Cell Division I | Biology | Visionlearning

<!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>Cell Division I | Biology | Visionlearning</title> <link rel="canonical" href="https://www.visionlearning.com/en/library/biology/2/cell-division-i/196"> <meta name="description" content="Learn about one stage of the cell division process. includes detailed information on mitosis, restriction points, and phases."> <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/biology/2/cell-division-i/196" }, "name": "Cell Division I", "headline": "Cell Division I: The cell cycle", "author": [ { "@type": "Person", "name": "Nathan H Lents, Ph.D." } , { "@type": "Person", "name": "Donna Hesterman" }], "datePublished": "2013-11-20 11:50:36", "dateModified": "2017-02-12T08:30:00+05:00", "image": { "@type": "ImageObject", "url": "/img/library/moduleImages/featured_image_196-23061209062737.jpg", "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": "Cell division is an enormously complex process that must go on millions and millions of times during the life of an organism. This module explains the difference between binary fission and the cell division cycle. The stages of cell division are explored, and research that contributed to our understanding of the process is described.", "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": "2013"} </script> <meta property="og:url" content="https://visionlearning.com/en/library/biology/2/cell-division-i/196"> <meta property="og:title" content="Cell Division I | Biology | Visionlearning" /> <meta property="og:type" content="website"> <meta property="og:site_name" content="Visionlearning"> <meta property="og:description" content="Learn about one stage of the cell division process. includes detailed information on mitosis, restriction points, and phases."> <meta property="og:image" content="https://visionlearning.com/images/logo.png"> <meta property="fb:admins" 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href="/en/library/earth-science/6/natural-hazards-and-risk/288">Natural Hazards and Risk</a></li> </ul> </div> <button class="accordion__button" id="acc-button-earth-history" data-accordion="button" aria-controls="acc-panel-earth-history" aria-expanded="false"> <span class="accordion__button__label"> Earth History </span> </button> <div class="accordion__panel" id="acc-panel-earth-history" data-accordion="panel" aria-labelledby="acc-button-earth-history" role="region"> <ul class="nav text-color-link"> <li><a href="/en/library/earth-science/6/extinction/295">Extinction</a></li> <li><a href="/en/library/earth-science/6/mass-extinctions/294">Mass Extinctions</a></li> </ul> </div> </div> </div> <button class="accordion__button" id="acc-button-environmental-science" data-accordion="button" aria-controls="acc-panel-environmental-science" aria-expanded="false"> <span class="accordion__button__label"> Environmental Science </span> </button> <div class="accordion__panel" 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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><a href="/en/library/scientists-and-research/58/an-elegant-experiment-to-test-the-process-of-dna-replication/187">An Elegant Experiment to Test the Process of DNA Replication</a></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-díaz/219">Franklin Chang Díaz</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-córdova/230">France Anne-Dominic Córdova</a></li> </ul> </div> </div> </div> </div> </div> </li> <li>  <button class="button" data-toggle="dropdown">Biology </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-biological-molecules" data-accordion="button" aria-controls="acc-sub-panel-biological-molecules" aria-expanded="false"> <span class="accordion__button__label"> Biological Molecules </span> </button> <div class="accordion__panel" id="acc-sub-panel-biological-molecules" data-accordion="panel" aria-labelledby="acc-sub-button-biological-molecules" role="region"> <ul class="nav text-color-link"> <li><a href="/en/library/biology/2/carbohydrates/61">Carbohydrates</a></li> <li><a href="/en/library/biology/2/fats-and-proteins/62">Fats and Proteins</a></li> <li><a href="/en/library/biology/2/biological-proteins/243">Biological Proteins</a></li> <li><a href="/en/library/biology/2/blood-biology-i/242">Blood Biology I</a></li> <li><a href="/en/library/biology/2/lipids/207">Lipids</a></li> </ul> </div> <button class="accordion__button" id="acc-sub-button-cell-biology" data-accordion="button" aria-controls="acc-sub-panel-cell-biology" aria-expanded="false"> <span class="accordion__button__label"> Cell Biology </span> </button> <div class="accordion__panel" id="acc-sub-panel-cell-biology" data-accordion="panel" aria-labelledby="acc-sub-button-cell-biology" role="region"> <ul class="nav text-color-link"> <li><a href="/en/library/biology/2/discovery-and-structure-of-cells/64">Discovery and Structure of Cells</a></li> <li><a href="/en/library/biology/2/respiration/285">Respiration</a></li> <li><a href="/en/library/biology/2/membranes-i/198">Membranes I</a></li> <li><a href="/en/library/biology/2/membranes-ii/204">Membranes II</a></li> <li><a href="/en/library/biology/2/cellular-organelles-i/195">Cellular Organelles I</a></li> <li class="current">Cell Division I</li> <li><a href="/en/library/biology/2/cell-division-ii/212">Cell Division II</a></li> <li><a href="/en/library/biology/2/membranes-and-chemical-transport/106">Membranes and Chemical Transport</a></li> </ul> </div> <button class="accordion__button" id="acc-sub-button-energy-in-living-systems" data-accordion="button" aria-controls="acc-sub-panel-energy-in-living-systems" aria-expanded="false"> <span class="accordion__button__label"> Energy in Living Systems </span> </button> <div class="accordion__panel" id="acc-sub-panel-energy-in-living-systems" data-accordion="panel" aria-labelledby="acc-sub-button-energy-in-living-systems" role="region"> <ul class="nav text-color-link"> <li><a href="/en/library/biology/2/energy-metabolism-i/215">Energy Metabolism I</a></li> <li><a href="/en/library/biology/2/energy-metabolism-ii/225">Energy Metabolism II</a></li> <li><a href="/en/library/biology/2/photosynthesis-i/192">Photosynthesis I</a></li> </ul> </div> <button 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Darwin III</a></li> <li><a href="/en/library/biology/2/adaptation/68">Adaptation</a></li> <li><a href="/en/library/biology/2/taxonomy-i/70">Taxonomy I</a></li> <li><a href="/en/library/biology/2/taxonomy-ii/89">Taxonomy II</a></li> <li><a href="/en/library/biology/2/introduction-to-paleoanthropology/258">Introduction to Paleoanthropology</a></li> <li><a href="/en/library/biology/2/the-piltdown-hoax/263">The Piltdown Hoax</a></li> <li><a href="/en/library/biology/2/future-of-human-evolution/259">Future of Human Evolution</a></li> </ul> </div> <button class="accordion__button" id="acc-sub-button-genetics" data-accordion="button" aria-controls="acc-sub-panel-genetics" aria-expanded="false"> <span class="accordion__button__label"> Genetics </span> </button> <div class="accordion__panel" id="acc-sub-panel-genetics" data-accordion="panel" aria-labelledby="acc-sub-button-genetics" role="region"> <ul class="nav text-color-link"> <li><a 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<p class="byline">by Nathan H Lents, Ph.D., Donna Hesterman</p> <nav class="module__header__tabs"> <ul class="tabs-nav tabs-nav--horizontal library"> <li> <a href="/en/library/biology/2/cell-division-i/196/reading" aria-current="page" >Reading</a> </li> <li> <a href="/en/library/biology/2/cell-division-i/196/quiz">Quiz</a> </li> <li> <a href="/en/library/biology/2/cell-division-i/196/resources">Teach with this</a> </li> </ul> </nav> </div> <script type="application/ld+json"> { "@context": "http://schema.org", "@type": "AudioObject", "contentUrl": "https://www.visionlearning.com/img/library/moduleAudio/module_196.mp3", "description": "Recording of Cell Division I : Cell division is an enormously complex process that must go on millions and millions of times during the life of an organism. This module explains the difference between binary fission and the cell division cycle. The stages of cell division are explored, and research that contributed to our understanding of the process is described.", "encodingFormat": "mp3", "name": "module_196.mp3" } </script> <div class="module_header_audio"> <div class="audio-player border border-radius"> <audio id="audio"> <source src="https://www.visionlearning.com/img/library/moduleAudio/module_196.mp3" type="audio/mpeg"> Your browser does not support the audio element. </audio> <div class="audio-player__title"> <p>Listen to this reading</p> <span class="audio-player__timestamp" id="timestamp"> 00:00 </span> </div> <div class="audio-player__controls" id="controls"> <button class="button button--icon-only" id="play-pause-button"> <span class="icon icon-play" aria-hidden="true"></span> </button> <div class="audio-player__progress" id="progress-bar" tabindex="0" aria-valuemin="0" aria-valuemax="100" aria-valuenow="0" aria-label="Use arrow keys to forward or rewind the audio" role="slider"> <div class="audio-player__progress__fill"> <span class="audio-player__thumb"></span> </div> </div> <div class="audio-player__volume-container"> <button id="mute-button"> <span class="icon icon-volume"></span> </button> <div class="audio-player__volume" tabindex="0" aria-valuemin="0" aria-valuemax="100" aria-valuenow="100" aria-label="Use arrow keys to adjust volume" role="slider"> <div class="audio-player__volume__fill"> <span class="audio-player__thumb"></span> </div> </div> </div> </div> </div> </div> </header> <hr class="divider"/>   <div class="grid grid--sidebar-right grid--divider"> <div class="order-2 order-1--lg module__main"> <div class="narrow margin-x-auto margin-y-5"> <div class="accordion margin-bottom-5">  <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 every organ and tissue in your body was formed as the result of individual cells making copies of their DNA and separating themselves into two identical cells? From experiments in the 1870s to research more than 100 years later, scientists have made fascinating discoveries about the complex series of events that allow the cells in plants and animals, including humans, to grow and sustain life.</p> </div> </div>  <button class="accordion__button" id="acc-button-table-of-contents" data-accordion="button" aria-controls="acc-panel-table-of-contents" aria-expanded="false" tabindex="0"> Key concepts </button> <div class="accordion__panel" id="acc-panel-table-of-contents" data-accordion="panel" aria-labelledby="acc-button-table-of-contents" role="region" aria-hidden="true"> <div class="accordion__panel__content"> <ul class="bulleted"> <li><p>Most of the cells that make up higher organisms, like vertebrate animals and flowering plants, reproduce via a process called cell division.</p></li> <li><p>In cell division, a cell makes a copy of its DNA and then separates itself into two identical cells – each with its own copy of DNA enveloped inside a nucleus.</p></li> <li><p>The term mitosis refers specifically to the process whereby the nucleus of the parent cell splits into two identical nuclei prior to cell division.</p></li> </ul> </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><a href="/en/glossary/view/cell">cell </a></dt> <dd> the basic structural unit of all living things </dd> <dt>eukaryotes </dt> <dd> advanced organisms—including animals, plants, fungi, and protists—whose cells have a nucleus and other membrane-bound organelles. </dd> <dt>phase </dt> <dd> a step or stage in a process </dd> <dt>prokaryotes </dt> <dd> mostly one-celled organisms, bacteria for example, whose cells do not have a nucleus or other membrane-bound organelles.</dd> </dl> </div> </div> </div> <hr class="border-color-dark" /> <section> <div class="container narrow"> <p>It’s hard to imagine, but the <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> present in a tiny embryo ultimately generate all of the cells that make up the body of an adult human being. </p> <p>That’s right, the hundreds of millions 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">cells</mark> that make up the bone and flesh of your body are products of thousands of <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">generations</mark> of cell division that began when you were smaller than the period at the end of this sentence. It started when a single cell cleaved into two parts, then quickly reorganized and split again into four new cells (Figure 1). Four cells became eight; then eight became 16 individual cells with identical <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>. The cascade continued until several weeks later, millions of cells were dividing – powering the exponential pattern of growth that eventually formed all of the organs and tissues of your body.</p> <div class="figure"> <figure> <button class="lightbox-button lightbox-button--icon" data-lightbox=""> <img src="/img/library/modules/mid196/Image/VLObject-6586-131031121010.jpg" alt="Figure 1: Most plant and animal cells replicate by splitting into two identical daughter cells." /> </button> <figcaption> <p><strong>Figure 1:</strong> Most plant and animal cells replicate by splitting into two identical daughter cells.</p> </figcaption> </figure> </div> <p><section id="toc_1" class=""> <h2>The discovery of cell division</h2></p> <p>Walther Flemming (Figure 2), a 19<sup>th</sup> century professor at the Institute for Anatomy in Kiel, Germany, was the first to document the details of cellular division. The use of microscopes to study biological tissues was an emerging technology in Flemming's day, and he was highly regarded as an innovator in the field. </p> <div class="figure"> <figure> <button class="lightbox-button lightbox-button--icon" data-lightbox="" data-lightbox-src="/img/library/large_images/image_6587.jpg"> <img src="/img/library/modules/mid196/Image/VLObject-6587-131031121017.jpg" alt="Figure 2: Walther Flemming" /> </button> <figcaption> <p><strong>Figure 2:</strong> Walther Flemming</p> <span class="credit">image ©Wikimedia Commons</span> </figcaption> </figure> </div> <p>As a professor at Kiel, Flemming experimented with a technique for using dyes to color the specimens he wanted to examine under a microscope. Microscopes in the 1870s were not equipped with electric <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> sources as they are today, so dying the specimens allowed him to see them in greater detail. He found aniline dyes particularly useful because different types of tissues absorbed the dyes at varying intensities depending on their chemistry. The effect was that different parts of 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> would <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">absorb</mark> more dye, in effect "highlighting" them, as in Figure 3, to reveal structures and processes that were invisible before.</p> <div class="figure"> <figure> <button class="lightbox-button lightbox-button--icon" data-lightbox="" data-lightbox-src="/img/library/large_images/image_6588.jpg"> <img src="/img/library/modules/mid196/Image/VLObject-6588-131120101157.jpg" alt="Figure 3: Unstained (right) versus stained cells (left)" /> </button> <figcaption> <p><strong>Figure 3:</strong> Unstained (right) versus stained cells (left)</p> <span class="credit">image ©Judith Beekman</span> </figcaption> </figure> </div> <p>Flemming used these dyes to study <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>. In particular, he was interested in the <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> of cell division. He began a series of live <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> under the microscope using dyed samples of animal tissues and found that a particular <mark class="term" data-term="mass" data-term-def="A fundamental property of matter which is a numerical measure of the inertia of an object or the amount of matter&hellip;" data-term-url="/en/glossary/view/mass/3417">mass</mark> of material inside the <mark class="term" data-term="nucleus" data-term-def="1. [Atomic] A tiny, dense positively charged mass at the heart of an atom. The nucleus is composed of protons and&hellip;" data-term-url="/en/glossary/view/nucleus/1526">nucleus</mark> of cells absorbed the dye quite well. He didn't have a name for it at the time, but later came to call the material "chromatin," from chroma, the Greek word for color (Zacharias, 2013). Flemming drew pictures of what he saw under his microscope to illustrate various publications he produced in his <mark class="term" data-term="research" data-term-def="A study or an investigation." data-term-url="/en/glossary/view/research/8257">research</mark> (Figure 4).</p> <div class="figure"> <figure> <button class="lightbox-button lightbox-button--icon" data-lightbox="" data-lightbox-src="/img/library/large_images/image_6590.jpg"> <img src="/img/library/modules/mid196/Image/VLObject-6590-131031121030.jpg" alt="Figure 4: Flemming's drawing of an insect cell treated with an aniline dye as he saw it under the microscope" /> </button> <figcaption> <p><strong>Figure 4:</strong> Flemming's drawing of an insect cell treated with an aniline dye as he saw it under the microscope</p> <span class="credit">image ©Wikimedia Commons</span> </figcaption> </figure> </div> <p>Flemming did many of his <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> with tissue samples from Fire salamanders, a common <mark class="term" data-term="species" data-term-def="1. In biological classifications, it is the lowest and most basic unit of the Linnaean taxonomic hierarchy (although it is also&hellip;" data-term-url="/en/glossary/view/species/893">species</mark> in Northern European forests, because the <mark class="term" data-term="chromatin" data-term-def="Chromatin is the substance inside of the cell's nucleus and it consists of DNA, proteins (primarily histones), and chromosomal RNA. The&hellip;" data-term-url="/en/glossary/view/chromatin/9839">chromatin</mark> in their nuclei was large in comparison to other available study <mark class="term" data-term="organism" data-term-def="Any connected living system, such as an animal, plant, fungus, or bacterium. Organisms may be composed of a single cell or&hellip;" data-term-url="/en/glossary/view/organism/2171">organisms</mark>. After many hours of <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">observation</mark>, Flemming began to see a pattern whereby <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> would periodically <mark class="term" data-term="transition" data-term-def="A change from one stage, form, or state to another." data-term-url="/en/glossary/view/transition/8520">transition</mark> from a resting stage to a period of frenzied activity that turned one <mark class="term" data-term="nucleus" data-term-def="1. [Atomic] A tiny, dense positively charged mass at the heart of an atom. The nucleus is composed of protons and&hellip;" data-term-url="/en/glossary/view/nucleus/1526">nucleus</mark> into two, and then pulled the entire cell apart creating two identical cells – each with its own complement of chromatin enveloped within its nucleus. </p><p>Today we call the <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> of the <mark class="term" data-term="nucleus" data-term-def="1. [Atomic] A tiny, dense positively charged mass at the heart of an atom. The nucleus is composed of protons and&hellip;" data-term-url="/en/glossary/view/nucleus/1526">nucleus</mark> splitting into two nuclei <em>mitosis,</em> and the <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> split itself, <em>cytokinesis.</em> The terms came into use years after Flemming's discovery, but he described the process fully in his book <em>Zur Kenntniss der Zelle und ihrer Theilungs-Erscheinungen</em> (To the knowledge of the cell and its phenomena of division) (Flemming, 1878).</p></section> <section id="toc_2"> <h2>Cell life cycles</h2><p>The alternating patterns of activity and inactivity that Flemming saw in his samples are now commonly referred to as 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>'s life cycle, or often just called the cell cycle. Different types of animal cells – like bone, skin, heart, or nerve cells – all have different life cycles. Life cycles vary between types of cells, but all <mark class="term" data-term="eukaryotic" data-term-def="Of cells with a nucleus and other organelles that are surrounded by lipid membranes" data-term-url="/en/glossary/view/eukaryotic/6539">eukaryotic</mark> cell cycles can be broken down into four distinct phases: the G<sub>1</sub> phase, when the cell grows in preparation for an eventual split; the S phase, where <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> inside the <mark class="term" data-term="nucleus" data-term-def="1. [Atomic] A tiny, dense positively charged mass at the heart of an atom. The nucleus is composed of protons and&hellip;" data-term-url="/en/glossary/view/nucleus/1526">nucleus</mark> makes a complete copy of itself; the G<sub>2</sub> phase, when the cell checks and corrects any errors that may have occurred during DNA duplication; and an M phase (for mitosis), when the cell’s nucleus splits into two identical nuclei, immediately followed by <mark class="term" data-term="cytokinesis" data-term-def="The process of cell division in the eukaryotic cell cycle, characterized by the cytoplasm dividing to form two daughter cells." data-term-url="/en/glossary/view/cytokinesis/10178">cytokinesis</mark> – cell division. The length and frequency of these phases are different for different types of cells.</p><p>At this point, it is necessary to point out that, while all living <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> are remarkably similar, cell division is one of those areas where <mark class="term" data-term="eukaryotic" data-term-def="Of cells with a nucleus and other organelles that are surrounded by lipid membranes" data-term-url="/en/glossary/view/eukaryotic/6539">eukaryotic</mark> cells (plants, animals, fungi, and protists) are very different than <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> and other <mark class="term" data-term="prokaryote" data-term-def="An organism, generally one-celled, whose cells do not have a nucleus or other membrane-bound organelles, such as bacteria." data-term-url="/en/glossary/view/prokaryote/8677">prokaryotes</mark>. This is because bacteria and other simple cells do not have a <mark class="term" data-term="nucleus" data-term-def="1. [Atomic] A tiny, dense positively charged mass at the heart of an atom. The nucleus is composed of protons and&hellip;" data-term-url="/en/glossary/view/nucleus/1526">nucleus</mark>, so the <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> can be much simpler. In effect, bacteria simply grow and divide continuously with no distinguishable phases between one division and the next. The process by which prokaryotes divide is called <em>binary fission</em>, and the term “mitosis” never applies to them.</p><p>Another difference between <mark class="term" data-term="prokaryote" data-term-def="An organism, generally one-celled, whose cells do not have a nucleus or other membrane-bound organelles, such as bacteria." data-term-url="/en/glossary/view/prokaryote/8677">prokaryotes</mark> and <mark class="term" data-term="eukaryote" data-term-def="A single- or multi-cellular organism whose cells contain a distinct nucleus that encloses the organism's genetic material." data-term-url="/en/glossary/view/eukaryote/5297">eukaryotes</mark> is that prokaryotes have one main circular <mark class="term" data-term="chromosome" data-term-def="The organized genetic structure of DNA with associated proteins that contains the hereditary information necessary for reproduction, protein manufacture, and other functions." data-term-url="/en/glossary/view/chromosome/3760">chromosome</mark>, while eukaryotes typically have many linear chromosomes. When a prokaryote divides, it must copy its genetic material and separate the two copies between the two new <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> that result from the division, just like eukaryotes (Figure 5). However, the <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> is different. In prokaryotes, the circular chromosome is physically attached to a certain point of the inside of the plasma <mark class="term" data-term="membrane" data-term-def="A thin layer of tissue that forms a boundary of a cell or cell part." data-term-url="/en/glossary/view/membrane/8282">membrane</mark> of the cell. As the cell copies the chromosome in preparation for cell division, it attaches the new copy in a separate place. This way, the two copies of the chromosome are attached away from each other. Then, when the cell splits into two, the bacterium is careful to ensure that each of the two new cells will have one copy of the chromosome.</p> <div class="figure"> <figure> <button class="lightbox-button lightbox-button--icon" data-lightbox="" data-lightbox-src="/img/library/large_images/image_6591.jpg"> <img src="/img/library/modules/mid196/Image/VLObject-6591-131031121032.jpg" alt="Figure 5: Binary fission of bacterial cells" /> </button> <figcaption> <p><strong>Figure 5:</strong> Binary fission of bacterial cells</p> </figcaption> </figure> </div> <p>In the more complex <mark class="term" data-term="eukaryotic" data-term-def="Of cells with a nucleus and other organelles that are surrounded by lipid membranes" data-term-url="/en/glossary/view/eukaryotic/6539">eukaryotic</mark> <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>, the G<sub>1</sub>, S, and G<sub>2</sub> phases are collectively referred to as <em>interphase,</em> as these phases cannot be distinguished by just looking at the cells under the microscope. Even cells that are growing and dividing very quickly in our bodies spend approximately 78% of their lives in interphase. During interphase, eukaryotic cells double in size, synthesize new strands 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>, and prepare for <mark class="term" data-term="mitosis" data-term-def="Process occurring as part of the eukaryotic cell cycle. In mitosis, chromosomes in the cell nucleus separate into two identical chromosome&hellip;" data-term-url="/en/glossary/view/mitosis/10188">mitosis</mark> and <mark class="term" data-term="cytokinesis" data-term-def="The process of cell division in the eukaryotic cell cycle, characterized by the cytoplasm dividing to form two daughter cells." data-term-url="/en/glossary/view/cytokinesis/10178">cytokinesis</mark>. </p><p>Some <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>, like human skin cells, will enter the mitotic phase and divide frequently throughout life in order to accommodate changes in size as an <mark class="term" data-term="organism" data-term-def="Any connected living system, such as an animal, plant, fungus, or bacterium. Organisms may be composed of a single cell or&hellip;" data-term-url="/en/glossary/view/organism/2171">organism</mark> grows or to generate new cells to repair tissues damaged by illness or injuries. Other cells, like muscle, nerve, and red blood cells, will remain in a permanent G<sub>0</sub> phase without ever re-entering the mitotic phase. Even cells that are busy reproducing constantly throughout their lives spend very little time in the actual mitotic phase (M phase) as compared to the other phases of their life cycle (Alberts, et al., 2002). Figure 6 illustrates how the various phases compare in length.</p> <div class="figure"> <figure> <button class="lightbox-button lightbox-button--icon" data-lightbox="" data-lightbox-src="/img/library/large_images/image_6592.jpg"> <img src="/img/library/modules/mid196/Image/VLObject-6592-131031121042.jpg" alt="Figure 6: Relative lengths of the cell cycle phases" /> </button> <figcaption> <p><strong>Figure 6:</strong> Relative lengths of the cell cycle phases</p> </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 class="" name="cc6594"> <div class="form-entry"> <div class="form-entry__field"> <span class="form-entry__field__label">The process of cell division is more complex in __________ cells.</span> <div class="form-entry__option"> <div class="form-entry__option__radio" data-answer="correct"> <label> <input id="q1-6594-0-option-a" name="quiz-option-6594" type="radio" value="eukaryotic" > <span class="option__label"> <span class="screen-reader-only">a.</span> eukaryotic </span> </label> <span class="quiz__response" id="response-6594-0"> <strong>Correct!</strong> </span> </div> <div class="form-entry__option__radio" data-answer="incorrect"> <label> <input id="q1-6594-1-option-b" name="quiz-option-6594" type="radio" value="prokaryotic" > <span class="option__label"> <span class="screen-reader-only">b.</span> prokaryotic </span> </label> <span class="quiz__response" id="response-6594-1"> <strong>Incorrect.</strong> </span> </div> </div> </div> </div> </form> </div> </section> <section id="toc_3"> <h2>Experimenting with the cell cycle</h2><p>So what causes one <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> to linger in G<sub>0</sub> instead of launching into the phases of G<sub>1</sub> to S-phase, G<sub>2</sub> and on to mitosis? Arthur Pardee, an American biochemist working at Princeton University, was one of the first to examine that question. He experimented with live cultures of hamster cells to find what he called the "restriction point." Pardee hypothesized that there must be a single decision point in a cell's life cycle where a cell commits to one of two paths: one path that leads toward cell division and another that keeps the cell in a quiescent, or inactive, G<sub>0</sub> state (Figure 7). </p> <div class="figure"> <figure> <button class="lightbox-button lightbox-button--icon" data-lightbox="" data-lightbox-src="/img/library/large_images/image_6597.jpg"> <img src="/img/library/modules/mid196/Image/VLObject-6597-131120111107.jpg" alt="Figure 7: The restriction point, “R,” late in G1 phase" /> </button> <figcaption> <p><strong>Figure 7:</strong> The restriction point, “R,” late in G<sub>1</sub> phase</p> </figcaption> </figure> </div> <p>Pardee began by restricting the amount of <mark class="term" data-term="nutrient" data-term-def="A chemical substance (e.g., minerals, vitamins, proteins) that is needed by an organism to survive and grow. See also: macronutrient and micronutrient." data-term-url="/en/glossary/view/nutrient/7058">nutrients</mark> and <mark class="term" data-term="hormone" data-term-def="A chemical compound that is secreted from a gland directly into the blood that acts as a chemical messenger to tissues&hellip;" data-term-url="/en/glossary/view/hormone/10183">hormones</mark> available to the experimental cultures to see if he could stop the <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>' progress toward cell division. He did this by removing the cell growth signals at different time intervals. After the cycles were stopped, he attempted to restart the cycle by adding back the growth signals. Throughout these <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>, Pardee was careful to time each culture to see how long it took to reenter S-phase and <mark class="term" data-term="mitosis" data-term-def="Process occurring as part of the eukaryotic cell cycle. In mitosis, chromosomes in the cell nucleus separate into two identical chromosome&hellip;" data-term-url="/en/glossary/view/mitosis/10188">mitosis</mark>. </p><p>Pardee found that it made no difference at all as to when in the cycle he removed the growth signals. All of the samples took the same amount of time to re-enter <mark class="term" data-term="mitosis" data-term-def="Process occurring as part of the eukaryotic cell cycle. In mitosis, chromosomes in the cell nucleus separate into two identical chromosome&hellip;" data-term-url="/en/glossary/view/mitosis/10188">mitosis</mark>. This result led Pardee to conclude that all of the <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> must have ended up at the same point, regardless of where they were in their cycle when he first removed the growth factor. </p><p>Pardee called the point where the <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> halted the "restriction point," and he hypothesized that it functioned as a “point of no return.” In other words, if growth signals are present, cells will proceed forward, and once they pass the restriction point, they will complete their current cycle – even if you remove the growth signals. Some people still refer to this restriction point found in the G<sub>1</sub> phase of all mammalian cells as the "Pardee point." It is the point in the life cycle at which a cell either commits to a path toward division, or stops proliferation and enters the G<sub>0</sub> phase. Scientists later found another checkpoint at G<sub>2</sub> that halts cell division if <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> was not synthesized properly during S-phase. </p><p>Pardee published his results in 1974 (Pardee, 1973). At that same time, scientists at the University of Colorado Medical Center began experimenting with a special line of human cancer <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>, called HeLa cells, to see if they could get cells to go backward in the cell cycle or jump from one stage to another out of order. They used HeLa cells because they proliferated quickly and could be kept alive indefinitely in a laboratory setting. In 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">experiments</mark>, the team fused different HeLa cells together that were at different phases of the cell cycle. They wanted to see if they could “trick” a <mark class="term" data-term="nucleus" data-term-def="1. [Atomic] A tiny, dense positively charged mass at the heart of an atom. The nucleus is composed of protons and&hellip;" data-term-url="/en/glossary/view/nucleus/1526">nucleus</mark> in one phase of the cell cycle to enter another phase by fusing it with the <mark class="term" data-term="cytoplasm" data-term-def="A clear, water-based gel that contains enzymes, salts, and organic molecules. In eukaryotic cells, cytoplasm surrounds the nucleus and organelles. The&hellip;" data-term-url="/en/glossary/view/cytoplasm/2570">cytoplasm</mark> of a cell in a different phase.</p><p>What they found was very interesting. They found that when they fused a G<sub>1</sub> <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> together with an S-phase cell, the <mark class="term" data-term="nucleus" data-term-def="1. [Atomic] A tiny, dense positively charged mass at the heart of an atom. The nucleus is composed of protons and&hellip;" data-term-url="/en/glossary/view/nucleus/1526">nucleus</mark> of the G<sub>1</sub> cell quickly entered S-phase. They predicted that something in the <mark class="term" data-term="cytoplasm" data-term-def="A clear, water-based gel that contains enzymes, salts, and organic molecules. In eukaryotic cells, cytoplasm surrounds the nucleus and organelles. The&hellip;" data-term-url="/en/glossary/view/cytoplasm/2570">cytoplasm</mark> of the S phase cell caused the G<sub>1</sub> nucleus to begin <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="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> and enter S-phase. However, when they fused a G<sub>2</sub> cell with an S-phase cell, the G<sub>2</sub> nucleus would not enter S-phase. Because the G<sub>2</sub> nucleus had already duplicated its DNA, it would not enter another S-phase and re-duplicate its DNA.</p><p>Because the <mark class="term" data-term="nucleus" data-term-def="1. [Atomic] A tiny, dense positively charged mass at the heart of an atom. The nucleus is composed of protons and&hellip;" data-term-url="/en/glossary/view/nucleus/1526">nucleus</mark> could be tricked into moving forward in the cycle, but not backward, this clever <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> revealed that <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> can proceed through the cell cycle in only one direction. In addition, their results confirmed what many scientists had suspected – there are factors in the <mark class="term" data-term="cytoplasm" data-term-def="A clear, water-based gel that contains enzymes, salts, and organic molecules. In eukaryotic cells, cytoplasm surrounds the nucleus and organelles. The&hellip;" data-term-url="/en/glossary/view/cytoplasm/2570">cytoplasm</mark> of cells that control the progression through the phases of the cell cycle (Rao & Johnson, 1970). The hunt was on to find them.</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 class="" name="cc6595"> <div class="form-entry"> <div class="form-entry__field"> <span class="form-entry__field__label">What is the result of removing growth signals in a cell after it has passed the "restriction point"?</span> <div class="form-entry__option"> <div class="form-entry__option__radio" data-answer="incorrect"> <label> <input id="q1-6595-0-option-a" name="quiz-option-6595" type="radio" value="The cell will be unable to divide." > <span class="option__label"> <span class="screen-reader-only">a.</span> The cell will be unable to divide. </span> </label> <span class="quiz__response" id="response-6595-0"> <strong>Incorrect.</strong> </span> </div> <div class="form-entry__option__radio" data-answer="correct"> <label> <input id="q1-6595-1-option-b" name="quiz-option-6595" type="radio" value="The cell will complete its division cycle." > <span class="option__label"> <span class="screen-reader-only">b.</span> The cell will complete its division cycle. </span> </label> <span class="quiz__response" id="response-6595-1"> <strong>Correct!</strong> </span> </div> </div> </div> </div> </form> </div> </section> <section id="toc_4"> <h2>Controlling the cell cycle</h2><p>Several years after 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">experiments</mark> in Colorado, Tim Hunt, an English biochemist, began to look for the cellular factors that control <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 and other life cycle activities. He found his answers while conducting <mark class="term" data-term="research" data-term-def="A study or an investigation." data-term-url="/en/glossary/view/research/8257">research</mark> as a visiting professor at Woods Hole Oceanographic Institute in Massachusetts. </p><p>Hunt began by looking for a <mark class="term" data-term="protein" data-term-def="Macromolecules that are polymers of individual amino acids arranged in a chain and joined together by peptide bonds (and so also&hellip;" data-term-url="/en/glossary/view/protein/1594">protein</mark> that might be responsible for triggering the various stages 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. He got the idea from <mark class="term" data-term="research" data-term-def="A study or an investigation." data-term-url="/en/glossary/view/research/8257">research</mark> that showed cells would not enter the mitotic phase if treated with drugs that inhibit protein <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>. This meant that the cells had to make some new proteins in order to begin <mark class="term" data-term="mitosis" data-term-def="Process occurring as part of the eukaryotic cell cycle. In mitosis, chromosomes in the cell nucleus separate into two identical chromosome&hellip;" data-term-url="/en/glossary/view/mitosis/10188">mitosis</mark>. The question became, “What are these mitosis-causing proteins?” Proteins, however, cannot be seen under a microscope in the bustling <mark class="term" data-term="environment" data-term-def="The conditions that surround and affect an organism." data-term-url="/en/glossary/view/environment/8270">environment</mark> of living cells. So Hunt, like Flemming, had to be an innovator and adapt a tool from biochemistry, called radioactive tagging, for use in his <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>. </p><p>Hunt injected radioactive amino <mark class="term" data-term="acid" data-term-def="Generally, a substance that reacts with bases to form a salt, several different definitions of acids have been proposed by different&hellip;" data-term-url="/en/glossary/view/acid/1573">acids</mark> into sea urchin eggs (Figure 8) to help him “see” <mark class="term" data-term="protein" data-term-def="Macromolecules that are polymers of individual amino acids arranged in a chain and joined together by peptide bonds (and so also&hellip;" data-term-url="/en/glossary/view/protein/1594">proteins</mark> in much the same way that Flemming had used his dyes to highlight the <mark class="term" data-term="chromatin" data-term-def="Chromatin is the substance inside of the cell's nucleus and it consists of DNA, proteins (primarily histones), and chromosomal RNA. The&hellip;" data-term-url="/en/glossary/view/chromatin/9839">chromatin</mark> he wanted to see. As eggs used the radioactive <mark class="term" data-term="amino acid" data-term-def="Biochemical molecules that contain at least one amine group (-NH<sub>2</sub>) and at least one carboxylic acid group (-COOH) and conform&hellip;" data-term-url="/en/glossary/view/amino+acid/1596">amino acids</mark> to synthesize new proteins, the newly generated proteins would be <em>tagged</em> with <mark class="term" data-term="radioactivity" data-term-def="The spontaneous emission of radiation, due to a nuclear reaction or direct emission from an unstable atomic nucleus. Radioactivity takes&hellip;" data-term-url="/en/glossary/view/radioactivity/5301">radioactivity</mark> and visible when viewed with <mark class="term" data-term="X-ray" data-term-def="A form of electromagnetic radiation with higher frequency and energy than any other electromagnetic radiation besides gamma rays. X-rays have various&hellip;" data-term-url="/en/glossary/view/X~ray/7573">x-ray</mark> imaging devices.</p> <div class="figure"> <figure> <button class="lightbox-button lightbox-button--icon" data-lightbox="" data-lightbox-src="/img/library/large_images/image_6598.jpg"> <img src="/img/library/modules/mid196/Image/VLObject-6598-131120111119.jpg" alt="Figure 8: Eggs from sea urchins like this are often used in research because they are almost completely transparent." /> </button> <figcaption> <p><strong>Figure 8:</strong> Eggs from sea urchins like this are often used in research because they are almost completely transparent.</p> <span class="credit">image ©Wikimedia Commons</span> </figcaption> </figure> </div> <p>Using the bio-tagging technique, Hunt tracked the new <mark class="term" data-term="protein" data-term-def="Macromolecules that are polymers of individual amino acids arranged in a chain and joined together by peptide bonds (and so also&hellip;" data-term-url="/en/glossary/view/protein/1594">proteins</mark> as they developed in the sea urchin eggs over time and found that levels of one protein in particular would rise and fall at regular intervals as the <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> entered the mitotic phase. The levels would build dramatically just prior to <mark class="term" data-term="mitosis" data-term-def="Process occurring as part of the eukaryotic cell cycle. In mitosis, chromosomes in the cell nucleus separate into two identical chromosome&hellip;" data-term-url="/en/glossary/view/mitosis/10188">mitosis</mark> and then fall suddenly just prior to cell division. It seems that Hunt had found his mystery protein (Evans, et al., 1983).</p><p>Hunt called the <mark class="term" data-term="protein" data-term-def="Macromolecules that are polymers of individual amino acids arranged in a chain and joined together by peptide bonds (and so also&hellip;" data-term-url="/en/glossary/view/protein/1594">protein</mark> "cyclin" – one that we now know to be an integral part of the <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> cycle <mark class="term" data-term="control" data-term-def="In science, a control is a system for which the expected change or outcome is well known and is measured or&hellip;" data-term-url="/en/glossary/view/control/3801">control</mark> <mark class="term" data-term="system" data-term-def="A group of interacting, interrelated or interdependent components that form a complex whole. The size of the system is defined for&hellip;" data-term-url="/en/glossary/view/system/3904">system</mark>. Cyclins <mark class="term" data-term="work" data-term-def="A process that occurs when a force acts over a distance, as when an object is moved. Work equals the multiple&hellip;" data-term-url="/en/glossary/view/work/1502">work</mark> in tandem with a family of <mark class="term" data-term="enzyme" data-term-def="Molecules produced by living organisms that help catalyze biochemical reactions. Enzymes are predominantly protein or protein-based molecules and are highly&hellip;" data-term-url="/en/glossary/view/enzyme/1595">enzymes</mark> called <em>kinases</em> to control the cell cycle. These kinases are found in a cell's <mark class="term" data-term="cytoplasm" data-term-def="A clear, water-based gel that contains enzymes, salts, and organic molecules. In eukaryotic cells, cytoplasm surrounds the nucleus and organelles. The&hellip;" data-term-url="/en/glossary/view/cytoplasm/2570">cytoplasm</mark>; but unlike cyclins, kinases do not build up and disappear over time. The cell cycle kinases exist at relatively constant levels in a dormant state in a cell's cytoplasm until they are activated by cyclins. When activated, these <em>cyclin-dependent kinases,</em> or CDKs, trigger the chain <mark class="term" data-term="reaction" data-term-def="A chemical change when substances come into contact with each other." data-term-url="/en/glossary/view/reaction/8263">reactions</mark> that initiate <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> replication, <mark class="term" data-term="mitosis" data-term-def="Process occurring as part of the eukaryotic cell cycle. In mitosis, chromosomes in the cell nucleus separate into two identical chromosome&hellip;" data-term-url="/en/glossary/view/mitosis/10188">mitosis</mark>, and other events in the life cycle of a cell.</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 class="" name="cc6596"> <div class="form-entry"> <div class="form-entry__field"> <span class="form-entry__field__label">Hunt injected radioactive amino acids into sea urchin eggs in order to see</span> <div class="form-entry__option"> <div class="form-entry__option__radio" data-answer="correct"> <label> <input id="q1-6596-0-option-a" name="quiz-option-6596" type="radio" value="proteins." > <span class="option__label"> <span class="screen-reader-only">a.</span> proteins. </span> </label> <span class="quiz__response" id="response-6596-0"> <strong>Correct!</strong> </span> </div> <div class="form-entry__option__radio" data-answer="incorrect"> <label> <input id="q1-6596-1-option-b" name="quiz-option-6596" type="radio" value="mitosis." > <span class="option__label"> <span class="screen-reader-only">b.</span> mitosis. </span> </label> <span class="quiz__response" id="response-6596-1"> <strong>Incorrect.</strong> </span> </div> </div> </div> </div> </form> </div> </section> <section id="toc_5"> <h2>Checkpoints in the cell cycle</h2><p>Although it is the cyclins and CDKs that manage when <mark class="term" data-term="eukaryotic" data-term-def="Of cells with a nucleus and other organelles that are surrounded by lipid membranes" data-term-url="/en/glossary/view/eukaryotic/6539">eukaryotic</mark> <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> enter each phase, the <mark class="term" data-term="system" data-term-def="A group of interacting, interrelated or interdependent components that form a complex whole. The size of the system is defined for&hellip;" data-term-url="/en/glossary/view/system/3904">system</mark> relies on checkpoints like the one discovered by Pardee to ensure that all systems are ready before launching into the most critical phases of the cycle – <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="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>, and following that, <mark class="term" data-term="mitosis" data-term-def="Process occurring as part of the eukaryotic cell cycle. In mitosis, chromosomes in the cell nucleus separate into two identical chromosome&hellip;" data-term-url="/en/glossary/view/mitosis/10188">mitosis</mark>. The cell cycle control system keeps the life cycle moving forward in an orderly manner, sort of like the mechanical timer on a washing machine ensures that clothes are washed, rinsed, and spun dry in the correct order. The cell cycle control system, like a washing machine timer, is automatic, unidirectional, and dependent on signal inputs at certain checkpoints to keep the <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> moving forward (Figure 9).</p> <div class="figure"> <figure> <button class="lightbox-button lightbox-button--icon" data-lightbox=""> <img src="/img/library/modules/mid196/Image/VLObject-6593-131031121052.jpg" alt="Figure 9: Checkpoints ensure that the cell cycle can be halted if damage or errors are detected." /> </button> <figcaption> <p><strong>Figure 9:</strong> Checkpoints ensure that the cell cycle can be halted if damage or errors are detected.</p> </figcaption> </figure> </div> <p>Tim Hunt, who discovered the cyclins, won the <mark class="term" data-term="Nobel Prize" data-term-def="Awards made annually, beginning in 1901, from funds originally established by Alfred B. Nobel for outstanding achievement in physics, chemistry, medicine&hellip;" data-term-url="/en/glossary/view/Nobel+Prize/3843">Nobel Prize</mark> in medicine 2001, together with Paul Nurse, who discovered the cyclin-dependent kinases (CDKs). They also shared the prize with Leland Hartwell, who pioneered the <mark class="term" data-term="research" data-term-def="A study or an investigation." data-term-url="/en/glossary/view/research/8257">research</mark> into the checkpoints of the <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> cycle.</p><p>The <mark class="term" data-term="network" data-term-def="An interconnected system; an interrelated net-like arrangement of parts." data-term-url="/en/glossary/view/network/8740">network</mark> of <mark class="term" data-term="protein" data-term-def="Macromolecules that are polymers of individual amino acids arranged in a chain and joined together by peptide bonds (and so also&hellip;" data-term-url="/en/glossary/view/protein/1594">proteins</mark> that make up the <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> cycle control <mark class="term" data-term="system" data-term-def="A group of interacting, interrelated or interdependent components that form a complex whole. The size of the system is defined for&hellip;" data-term-url="/en/glossary/view/system/3904">system</mark> manage an extremely complex series of operations that allow the cells in our bodies – and those in all the plants and animals around us – to grow and sustain life. From the careful replication 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> that becomes the <mark class="term" data-term="blueprint" data-term-def="A detailed outline or plan of action. The word technically refers to a process of photographic printing, used chiefly in copying&hellip;" data-term-url="/en/glossary/view/blueprint/5295">blueprint</mark> of life for new <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 to the final cleave that pinches one cell into two during <mark class="term" data-term="cytokinesis" data-term-def="The process of cell division in the eukaryotic cell cycle, characterized by the cytoplasm dividing to form two daughter cells." data-term-url="/en/glossary/view/cytokinesis/10178">cytokinesis</mark>, every phase must go off without a hitch – millions and millions of times during the life of an <mark class="term" data-term="organism" data-term-def="Any connected living system, such as an animal, plant, fungus, or bacterium. Organisms may be composed of a single cell or&hellip;" data-term-url="/en/glossary/view/organism/2171">organism</mark>. Most the time the <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> goes smoothly. However, occasionally errors occur or the cell cycle control systems get damaged. When this happens, the result can be disastrous for the cell and can even lead to cancer. In fact, because the main feature of a cancer cell is constant unrestrained growth, cancer is often referred to as a disease of the cell cycle. </p> </div> </section> <hr class="border-color-dark" /> <footer class="module__footer"> <p class="citation"> <em> Nathan H Lents, Ph.D., Donna Hesterman “Cell Division I” Visionlearning Vol. BIO-3 (5), 2013. </em> </p>  <div class="title-list" id="refs" name="refs"> <p class="h6 title-list__title"> References </p> <ul class="title-list__list"> <li>Alberts. B., Johnson, A., Lewis, J., et al. (2002). <em>Molecular Biology of the Cell,</em> 4th edition. New York: Garland Science; Accessed online at http://www.ncbi.nlm.nih.gov/books/NBK26824/ on March 20, 2013.</li> <li>Campbell, Neal A., & Reece, Jane B. (2005). <em>Biology</em>, seventh edition. Pearson Benjamin Cummings.</li> <li>Evans, T., Rosenthal, E., Youngblom, J., Distel D., & Hunt, T. (1983). Cyclin: a protein specified by maternal mRNA in sea urchin eggs that is destroyed at each cleavage division. <em>Cell, 2,</em> 289-386.</li> <li>Flemming, W. (1878). Kiel. Zur Kenntniss der Zelle und ihrer Theilungs-Erscheinungen. Accessed online at: http://www.schriften.uni-kiel.de/Band%203/Flemming%20(23-27).pdf March 20, 2013.</li> <li>Jackson, Peter K. (2008). The Hunt for Cyclin. <em>Cell, 134,</em> 199-202. http://www.uam.es/personal_pdi/ciencias/jmsierra/documents/Jackson2008Cell.pdf.</li> <li>Pardee, A. (1973). A Restriction Point for Control of Normal Animal Cell Proliferation. <em>Proceedings of the National Academy of Sciences, 71,</em> 1286-1290.</li> <li>Rao, P. & Johnson, R. (1970). Mammalian cell fusion: Studies on the regulation of DNA synthesis and mitosis. <em>Nature, 224,</em> 159-164.</li> <li>Zacharias, Helmut. Famous scholars from Kiel. Accessed online at http://www.uni-kiel.de/grosse-forscher/index.php?nid=flemming&lang=e</li> </ul> </div> </footer> </div>   </div>  <div class="order-1 order-2--lg module__tools"> <div class="narrow margin-x-auto position-sticky-top font-size-md"> <div class="padding-2 border-radius box-shadow-1--lg"> <div class="tabs" role="tablist"> <nav> <button class="button button--icon-label" id="tab-button-in-this-module" aria-label="Table of Contents" aria-controls="tab-panel-module__tools" aria-selected="true" role="tab"> <span class="icon icon-list" aria-hidden="true"></span> <span class="button__text">Contents</span> </button> <button class="button button--icon-label" id="tab-button-toggle-terms" aria-controls="tab-panel-toggle-terms" aria-selected="false" role="tab"> <span class="icon icon-glossary-highlight"></span> <span class="button__text">Glossary Terms</span> </button> </nav> <hr class="divider" /> <div class="tabs__panel shown" id="tab-panel-module__tools" aria-labelledby="tab-button-module__tools" role="tabpanel"> <p class="font-weight-bold margin-bottom-1"> Table of Contents </p> <div class="table-of-contents" id="module-toc"> <ul> <li><a href="/en/library/biology/2/cell-division-i/196#toc_1">The discovery of cell division</a> </li> <li><a href="/en/library/biology/2/cell-division-i/196#toc_2">Cell life cycles</a> </li> <li><a href="/en/library/biology/2/cell-division-i/196#toc_3">Experimenting with the cell cycle</a> </li> <li><a href="/en/library/biology/2/cell-division-i/196#toc_4">Controlling the cell cycle</a> </li> <li><a href="/en/library/biology/2/cell-division-i/196#toc_5">Checkpoints in the cell cycle</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. 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Cell Division I | Biology | Visionlearning