientists began to propose several possible mechanisms, or "models" of DNA replication?</p><p>Following the proposal and eventual acceptance of the Watson-Crick <mark class="term" data-term="model" data-term-def="A representation, pattern, or mathematical description that can help scientists replicate a system." data-term-url="/en/glossary/view/model/8236">model</mark> of <mark class="term" data-term="DNA" data-term-def="Deoxyribonucleic acid. A double-stranded nucleic acid containing the sugar 2-deoxy-D-ribose. A constituent of cellular nuclear material responsible for encoding&hellip;" data-term-url="/en/glossary/view/DNA/1604">DNA</mark> structure, molecular biologists believed that each strand of DNA somehow served as a copy-template for the <mark class="term" data-term="synthesis" data-term-def="The production of a chemical compound by combining simpler compounds or elements." data-term-url="/en/glossary/view/synthesis/8756">synthesis</mark> of a new DNA <mark class="term" data-term="molecule" data-term-def="A particle formed by the chemical bonding of two or more atoms. The molecule is the smallest particle of a&hellip;" data-term-url="/en/glossary/view/molecule/1518">molecule</mark> (see our <a href="http://www.visionlearning.com/library/module_viewer.php?mid=160&l=">DNA II</a> module for more information). However, conundrums remained. Most importantly, scientists had a difficult time envisioning how two strands of DNA that are immensely long and twisted around each other could separate from each other without resulting in the breakage of the strands or them becoming hopelessly entangled. In addition, scientists wondered how the two strands could be pulled apart given the enormous number of hydrogen <mark class="term" data-term="bond" data-term-def="The force that holds together units such as atoms or molecules. <br> <b>[verb]</b> To hold or fasten units such as atoms or molecules together." data-term-url="/en/glossary/view/bond/8297">bonds</mark> holding them together. Some envisioned replication as proceeding in short stretches, while others imagined a continuous <mark class="term" data-term="process" data-term-def="Method, procedure; series of actions or steps." data-term-url="/en/glossary/view/process/8256">process</mark> much like a zipper. This paradox even caused some prominent scientists of the day to doubt the double-helix structure of DNA altogether. Nevertheless, scientists began working on possible theoretical solutions to the separation of two intertwined DNA strands and by the late 1950s, three hypothetical models for DNA synthesis were being hotly debated: the conservative model, the semi-conservative model, and the dispersive model. Figure 1 below provides a diagram of each of these mechanisms.</p> <div class="container margin-y-4 text-align-center"> <script async src="https://pagead2.googlesyndication.com/pagead/js/adsbygoogle.js?client=ca-pub-9561344156007092" crossorigin="anonymous"></script>  <ins class="adsbygoogle" style="display:inline-block;width:300px;height:250px" data-ad-client="ca-pub-9561344156007092" data-ad-slot="9090201191"></ins> <script> (adsbygoogle = window.adsbygoogle || []).push({}); </script> </div>  <div class="figure"> <figure> <button class="lightbox-button" data-lightbox-src="/img/library/large_images/image_5555.jpg" data-lightbox="image"> <img src="/img/library/modules/mid187/Image/VLObject-5555-110727100704.jpg" alt="Figure 1: Three competing models of DNA replication. This diagram shows the three competing models of DNA replication in the 1950s and 1960s." /> </button> <figcaption> <p><b><strong>Figure 1:</strong> Three competing models of DNA replication.</b> This diagram shows the three competing models of DNA replication in the 1950s and 1960s.</p> <span class="credit">image ©N. Lents</span> </figcaption> </figure> </div> <p>Briefly stated, the conservative <mark class="term" data-term="model" data-term-def="A representation, pattern, or mathematical description that can help scientists replicate a system." data-term-url="/en/glossary/view/model/8236">model</mark> of <mark class="term" data-term="DNA" data-term-def="Deoxyribonucleic acid. A double-stranded nucleic acid containing the sugar 2-deoxy-D-ribose. A constituent of cellular nuclear material responsible for encoding&hellip;" data-term-url="/en/glossary/view/DNA/1604">DNA</mark> <mark class="term" data-term="replication" data-term-def="In science, quality research studies are designed such that the exact procedures and methods followed by the scientists are clear and&hellip;" data-term-url="/en/glossary/view/replication/3730">replication</mark> holds that when DNA is replicated prior to <mark class="term" data-term="cell" data-term-def="The basic structural unit of all living things." data-term-url="/en/glossary/view/cell/8286">cell</mark> division, one of the DNA double-strands receives all newly replicated DNA in both strands, while the other receives only the two original DNA strands in the <mark class="term" data-term="parent" data-term-def="The material or source from which something is derived." data-term-url="/en/glossary/view/parent/1618">parent</mark> cell. The semi-conservative model (also called the "zipper model" by James Watson), however, holds that the original two strands of DNA are split from each other and that the two <mark class="term" data-term="daughter" data-term-def="A material that is derived from the breakdown or division of another. For example, a product of the radioactive decay of&hellip;" data-term-url="/en/glossary/view/daughter/10177">daughter</mark> <mark class="term" data-term="molecule" data-term-def="A particle formed by the chemical bonding of two or more atoms. The molecule is the smallest particle of a&hellip;" data-term-url="/en/glossary/view/molecule/1518">molecules</mark> are each comprised of one "old" strand of DNA from the parent cell, and one newly replicated strand. Finally, the dispersive model holds that the DNA is copied in short stretches and that both daughter DNA strands will receive a mixture of the original parental DNA and newly replicated DNA. Each of these three possible models had been proposed by different scientists and each had certain advantages in explaining the separation of the intertwined parental DNA. However, <mark class="term" data-term="evidence" data-term-def="Support for an idea, opinion, or hypothesis." data-term-url="/en/glossary/view/evidence/8243">evidence</mark> to disprove or support any of the models was scarce.</p> <div class="comprehension-checkpoint margin-y-4"> <h6 class="comprehension-checkpoint__header"> <span> <span class="icon icon-question"></span> </span> Comprehension Checkpoint </h6> <form name="cc6504"> <div class="form-entry"> <div class="form-entry__field"> <span class="form-entry__field__label">In the 1950s, scientists were not sure</span> <div class="form-entry__option"> <div class="form-entry__option__radio" data-answer="incorrect"> <label> <input id="q1-6504-0-option-a" name="quiz-option-6504" type="radio" value="whether DNA replicated." > <span class="option__label"> <span class="screen-reader-only">a.</span> whether DNA replicated. </span> </label> <span class="quiz__response" id="response-6504-0"> <strong>Incorrect.</strong> </span> </div> <div class="form-entry__option__radio" data-answer="correct"> <label> <input id="q1-6504-1-option-b" name="quiz-option-6504" type="radio" value="how DNA replicated." > <span class="option__label"> <span class="screen-reader-only">b.</span> how DNA replicated. </span> </label> <span class="quiz__response" id="response-6504-1"> <strong>Correct!</strong> </span> </div> </div> </div> </div> </form> </div> </section> <section id="toc_2"> <h2>Design of the Meselson and Stahl experiment</h2><p>This changed when Matthew Meselson and Franklin Stahl, two scientists working at the California Institute of Technology (CalTech), constructed an ingenious <mark class="term" data-term="experiment" data-term-def="A test or trial carried out under controlled conditions so that specific actions can be performed and the results can be observed." data-term-url="/en/glossary/view/experiment/8292">experiment</mark> that tested all three <mark class="term" data-term="model" data-term-def="A representation, pattern, or mathematical description that can help scientists replicate a system." data-term-url="/en/glossary/view/model/8236">models</mark> at the same time. To understand how this experiment worked, it is important to remember how atomic <mark class="term" data-term="isotope" data-term-def="Atoms of the same element with different numbers of neutrons in their atomic nucleus. Isotopes have the same chemical properties and&hellip;" data-term-url="/en/glossary/view/isotope/1516">isotopes</mark> behave. Although a heavier isotope of a given <mark class="term" data-term="atom" data-term-def="The smallest unit of an element that retains the chemical properties of the element. Atoms can exist alone or in&hellip;" data-term-url="/en/glossary/view/atom/1509">atom</mark> behaves in a completely normal manner in <mark class="term" data-term="chemical reaction" data-term-def="A process in which atoms and molecules recombine by forming or breaking chemical bonds. Chemical reactions form new products that&hellip;" data-term-url="/en/glossary/view/chemical+reaction/1547">chemical reactions</mark>, the presence of an extra <mark class="term" data-term="neutron" data-term-def="A sub-atomic particle with no charge and a mass of 1.675 × 10<sup>-27</sup> kg. Neutrons are found in the nucleus&hellip;" data-term-url="/en/glossary/view/neutron/1520">neutron</mark> (or more) gives the atom a slightly higher <mark class="term" data-term="atomic mass" data-term-def="The average mass of an atom of an element, usually expressed in atomic mass units. The term is often used interchangeably&hellip;" data-term-url="/en/glossary/view/atomic+mass/1513">atomic mass</mark>. As a result, <mark class="term" data-term="molecule" data-term-def="A particle formed by the chemical bonding of two or more atoms. The molecule is the smallest particle of a&hellip;" data-term-url="/en/glossary/view/molecule/1518">molecules</mark> that contain these "heavy" isotopes are more <mark class="term" data-term="dense" data-term-def="Compact, packed close together; having a high mass in relation to volume." data-term-url="/en/glossary/view/dense/8273">dense</mark>. This small difference in <mark class="term" data-term="density" data-term-def="A measure of the compactness of a substance given by the mass per unit volume (d = m/v). Common units of&hellip;" data-term-url="/en/glossary/view/density/863">density</mark> allows scientists to physically separate molecules with different isotopes based on the differences in their density.</p><p>For their <mark class="term" data-term="experiment" data-term-def="A test or trial carried out under controlled conditions so that specific actions can be performed and the results can be observed." data-term-url="/en/glossary/view/experiment/8292">experiment</mark>, Meselson and Stahl used a special form of nitrogen: <sup>15</sup>N. Normally, almost all of the nitrogen in any given <mark class="term" data-term="cell" data-term-def="The basic structural unit of all living things." data-term-url="/en/glossary/view/cell/8286">cell</mark> is <sup>14</sup>N and thus contains seven <mark class="term" data-term="neutron" data-term-def="A sub-atomic particle with no charge and a mass of 1.675 × 10<sup>-27</sup> kg. Neutrons are found in the nucleus&hellip;" data-term-url="/en/glossary/view/neutron/1520">neutrons</mark> in addition to its seven <mark class="term" data-term="proton" data-term-def="A subatomic (ß link to atom) particle with a positive charge of 1.60 × 10<sup>-19</sup> coulombs and a mass of 1.672&hellip;" data-term-url="/en/glossary/view/proton/854">protons</mark>. So, <sup>15</sup>N, with eight neutrons, is considered "heavy nitrogen" (but it is not radioactive). When growing cells are fed heavy nitrogen, the <sup>15</sup>N <mark class="term" data-term="isotope" data-term-def="Atoms of the same element with different numbers of neutrons in their atomic nucleus. Isotopes have the same chemical properties and&hellip;" data-term-url="/en/glossary/view/isotope/1516">isotope</mark> enters the cells' <mark class="term" data-term="metabolism" data-term-def="A sequence of biochemical reactions in living organisms that converts food into energy used to drive other biological processes. Also, the&hellip;" data-term-url="/en/glossary/view/metabolism/1606">metabolism</mark> and significant amounts of it will be incorporated into the nitrogen-rich <mark class="term" data-term="nucleotide" data-term-def="The building blocks of DNA and RNA, consisting of a nitrogen base, a five-carbon sugar, and one or more phosphate groups." data-term-url="/en/glossary/view/nucleotide/1603">nucleotides</mark> and <mark class="term" data-term="DNA" data-term-def="Deoxyribonucleic acid. A double-stranded nucleic acid containing the sugar 2-deoxy-D-ribose. A constituent of cellular nuclear material responsible for encoding&hellip;" data-term-url="/en/glossary/view/DNA/1604">DNA</mark>. Thus, the DNA of cells grown with <sup>15</sup>N in their food source would be more <mark class="term" data-term="dense" data-term-def="Compact, packed close together; having a high mass in relation to volume." data-term-url="/en/glossary/view/dense/8273">dense</mark> than that of normal cells. The power of having DNA of different densities is that they can be separated by <mark class="term" data-term="centrifugation" data-term-def="The process of uses a rotating force to separate particles according to density." data-term-url="/en/glossary/view/centrifugation/8514">centrifugation</mark>.</p><p>For this procedure, <mark class="term" data-term="cell" data-term-def="The basic structural unit of all living things." data-term-url="/en/glossary/view/cell/8286">cells</mark> were first broken open; then the cellular contents (called the "crude extract") were mixed with a <mark class="term" data-term="solution" data-term-def="A mixture of more than one substance with properties that do not vary within the sample. Commonly used to describe a&hellip;" data-term-url="/en/glossary/view/solution/1571">solution</mark> of the heavy <mark class="term" data-term="salt" data-term-def="Generally, any ionic compound except those that contain hydroxide or hydrogen ions. Specifically, any compound other than water formed by&hellip;" data-term-url="/en/glossary/view/salt/1575">salt</mark> cesium chloride and placed in a centrifuge cell with clear <mark class="term" data-term="quartz" data-term-def="A common mineral compound made of silica." data-term-url="/en/glossary/view/quartz/8524">quartz</mark> walls that allowed the solution to be photographed while spinning. The cell was then spun in a centrifuge at very high speeds for many hours and the heavy cesium <mark class="term" data-term="ion" data-term-def="An atom or molecule that has acquired an electrical charge by either gaining or losing electrons. A cation is an ion&hellip;" data-term-url="/en/glossary/view/ion/853">ions</mark> were pulled towards the bottom of the cell by centrifugal <mark class="term" data-term="force" data-term-def="An influence (a "push or pull") that changes the motion of a moving object (e.g., slows it down, speeds it up,&hellip;" data-term-url="/en/glossary/view/force/883">force</mark>. Eventually, <mark class="term" data-term="equilibrium" data-term-def="A state of balance between opposing forces; a state of balance in which opposing forces cancel one another. A state in&hellip;" data-term-url="/en/glossary/view/equilibrium/8680">equilibrium</mark> was reached and a "density gradient" was established in the cell with the bottom containing the highest <mark class="term" data-term="concentration" data-term-def="The amount of one substance in relation to other components within a given area." data-term-url="/en/glossary/view/concentration/8733">concentration</mark> of cesium and the top of the tube containing the lowest. Inside a <mark class="term" data-term="density" data-term-def="A measure of the compactness of a substance given by the mass per unit volume (d = m/v). Common units of&hellip;" data-term-url="/en/glossary/view/density/863">density</mark> gradient like this, all the <mark class="term" data-term="molecule" data-term-def="A particle formed by the chemical bonding of two or more atoms. The molecule is the smallest particle of a&hellip;" data-term-url="/en/glossary/view/molecule/1518">molecules</mark> from the cell extract, including the <mark class="term" data-term="DNA" data-term-def="Deoxyribonucleic acid. A double-stranded nucleic acid containing the sugar 2-deoxy-D-ribose. A constituent of cellular nuclear material responsible for encoding&hellip;" data-term-url="/en/glossary/view/DNA/1604">DNA</mark>, will "float" or "sink," migrating to the spot in the gradient that corresponds to their density. The most <mark class="term" data-term="dense" data-term-def="Compact, packed close together; having a high mass in relation to volume." data-term-url="/en/glossary/view/dense/8273">dense</mark> molecules will be pulled toward the bottom of the cell, while less dense molecules will settle higher in the cell, as shown in Figure 2.</p>  <div class="figure"> <figure> <button class="lightbox-button" data-lightbox-src="/img/library/large_images/image_5560.jpg" data-lightbox="image"> <img src="/img/library/modules/mid187/Image/VLObject-5560-110727100709.jpg" alt="Figure 2: The principle of density gradient centrifugation. When a liquid solution containing many large protein and DNA components is placed into a test tube or centrifuge cell and spun at high speed over many hours, the individual molecules separate based on their density. The most dense molecules fall to the bottom, the least dense remain at the top." /> </button> <figcaption> <p><b><strong>Figure 2:</strong> The principle of density gradient centrifugation.</b> When a liquid solution containing many large protein and DNA components is placed into a test tube or centrifuge cell and spun at high speed over many hours, the individual molecules separate based on their density. The most dense molecules fall to the bottom, the least dense remain at the top.</p> <span class="credit">image ©N. Lents</span> </figcaption> </figure> </div> <p>Before beginning their <mark class="term" data-term="analysis" data-term-def="The careful study of data to look for patterns." data-term-url="/en/glossary/view/analysis/8553">analysis</mark> of <mark class="term" data-term="DNA" data-term-def="Deoxyribonucleic acid. A double-stranded nucleic acid containing the sugar 2-deoxy-D-ribose. A constituent of cellular nuclear material responsible for encoding&hellip;" data-term-url="/en/glossary/view/DNA/1604">DNA</mark> <mark class="term" data-term="replication" data-term-def="In science, quality research studies are designed such that the exact procedures and methods followed by the scientists are clear and&hellip;" data-term-url="/en/glossary/view/replication/3730">replication</mark>, Meselson and Stahl first showed that DNA made with regular <sup>14</sup>N could be separated from DNA containing heavy <sup>15</sup>N. They accomplished this by growing two separate batches of <em>Escherichia coli</em> <mark class="term" data-term="bacteria" data-term-def="(plural of bacterium) A large group of one-celled organisms that are found almost everywhere." data-term-url="/en/glossary/view/bacteria/8679">bacteria</mark>, feeding each batch a different nitrogen <mark class="term" data-term="isotope" data-term-def="Atoms of the same element with different numbers of neutrons in their atomic nucleus. Isotopes have the same chemical properties and&hellip;" data-term-url="/en/glossary/view/isotope/1516">isotope</mark>. Then, they broke the bacterial <mark class="term" data-term="cell" data-term-def="The basic structural unit of all living things." data-term-url="/en/glossary/view/cell/8286">cells</mark> open, mixed the extracts from both batches into one centrifuge cell, and spun it to establish the <mark class="term" data-term="density" data-term-def="A measure of the compactness of a substance given by the mass per unit volume (d = m/v). Common units of&hellip;" data-term-url="/en/glossary/view/density/863">density</mark> gradient. To detect the DNA, they shined <mark class="term" data-term="ultraviolet" data-term-def="Wavelengths between 1 and 380 nanometers (nm) on the electromagnetic spectrum, falling between X-rays (10<sup>-2</sup> nm to 1 nm) and visible&hellip;" data-term-url="/en/glossary/view/ultraviolet/8233">ultraviolet</mark> (UV) <mark class="term" data-term="light" data-term-def="A form of electromagnetic radiation. Visible light is that associated with stimulating the organs of sight, which for normal human&hellip;" data-term-url="/en/glossary/view/light/1498">light</mark> on the spinning centrifuge cell because DNA <mark class="term" data-term="absorb" data-term-def="Take in or soak up (energy, liquids, or other substances), usually gradually, through a chemical or physical action." data-term-url="/en/glossary/view/absorb/11219">absorbs</mark> UV light and thus casts a shadow during exposure of photographic film. Below, in Figure 3, is a black-and-white image of their <mark class="term" data-term="data" data-term-def="(plural form of <b>datum</b>) A collection of pieces of information, generally taking the form of numbers, text, bits, or facts, that&hellip;" data-term-url="/en/glossary/view/data/3729">data</mark>, and you can clearly see two bands of DNA, one lower in the cell and thus, more <mark class="term" data-term="dense" data-term-def="Compact, packed close together; having a high mass in relation to volume." data-term-url="/en/glossary/view/dense/8273">dense</mark> than the other.</p> <div class="container margin-y-4 text-align-center"> <script async src="https://pagead2.googlesyndication.com/pagead/js/adsbygoogle.js?client=ca-pub-9561344156007092" crossorigin="anonymous"></script>  <ins class="adsbygoogle" style="display:inline-block;width:300px;height:250px" data-ad-client="ca-pub-9561344156007092" data-ad-slot="3321739899"></ins> <script> (adsbygoogle = window.adsbygoogle || []).push({}); </script> </div>  <div class="figure"> <figure> <button class="lightbox-button" data-lightbox-src="/img/library/large_images/image_5562.png" data-lightbox="image"> <img src="/img/library/modules/mid187/Image/VLObject-5562-110727100713.png" alt="Figure 3: Density gradient centrifugation of a mixture of 15N-DNA and 14N-DNA. Meselson and Stahl first showed that they can separate a mixture of DNA of the two different densities. The picture on the left is a UV photograph showing the banding of DNA of different densities following centrifugation. The graph on the right is a trace of the intensity of the bands in the picture." /> </button> <figcaption> <p><b><strong>Figure 3:</strong> Density gradient centrifugation of a mixture of <sup>15</sup>N-DNA and <sup>14</sup>N-DNA.</b> Meselson and Stahl first showed that they can separate a mixture of DNA of the two different densities. The picture on the left is a UV photograph showing the banding of DNA of different densities following centrifugation. The graph on the right is a trace of the intensity of the bands in the picture.</p> <span class="credit">image ©Meselson and Stahl</span> </figcaption> </figure> </div> <div class="comprehension-checkpoint margin-y-4"> <h6 class="comprehension-checkpoint__header"> <span> <span class="icon icon-question"></span> </span> Comprehension Checkpoint </h6> <form name="cc6506"> <div class="form-entry"> <div class="form-entry__field"> <span class="form-entry__field__label">Meselson and Stahl used <sup>15</sup>N because it caused DNA molecules to become</span> <div class="form-entry__option"> <div class="form-entry__option__radio" data-answer="correct"> <label> <input id="q1-6506-0-option-a" name="quiz-option-6506" type="radio" value="more dense." > <span class="option__label"> <span class="screen-reader-only">a.</span> more dense. </span> </label> <span class="quiz__response" id="response-6506-0"> <strong>Correct!</strong> </span> </div> <div class="form-entry__option__radio" data-answer="incorrect"> <label> <input id="q1-6506-1-option-b" name="quiz-option-6506" type="radio" value="radioactive." > <span class="option__label"> <span class="screen-reader-only">b.</span> radioactive. </span> </label> <span class="quiz__response" id="response-6506-1"> <strong>Incorrect.</strong> </span> </div> </div> </div> </div> </form> </div> </section> <section id="toc_3"> <h2>How the <mark class="term" data-term="experiment" data-term-def="A test or trial carried out under controlled conditions so that specific actions can be performed and the results can be observed." data-term-url="/en/glossary/view/experiment/8292">experiment</mark> tested all three DNA replication hypotheses</h2><p>Next, Meselson and Stahl did something interesting. They grew a large batch of <mark class="term" data-term="bacteria" data-term-def="(plural of bacterium) A large group of one-celled organisms that are found almost everywhere." data-term-url="/en/glossary/view/bacteria/8679">bacteria</mark> in heavy nitrogen (<sup>15</sup>N) and then switched the bacteria to a diet that contained only regular nitrogen (<sup>14</sup>N). This allowed them to distinguish between pre-existing <mark class="term" data-term="DNA" data-term-def="Deoxyribonucleic acid. A double-stranded nucleic acid containing the sugar 2-deoxy-D-ribose. A constituent of cellular nuclear material responsible for encoding&hellip;" data-term-url="/en/glossary/view/DNA/1604">DNA</mark> from the parental <mark class="term" data-term="cell" data-term-def="The basic structural unit of all living things." data-term-url="/en/glossary/view/cell/8286">cells</mark> and newly synthesized DNA, because any newly synthesized DNA strands would contain <sup>14</sup>N and be less <mark class="term" data-term="dense" data-term-def="Compact, packed close together; having a high mass in relation to volume." data-term-url="/en/glossary/view/dense/8273">dense</mark>. They used this experimental set up to put the three possible <mark class="term" data-term="model" data-term-def="A representation, pattern, or mathematical description that can help scientists replicate a system." data-term-url="/en/glossary/view/model/8236">models</mark> of DNA <mark class="term" data-term="replication" data-term-def="In science, quality research studies are designed such that the exact procedures and methods followed by the scientists are clear and&hellip;" data-term-url="/en/glossary/view/replication/3730">replication</mark> to the test.</p><p>Like all proper scientific <mark class="term" data-term="hypothesis" data-term-url="/en/glossary/view/hypothesis" data-term-def="From the Greek word <em>hypothesis</em> meaning assumption or the basis of an argument, a hypothesis is a proposal intended to explain&hellip;">hypotheses</mark>, the three <mark class="term" data-term="model" data-term-def="A representation, pattern, or mathematical description that can help scientists replicate a system." data-term-url="/en/glossary/view/model/8236">models</mark> of <mark class="term" data-term="DNA" data-term-def="Deoxyribonucleic acid. A double-stranded nucleic acid containing the sugar 2-deoxy-D-ribose. A constituent of cellular nuclear material responsible for encoding&hellip;" data-term-url="/en/glossary/view/DNA/1604">DNA</mark> <mark class="term" data-term="replication" data-term-def="In science, quality research studies are designed such that the exact procedures and methods followed by the scientists are clear and&hellip;" data-term-url="/en/glossary/view/replication/3730">replication</mark> each make certain predictions, and testing hypothetical predictions is a key part of scientific <mark class="term" data-term="research" data-term-def="A study or an investigation." data-term-url="/en/glossary/view/research/8257">research</mark>. In the case of Meselson and Stahl's <mark class="term" data-term="experiment" data-term-def="A test or trial carried out under controlled conditions so that specific actions can be performed and the results can be observed." data-term-url="/en/glossary/view/experiment/8292">experiment</mark>, the predictions that each of these models makes are as follows. If the conservative model of DNA replication is true, then one would predict that the bacterial <mark class="term" data-term="cell" data-term-def="The basic structural unit of all living things." data-term-url="/en/glossary/view/cell/8286">cells</mark> grown for one <mark class="term" data-term="generation" data-term-def="Offspring at the same step in the line of descent from a common ancestor." data-term-url="/en/glossary/view/generation/8293">generation</mark> (20 minutes) with <sup>14</sup>N would have two different kinds of DNA: the original DNA would be the <mark class="term" data-term="density" data-term-def="A measure of the compactness of a substance given by the mass per unit volume (d = m/v). Common units of&hellip;" data-term-url="/en/glossary/view/density/863">density</mark> of DNA grown with only <sup>15</sup>N nitrogen, while both strands of the new DNA <mark class="term" data-term="molecule" data-term-def="A particle formed by the chemical bonding of two or more atoms. The molecule is the smallest particle of a&hellip;" data-term-url="/en/glossary/view/molecule/1518">molecules</mark> would be the lighter <sup>14</sup>N DNA band. However, if either the semi-conservative or the dispersive models of DNA replication are correct, the double-stranded DNA inside the <mark class="term" data-term="bacteria" data-term-def="(plural of bacterium) A large group of one-celled organisms that are found almost everywhere." data-term-url="/en/glossary/view/bacteria/8679">bacteria</mark> after one generation would be a mixture of old and new DNA, and thus, one strand would be made of <sup>15</sup>N and one of <sup>14</sup>N DNA. Thus, this "hybrid" DNA would be an intermediate density halfway between the <sup>14</sup>N and <sup>15</sup>N bands of DNA. In Figure 4 below, you can see what the three models of DNA replication predict will happen in the Meselson and Stahl experiment, followed by what they actually observed.</p>  <div class="figure"> <figure> <button class="lightbox-button" data-lightbox-src="/img/library/large_images/image_5565.jpg" data-lightbox="image"> <img src="/img/library/modules/mid187/Image/VLObject-5565-110727100721.jpg" alt="Figure 4: Density gradient centrifugation of E. coli DNA after one cell division. Top panel: the three experimental predictions of three competing models of DNA replication. Bottom panel: The actual data. E. coli grown in 15N DNA were switched to 14N and then harvested at five different time points. The DNA was centrifuged resulting in the banding pattern shown here." /> </button> <figcaption> <p><b><strong>Figure 4:</strong> Density gradient centrifugation of <em>E. coli</em> DNA after one cell division.</b> Top panel: the three experimental predictions of three competing models of DNA replication. Bottom panel: The actual data. <em>E. coli</em> grown in <sup>15</sup>N DNA were switched to <sup>14</sup>N and then harvested at five different time points. The DNA was centrifuged resulting in the banding pattern shown here.</p> <span class="credit">image ©N. Lents/Meselson and Stahl</span> </figcaption> </figure> </div> <p>As you can see from their results above, after one <mark class="term" data-term="generation" data-term-def="Offspring at the same step in the line of descent from a common ancestor." data-term-url="/en/glossary/view/generation/8293">generation</mark> of <mark class="term" data-term="cell" data-term-def="The basic structural unit of all living things." data-term-url="/en/glossary/view/cell/8286">cell</mark> division, the total <mark class="term" data-term="DNA" data-term-def="Deoxyribonucleic acid. A double-stranded nucleic acid containing the sugar 2-deoxy-D-ribose. A constituent of cellular nuclear material responsible for encoding&hellip;" data-term-url="/en/glossary/view/DNA/1604">DNA</mark> of the growing bacterial cells had an intermediate <mark class="term" data-term="density" data-term-def="A measure of the compactness of a substance given by the mass per unit volume (d = m/v). Common units of&hellip;" data-term-url="/en/glossary/view/density/863">density</mark>, halfway between that of <sup>14</sup>N and <sup>15</sup>N DNA. This strongly disproved the conservative <mark class="term" data-term="model" data-term-def="A representation, pattern, or mathematical description that can help scientists replicate a system." data-term-url="/en/glossary/view/model/8236">model</mark> of DNA, which held that the original two strands of DNA would persist and remain bound to each other and a wholly new copy of two DNA strands would be synthesized. In other words, the conservative model of DNA <mark class="term" data-term="replication" data-term-def="In science, quality research studies are designed such that the exact procedures and methods followed by the scientists are clear and&hellip;" data-term-url="/en/glossary/view/replication/3730">replication</mark> would predict that, after one generation, half of the DNA <mark class="term" data-term="molecule" data-term-def="A particle formed by the chemical bonding of two or more atoms. The molecule is the smallest particle of a&hellip;" data-term-url="/en/glossary/view/molecule/1518">molecules</mark> would have only <sup>15</sup>N DNA and half would have <sup>14</sup>N DNA, which would appear as two distinct bands of DNA density. But as seen above, all DNA molecules were of intermediate density. However, the two remaining models, semi-conservative and dispersive, were still consistent with these results. In order to examine the two remaining models of DNA replication, we must examine additional generations of bacterial growth with the normal <sup>14</sup>N <mark class="term" data-term="isotope" data-term-def="Atoms of the same element with different numbers of neutrons in their atomic nucleus. Isotopes have the same chemical properties and&hellip;" data-term-url="/en/glossary/view/isotope/1516">isotope</mark> of nitrogen. In Figure 5 below are the predictions of all three models of DNA replication, over multiple generations:</p>  <div class="figure"> <figure> <button class="lightbox-button" data-lightbox-src="/img/library/large_images/image_5567.jpg" data-lightbox="image"> <img src="/img/library/modules/mid187/Image/VLObject-5567-110727100736.jpg" alt="Figure 5: Experimental predictions of three competing models of DNA replication over three generations." /> </button> <figcaption> <p><b>Figure 5:</b> Experimental predictions of three competing models of DNA replication over three generations.</p> <span class="credit">image ©N. Lents</span> </figcaption> </figure> </div> <p>And now, here are the actual <mark class="term" data-term="observation" data-term-def="1. The act of noticing something. 2. A record of that which has been noticed." data-term-url="/en/glossary/view/observation/8255">observations</mark> of Meselson and Stahl (Figure 6):</p>  <div class="figure"> <figure> <button class="lightbox-button" data-lightbox-src="/img/library/large_images/image_5569.jpg" data-lightbox="image"> <img src="/img/library/modules/mid187/Image/VLObject-5569-110727100752.jpg" alt="Figure 6: Density gradient centrifugation of E. coli DNA over multiple generations. E. coli grown in 15N DNA were switched to 14N and then harvested at nine different time points. The DNA was centrifuged resulting in the banding pattern shown here." /> </button> <figcaption> <p><b><strong>Figure 6:</strong> Density gradient centrifugation of <em>E. coli</em> DNA over multiple generations.</b> <em>E. coli</em> grown in <sup>15</sup>N DNA were switched to <sup>14</sup>N and then harvested at nine different time points. The DNA was centrifuged resulting in the banding pattern shown here.</p> <span class="credit">image ©Meselson and Stahl</span> </figcaption> </figure> </div> <p>As they let the bacterial <mark class="term" data-term="cell" data-term-def="The basic structural unit of all living things." data-term-url="/en/glossary/view/cell/8286">cells</mark> grow and divide further, Meselson and Stahl observed that the <sup>15</sup>N <mark class="term" data-term="DNA" data-term-def="Deoxyribonucleic acid. A double-stranded nucleic acid containing the sugar 2-deoxy-D-ribose. A constituent of cellular nuclear material responsible for encoding&hellip;" data-term-url="/en/glossary/view/DNA/1604">DNA</mark> band disappeared, a band of <sup>14</sup>N DNA appeared and then got progressively darker, and a band of intermediate <mark class="term" data-term="density" data-term-def="A measure of the compactness of a substance given by the mass per unit volume (d = m/v). Common units of&hellip;" data-term-url="/en/glossary/view/density/863">density</mark> appeared and persisted at about the same intensity. This strongly discredited the dispersive <mark class="term" data-term="model" data-term-def="A representation, pattern, or mathematical description that can help scientists replicate a system." data-term-url="/en/glossary/view/model/8236">model</mark> of DNA <mark class="term" data-term="replication" data-term-def="In science, quality research studies are designed such that the exact procedures and methods followed by the scientists are clear and&hellip;" data-term-url="/en/glossary/view/replication/3730">replication</mark>, which predicted that only one band of DNA would exist and would get progressively less <mark class="term" data-term="dense" data-term-def="Compact, packed close together; having a high mass in relation to volume." data-term-url="/en/glossary/view/dense/8273">dense</mark> as the amount of <sup>14</sup>N DNA in the dispersive mixture increased with each <mark class="term" data-term="generation" data-term-def="Offspring at the same step in the line of descent from a common ancestor." data-term-url="/en/glossary/view/generation/8293">generation</mark>. Thus, in one simple <mark class="term" data-term="experiment" data-term-def="A test or trial carried out under controlled conditions so that specific actions can be performed and the results can be observed." data-term-url="/en/glossary/view/experiment/8292">experiment</mark> with very clear results, Meselson and Stahl solidly disproved two of the possible models of DNA replication, while strongly supporting another.</p> <div class="comprehension-checkpoint margin-y-4"> <h6 class="comprehension-checkpoint__header"> <span> <span class="icon icon-question"></span> </span> Comprehension Checkpoint </h6> <form name="cc6508"> <div class="form-entry"> <div class="form-entry__field"> <span class="form-entry__field__label">The Meselson and Stahl experiment supported one hypothesis of DNA replication</span> <div class="form-entry__option"> <div class="form-entry__option__radio" data-answer="correct"> <label> <input id="q1-6508-0-option-a" name="quiz-option-6508" type="radio" value="and disproved the other two hypotheses." > <span class="option__label"> <span class="screen-reader-only">a.</span> and disproved the other two hypotheses. </span> </label> <span class="quiz__response" id="response-6508-0"> <strong>Correct!</strong> </span> </div> <div class="form-entry__option__radio" data-answer="incorrect"> <label> <input id="q1-6508-1-option-b" name="quiz-option-6508" type="radio" value="but could not disprove the other two hypotheses." > <span class="option__label"> <span class="screen-reader-only">b.</span> but could not disprove the other two hypotheses. </span> </label> <span class="quiz__response" id="response-6508-1"> <strong>Incorrect.</strong> </span> </div> </div> </div> </div> </form> </div> </section> <section id="toc_4"> <h2>"The most beautiful <mark class="term" data-term="experiment" data-term-def="A test or trial carried out under controlled conditions so that specific actions can be performed and the results can be observed." data-term-url="/en/glossary/view/experiment/8292">experiment</mark> in biology"</h2><p>The scientific community agreed that this was powerful <mark class="term" data-term="evidence" data-term-def="Support for an idea, opinion, or hypothesis." data-term-url="/en/glossary/view/evidence/8243">evidence</mark> in support of the semi-conservative <mark class="term" data-term="model" data-term-def="A representation, pattern, or mathematical description that can help scientists replicate a system." data-term-url="/en/glossary/view/model/8236">model</mark>. John Cairns, one of the leading molecular biologists of the era, called it, "the most beautiful <mark class="term" data-term="experiment" data-term-def="A test or trial carried out under controlled conditions so that specific actions can be performed and the results can be observed." data-term-url="/en/glossary/view/experiment/8292">experiment</mark> in biology." To this day, the Meselson and Stahl experiment is taught around the world as a classic example of the modern scientific <mark class="term" data-term="method" data-term-def="A procedure or process; a systematic way of performing a task or conducting research." data-term-url="/en/glossary/view/method/8238">method</mark> of experimentation. With one simple design, three scientific <mark class="term" data-term="hypothesis" data-term-url="/en/glossary/view/hypothesis" data-term-def="From the Greek word <em>hypothesis</em> meaning assumption or the basis of an argument, a hypothesis is a proposal intended to explain&hellip;">hypotheses</mark> were tested by the observation/verification of their predictions.</p><p>Scientists now have a detailed understanding of the molecular events of <mark class="term" data-term="DNA" data-term-def="Deoxyribonucleic acid. A double-stranded nucleic acid containing the sugar 2-deoxy-D-ribose. A constituent of cellular nuclear material responsible for encoding&hellip;" data-term-url="/en/glossary/view/DNA/1604">DNA</mark> <mark class="term" data-term="replication" data-term-def="In science, quality research studies are designed such that the exact procedures and methods followed by the scientists are clear and&hellip;" data-term-url="/en/glossary/view/replication/3730">replication</mark> (see our <a href="http://www.visionlearning.com/library/module_viewer.php?mid=180&l=">DNA III</a> module). These molecular events occur just as predicted by the Watson and Crick <mark class="term" data-term="model" data-term-def="A representation, pattern, or mathematical description that can help scientists replicate a system." data-term-url="/en/glossary/view/model/8236">model</mark> of DNA structure, and verify that the semi-conservative model of DNA replication is indeed correct. The Meselson and Stahl technique of labeling DNA strands with nitrogen <mark class="term" data-term="isotope" data-term-def="Atoms of the same element with different numbers of neutrons in their atomic nucleus. Isotopes have the same chemical properties and&hellip;" data-term-url="/en/glossary/view/isotope/1516">isotopes</mark> is still employed by scientists around the world as they continue to explore the mysteries and complexities of DNA, the genetic material of life.</p></section> <footer class="module__main__footer"> <hr class="border-color-dark"> <p class="citation"> <em> Nathan H Lents, Ph.D. “An Elegant Experiment to Test the Process of DNA Replication” Visionlearning Vol. SCIRE-1 (6), 2011. </em> </p>  <div class="title-list" id="refs" name="refs"> <p class="h6 title-list__title"> References </p> <ul class="title-list__list"> <li>Meselson, M. and Stahl, F.W. (1958). "The Replication of DNA in Escherichia coli." <em>Proceedings of the National Academy of Sciences, 44</em>(7): 671-82. doi:10.1073/pnas.44.7.671.PMID 16590258.</li> <li>Holmes, F.L. (2001). <em>Meselson, Stahl, and the replication of DNA: A history of "the most beautiful experiment in biology".</em> New Haven, CT: Yale University Press.</li> </ul> </div>  <div class="title-list" name="further"> <p class="h6 title-list__title"> Further Reading </p> <ul class="grid grid--column-2--md grid--column-3--md gap-1"> <li> <a class="no-hover-focus height-100" href="/en/library/Biology/2/DNA-I/149"> <article class="flex-row align-items-center flex-column--md align-items-start--md height-100 theme-light padding-2 gap-2"> <div class="width-30 width-auto--md"> <img class="border-radius box-shadow-1" src="/img/library/moduleImages/featured_image_149-23061209063622.png" alt="DNA I"> </div> <div class="flex-grow-shrink"> <h2 class="h6 font-weight-normal"> DNA I: <em>The genetic material</em> </h2> </div> </article> </a> </li> <li> <a class="no-hover-focus height-100" href="/en/library/Biology/2/DNA-II/160"> <article class="flex-row align-items-center flex-column--md align-items-start--md height-100 theme-light padding-2 gap-2"> <div class="width-30 width-auto--md"> <img class="border-radius box-shadow-1" src="/img/library/moduleImages/featured_image_160-23061209063635.jpg" alt="DNA II"> </div> <div class="flex-grow-shrink"> <h2 class="h6 font-weight-normal"> DNA II: <em>The structure of DNA</em> </h2> </div> </article> </a> </li> <li> <a class="no-hover-focus height-100" href="/en/library/Inside-Science/58/From-Stable-Chromosomes-to-Jumping-Genes/184"> <article class="flex-row align-items-center flex-column--md align-items-start--md height-100 theme-light padding-2 gap-2"> <div class="width-30 width-auto--md"> <img class="border-radius box-shadow-1" src="/img/library/moduleImages/featured_image_184-23061210063845.jpeg" alt="From Stable Chromosomes to Jumping Genes"> </div> <div class="flex-grow-shrink"> <h2 class="h6 font-weight-normal"> From Stable Chromosomes to Jumping Genes: <em>The work of Barbara McClintock</em> </h2> </div> </article> </a> </li> <li> <a class="no-hover-focus height-100" href="/en/library/Process-of-Science/49/Creativity-in-Science/182"> <article class="flex-row align-items-center flex-column--md align-items-start--md height-100 theme-light padding-2 gap-2"> <div class="width-30 width-auto--md"> <img class="border-radius box-shadow-1" src="/img/library/moduleImages/featured_image_182-23061210061345.jpg" alt="Creativity in Science"> </div> <div class="flex-grow-shrink"> <h2 class="h6 font-weight-normal"> Creativity in Science: <em>How scientists decide what to study</em> </h2> </div> </article> </a> </li> </ul> </div> </footer> </div>    </article> </div> </div> </main>   <footer class="position-relative box-shadow-1 font-size-md" id="global-footer"> <h2 class="screen-reader-only">Page Footer</h2> <div class="back-to-top"> <div class="container wide"> <button class="button button--has-icon font-size-sm"> <span class="icon icon-arrow-up"></span> <span class="button__text">Back to top</span> </button> </div> </div> <div class="container wide padding-y-2"> <div class="grid grid--column-2--md grid--column-4--lg gap-4 grid--divider--fill-x"> <nav> <ul class="nav font-weight-bold"> <li> <a href="/en/library" title="Readings & quizzes"> Library </a> </li> <li> <a href="/en/glossary" title="Science terms"> Glossary </a> </li> <li> <a href="/en/classroom" title="Courses & bookmarks"> Classroom </a> </li> </ul> </nav> <nav> <ul class="nav"> <li><a href="/en/about">About</a></li> <li><a href="/en/help">Contact</a></li> <li><a href="/en/about/jobs">Jobs</a></li> <li><a href="/en/help/faq">FAQ</a></li> </ul> </nav> <div> <ul class="nav nav--horizontal margin-bottom-2"> <li> <a class="display-flex" href="https://www.nsf.gov" target="_blank" rel="noopener"> <img src="/images/sponsor-nsf.png" width="60" height="60" alt="US Education Department Logo" /> </a> </li> <li> <a class="display-flex" href="https://www.ed.gov/" target="_blank" rel="noopener"> <img src="/images/sponsor-doe.png" width="60" height="60" alt="US Education Department Logo" /> </a> </li> </ul> <p>Visionlearning is supported by the The National Science Foundation and the U.S. Department of Education. 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An Elegant Experiment to Test the Process of DNA Replication | Scientists and Research | Visionlearning