Membranes II | Biology | Visionlearning

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It highlights the importance of the study of cell membranes by looking at advances in treating cystic fibrosis and common digestive ailments as well as the development of effective pain relievers."> <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/membranes-ii/204" }, "name": "Membranes II", "headline": "Membranes II: Passive and active transporters", "author": { "@type": "Person", "name": "Nathan H Lents, Ph.D." }, "datePublished": "2014-11-04 14:41:27", "dateModified": "2017-02-12T08:30:00+05:00", "image": { "@type": "ImageObject", "url": "/img/library/moduleImages/featured_image_204-23061209062709.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": "For living things to survive, different molecules need to enter and leave cells, yet cell membranes serve as a barrier to most molecules. Fortunately, all living cells have built-in transporters that allow water, glucose, sodium, potassium, chloride, and other molecules to cross the plasma membrane. This module looks at how passive and active transporters work. 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Control Earth's Temperature</a></li> <li><a href="/en/library/earth-science/6/circulation-in-the-atmosphere/255">Circulation in the Atmosphere</a></li> </ul> </div> <button class="accordion__button" id="acc-button-hazards" data-accordion="button" aria-controls="acc-panel-hazards" aria-expanded="false"> <span class="accordion__button__label"> Hazards </span> </button> <div class="accordion__panel" id="acc-panel-hazards" data-accordion="panel" aria-labelledby="acc-button-hazards" role="region"> <ul class="nav text-color-link"> <li><a 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" 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</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><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 class="current">Membranes II</li> <li><a href="/en/library/biology/2/cellular-organelles-i/195">Cellular Organelles I</a></li> <li><a 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class="module__header"> <span class="subcategory"> <strong><em>Cell Biology</em></strong> </span> <h1>Membranes II: <sub><em>Passive and active transporters</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/biology/2/membranes-ii/204/reading" class="is-active" aria-current="page" >Reading</a> </li> <li> <a href="/en/library/biology/2/membranes-ii/204/quiz" >Quiz</a> </li> <li> <a href="/en/library/biology/2/membranes-ii/204/resources" >Teach with this</a> </li> </ul> </nav> <script type="application/ld+json"> { "@context": "http://schema.org", "@type": "AudioObject", "contentUrl": "https://www.visionlearning.com/img/library/moduleAudio/module_204.mp3", "description": "Recording of Membranes II : For living things to survive, different molecules need to enter and leave cells, yet cell membranes serve as a barrier to most molecules. Fortunately, all living cells have built-in transporters that allow water, glucose, sodium, potassium, chloride, and other molecules to cross the plasma membrane. This module looks at how passive and active transporters work. It highlights the importance of the study of cell membranes by looking at advances in treating cystic fibrosis and common digestive ailments as well as the development of effective pain relievers.", "encodingFormat": "mp3", "name": "module_204.mp3" } </script> <div class="module__audio"> <div class="audio-player border border-radius"> <audio id="audio"> <source src="https://www.visionlearning.com/img/library/moduleAudio/module_204.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> <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/biology/2/membranes-ii/204#toc_1">The plasma membrane: A selective barrier</a> </li> <li><a href="/en/library/biology/2/membranes-ii/204#toc_2">Passive and active transporters</a> </li> <li><a href="/en/library/biology/2/membranes-ii/204#toc_3">Channels: Passive transporters</a> </li> <li><a href="/en/library/biology/2/membranes-ii/204#toc_4">Some channels have gates</a> </li> <li><a href="/en/library/biology/2/membranes-ii/204#toc_5">Pumps: Active transporters</a> </li> <li><a href="/en/library/biology/2/membranes-ii/204#toc_6">The sodium/potassium pump</a> </li> <li><a href="/en/library/biology/2/membranes-ii/204#toc_7">Discovery of the Na+/K+ pump</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 the absence of one tiny amino acid in cell membranes causes Cystic Fibrosis, a life-threatening disease? And a common aliment, heartburn, is treated with medicine that slows down the rate at which protons are pumped across cell membranes into the stomach. Studying how molecules travel across plasma membranes (cell membranes) is the key to understanding and treating many medical conditions.</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>Whether or not a molecule is able to pass easily, or at all, into or out of a cell is largely dependent on its charge and solubility in water.</p></li> <li><p>The plasma membrane serves as a semi-permeable barrier to the cell. Only uncharged, non-polar molecules are able to pass into or out of the cell without aid.</p></li> <li><p>All plasma membranes possess transporters to help move molecules from one side of the membrane to the other. These transporters can be active (pumps) or passive (channels) and are sometimes regulated by gates.</p></li> <li><p>The lack of a specific transporter can interrupt cellular functions and cause diseases like cystic fibrosis.</p></li> <li><p>Research into pain relievers provided insight into the most important and universal transporter in the human body, the sodium-potassium pump.</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>barrier </dt> <dd> something that prevents passage; an obstruction that does not allow movement from one area to another </dd> <dt>gradient </dt> <dd> an upward or downward slope; the degree of incline or descent </dd> <dt><a href="/en/glossary/view/membrane">membrane </a></dt> <dd> a thin layer of tissue</dd> </dl> </div> </div> </div> <section> <p>Approximately 30,000 Americans have a disease called Cystic Fibrosis (CF). This is a genetic disease that an individual inherits from both parents and suffers from throughout their lives. People with CF have serious respiratory and digestive problems because they build up a <mark class="term" data-term="viscosity" data-term-url="/en/glossary/view/viscosity" data-term-def="The measurement of a fluid's resistance to shear or flow. Highly viscous fluids resist motion due to their molecular composition that&hellip;">viscous</mark>, sticky mucous in their lungs and other organs. Just a couple of decades ago, most individuals with CF did not survive long enough to begin kindergarten. Fortunately, medical <mark class="term" data-term="research" data-term-def="A study or an investigation." data-term-url="/en/glossary/view/research/8257">research</mark> has pushed the average lifespan of a CF sufferer to approximately 35 years. In addition, the root cause of the disease has been identified: 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">membranes</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">cells</mark> in the affected organs are missing a key component and so do not function properly.</p> <p>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> (also called 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> membrane) is anything but a simple barrier between the inside of a cell and the <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> outside of it. As explored in <a href="/en/library/Biology/2/Membranes-I/198">Membranes I: Introduction to Biological Membranes</a>, there is a wide variety of embedded components that are essential to the life of the cell, including <mark class="term" data-term="lipids" data-term-def="A diverse group of organic molecules that contain long hydrocarbon chains or rings and are hydrophobic. Examples are fats, oils, waxes,&hellip;" data-term-url="/en/glossary/view/lipids/1599">lipids</mark>, carbohydrates, and <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> – many of which regulate what is allowed to pass into and out of the cell (Figure 1).</p>  <div class="figure"> <figure> <button class="lightbox-button" data-lightbox-src="/img/library/large_images/image_6701.jpg" data-lightbox="image"> <img src="/img/library/modules/mid204/Image/VLObject-6701-140516030545.jpg" alt="Figure 1: Many types of components are mingled throughout the cell membrane." /> </button> <figcaption> <p><strong>Figure 1:</strong> Many types of components are mingled throughout the cell membrane.</p> </figcaption> </figure> </div> <p><section id="toc_1" class=""> <h2>The plasma membrane: A selective barrier</h2></p> <p>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 all <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> is a barrier to most <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>. Only uncharged, non-polar molecules can easily pass through the membrane. Non-polar molecules are those whose <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> involve equal or symmetrical sharing of <mark class="term" data-term="electron" data-term-def="A subatomic particle with a negative charge of 1.60 × 10<sup>-19</sup> coulombs and a mass of 9.11 × 10<sup>-31</sup> kg. Electrons&hellip;" data-term-url="/en/glossary/view/electron/852">electrons</mark> so there are no partial positive or negative <mark class="term" data-term="charge" data-term-def="A quantity of electricity." data-term-url="/en/glossary/view/charge/8258">charges</mark>. This includes gases like carbon dioxide and oxygen and a few lipid <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> like testosterone and estrogen.</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> <p>However, most <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> in our bodies are either charged or <mark class="term" data-term="polar" data-term-def="Carrying an electrical charge." data-term-url="/en/glossary/view/polar/8730">polar</mark>. For example, water cannot pass directly through a biological <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> because it is a <mark class="term" data-term="polar molecule" data-term-def="Refer to polar covalent molecule." data-term-url="/en/glossary/view/polar+molecule/2568">polar molecule</mark>, with partial positive and partial negative <mark class="term" data-term="charge" data-term-def="A quantity of electricity." data-term-url="/en/glossary/view/charge/8258">charges</mark>. The interior environment of the <mark class="term" data-term="plasma membrane" data-term-def="The semi-permeable layer of tissue enclosing the cytoplasm of a cell. The plasma membrane separates and protects the cell's interior from&hellip;" data-term-url="/en/glossary/view/plasma+membrane/5282">plasma membrane</mark> is highly <mark class="term" data-term="hydrophobic" data-term-def="Literally meaning "water fearing," a substance that has little affinity for water. Generally, non-polar molecules that do not dissolve in&hellip;" data-term-url="/en/glossary/view/hydrophobic/1600">hydrophobic</mark> because of the close crowding of all of the fatty acid <mark class="term" data-term="hydrocarbon" data-term-def="An organic compound that contains only hydrogen and carbon." data-term-url="/en/glossary/view/hydrocarbon/1585">hydrocarbon</mark> tails (see <a href="/en/library/Biology/2/Membranes-I/198">Membranes I: Introduction to Biological Membranes</a>). Those hydrocarbon tails are filled with non-polar <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>, and there are essentially zero polar bonds anywhere in the interior section of the membrane. This creates a very hydrophobic environment, and thus water is strongly repelled.</p><p>Glucose is another example of a <mark class="term" data-term="polar" data-term-def="Carrying an electrical charge." data-term-url="/en/glossary/view/polar/8730">polar</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">molecule</mark> that cannot easily pass through the <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>. It is much larger than water with many polar <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> all throughout the molecule. <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>, such as sodium (Na<sup>+</sup>) and chloride (Cl<sup>-</sup>), have an even more difficult time going through the membrane than <mark class="term" data-term="glucose" data-term-def="The primary form of sugar stored in the human body for energy: C<sub>6</sub>H<sub>12</sub>O<sub>6</sub>." data-term-url="/en/glossary/view/glucose/8735">glucose</mark>. They are not just partially charged; they are <em>fully</em> charged and thus strongly repelled by the interior of the membrane (see Figure 2).</p>  <div class="figure"> <figure> <button class="lightbox-button" data-lightbox-src="/img/library/large_images/image_7195.jpg" data-lightbox="image"> <img src="/img/library/modules/mid204/Image/VLObject-7195-141027021012.jpg" alt="Figure 2: Non-polar molecules like oxygen and nitrogen diffuse through a membrane, whereas polar molecules and charged ions do not diffuse through a membrane." /> </button> <figcaption> <p><strong>Figure 2</strong>: Non-polar molecules like oxygen and nitrogen diffuse through a membrane, whereas polar molecules and charged ions do not diffuse through a membrane.</p> <span class="credit">image ©Visionlearning</span> </figcaption> </figure> </div> <p>However, we also know that water, <mark class="term" data-term="glucose" data-term-def="The primary form of sugar stored in the human body for energy: C<sub>6</sub>H<sub>12</sub>O<sub>6</sub>." data-term-url="/en/glossary/view/glucose/8735">glucose</mark>, sodium, and chloride move in and out 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> all the time, which means that there must be something that assists them. This “something” is a collection of <em>transporters</em>: both passive and active.</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="cc7090"> <div class="form-entry"> <div class="form-entry__field"> <span class="form-entry__field__label">It is more difficult for molecules to pass through cell membranes when they</span> <div class="form-entry__option"> <div class="form-entry__option__radio" data-answer="correct"> <label> <input id="q1-7090-0-option-a" name="quiz-option-7090" type="radio" value="carry a charge" > <span class="option__label"> <span class="screen-reader-only">a.</span> carry a charge </span> </label> <span class="quiz__response" id="response-7090-0"> <strong>Correct!</strong> </span> </div> <div class="form-entry__option__radio" data-answer="incorrect"> <label> <input id="q1-7090-1-option-b" name="quiz-option-7090" type="radio" value="do not carry a charge" > <span class="option__label"> <span class="screen-reader-only">b.</span> do not carry a charge </span> </label> <span class="quiz__response" id="response-7090-1"> <strong>Incorrect.</strong> </span> </div> </div> </div> </div> </form> </div> </section> <section id="toc_2"> <h2>Passive and active transporters</h2><p>There are transporters embedded in every <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> <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> that allow <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> to pass through. In <a href="/en/library/Biology/2/Membranes-I/198">Membranes I</a>, we discussed the water transporter, aquaporin – but there are many more of these transporters within the membranes of all living cells.</p><p>Transporters are <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 are divided into two classes: passive transporters, also called <em>channels</em>, and active transporters, also called <em>pumps</em>. The difference between active and passive transport is whether or not <mark class="term" data-term="energy" data-term-def="An abstract property defined as the capacity to do work. The basic forms of energy include chemical, electrical, mechanical, nuclear, and&hellip;" data-term-url="/en/glossary/view/energy/1497">energy</mark> is required to move 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">molecule</mark> from one side of the <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> to the other. A channel is <em>passive</em> because it does not require energy to help molecules flow through it. (The aquaporin water transporter is a channel.) Pumps, on the other hand, <em>do</em> require energy to do their work, so they are called <em>active transporters</em>.</p></section> <section id="toc_3"> <h2>Channels: Passive transporters</h2><p>In order to function, the heart, nerves, and muscles in a body need to move sodium <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> into and out of their <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>. However, because sodium <mark class="term" data-term="ion" data-term-url="/en/glossary/view/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;">ions</mark> are charged and cannot get through the <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> directly, cells have a sodium channel that creates a path – a tunnel – through the membrane where ions can flow freely.</p><p>Because channels merely provide a path for <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> to flow, they are only capable of allowing those molecules to flow from where they are in high <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> to where they are in low concentration. In other words, channels allow specific molecules to <mark class="term" data-term="diffusion" data-term-url="/en/glossary/view/diffusion" data-term-def="The movement of atoms or molecules from one part of a medium to another caused by their random thermal motion.&hellip;">diffuse</mark> when they otherwise couldn't because a <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> is in their way. When a channel helps molecules to move through a membrane, this is called "facilitated <mark class="term" data-term="diffusion" data-term-def="The movement of atoms or molecules from one part of a medium to another caused by their random thermal motion.&hellip;" data-term-url="/en/glossary/view/diffusion/2690">diffusion</mark>." The molecules are passively spreading out evenly, but they are getting a little help from the channels to do so (see Figure 3). </p>  <div class="figure"> <figure> <button class="lightbox-button" data-lightbox-src="/img/library/large_images/image_7131.jpg" data-lightbox="image"> <img src="/img/library/modules/mid204/Image/VLObject-7131-140910010902.jpg" alt="Figure 3: Regular (the fat soluble molecules) and facilitated (the water soluble molecules) diffusion." /> </button> <figcaption> <p><strong>Figure 3</strong>: Regular (the fat soluble molecules) and facilitated (the water soluble molecules) diffusion.</p> <span class="credit">image ©BruceBlaus</span> </figcaption> </figure> </div> <p>For example, inside of human <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>, there is a fairly low <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 sodium <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>, but outside of the cells, in the general <mark class="term" data-term="fluid" data-term-def="Able to flow because the intermolecular forces allow the molecules to move around in relation to one another. Both liquids and&hellip;" data-term-url="/en/glossary/view/fluid/8724">fluids</mark> of the body, there is a high concentration of sodium <mark class="term" data-term="ion" data-term-url="/en/glossary/view/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;">ions</mark>. This is why tears, sweat, and other body fluids taste salty. Thus, surrounding every cell of your body, there is a <mark class="term" data-term="concentration gradient" data-term-def="The difference in molecule concentration inside and outside of the cell across a cell membrane." data-term-url="/en/glossary/view/concentration+gradient/7377">concentration gradient</mark> of sodium ions – low sodium inside of the cells and high sodium in the surrounding fluid. Channels can allow only the passive flow of <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> down their gradient (from high to low), not the other direction, so a sodium channel would allow sodium ions to flow into the cell, not out of it.</p><p>Channels are important for many different types of <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>. In 1989, it was discovered that the basis of Cystic Fibrosis was the lack of a specific kind of passive transport channel in 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> <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">membranes</mark> of CF patients. This channel, known as CFTR (<u>C</u>ystic <u>F</u>ibrosis <u>T</u>rans-membrane Conductance <u>R</u>egulator), is actually made in the cells of individuals with CF, but it lacks just one tiny piece: an 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">acid</mark> in a crucial location. Because of this one tiny alteration in its structure, CFTR is never delivered to the <mark class="term" data-term="plasma membrane" data-term-def="The semi-permeable layer of tissue enclosing the cytoplasm of a cell. The plasma membrane separates and protects the cell's interior from&hellip;" data-term-url="/en/glossary/view/plasma+membrane/5282">plasma membrane</mark> where it would normally allow chloride <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> to flow out of the cell (Cheng, et al., 1990). A CFTR channel is shown in Figure 4.</p>  <div class="figure"> <figure> <button class="lightbox-button" data-lightbox-src="/img/library/large_images/image_7196.jpg" data-lightbox="image"> <img src="/img/library/modules/mid204/Image/VLObject-7196-141027021016.jpg" alt="Figure 4: A CFTR channel." /> </button> <figcaption> <p><strong>Figure 4</strong>: A CFTR channel.</p> <span class="credit">image ©Visionlearning</span> </figcaption> </figure> </div> <p>The flow of chloride <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> from certain <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 the lungs is essential for making mucus of the proper consistency. Without chloride, the mucus is not as watery as it should be. When chloride fails to flow out from the cells of CF patients, <mark class="term" data-term="viscosity" data-term-url="/en/glossary/view/viscosity" data-term-def="The measurement of a fluid's resistance to shear or flow. Highly viscous fluids resist motion due to their molecular composition that&hellip;">viscous</mark> mucous builds up in their lungs, leading to the symptoms and infections associated with CF, such as frequent coughing and wheezing. This underscores how important a job the cell <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> plays. It is much more than a static, selective barrier.</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="cc7100"> <div class="form-entry"> <div class="form-entry__field"> <span class="form-entry__field__label">Channels allow molecules to</span> <div class="form-entry__option"> <div class="form-entry__option__radio" data-answer="correct"> <label> <input id="q1-7100-0-option-a" name="quiz-option-7100" type="radio" value="flow down their concentration gradient." > <span class="option__label"> <span class="screen-reader-only">a.</span> flow down their concentration gradient. </span> </label> <span class="quiz__response" id="response-7100-0"> <strong>Correct!</strong> </span> </div> <div class="form-entry__option__radio" data-answer="incorrect"> <label> <input id="q1-7100-1-option-b" name="quiz-option-7100" type="radio" value="be pumped from an area of lower concentration to an area of higher concentration." > <span class="option__label"> <span class="screen-reader-only">b.</span> be pumped from an area of lower concentration to an area of higher concentration. </span> </label> <span class="quiz__response" id="response-7100-1"> <strong>Incorrect.</strong> </span> </div> </div> </div> </div> </form> </div> </section> <section id="toc_4"> <h2>Some channels have gates</h2><p>Many <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>, especially neurons and muscle cells, have sodium channels on them, but these are usually held closed by <mark class="term" data-term="gate" data-term-def="Active ion channels can regulate the passage of ions via a gate mechanism. Gates can open (allow ions to flow&hellip;" data-term-url="/en/glossary/view/gate/7378">gates</mark>. These gates prevent sodium from rushing into the cell so that the gradient can be maintained. However, these gates can also be opened at specific times. Because sodium <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> is higher outside the cell than inside, if the gates on the sodium channel suddenly opened, sodium <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> would begin to flow inward.</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> <p>It is important to remember that <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> move in random paths. While molecules will flow in through the channels from outside 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>, some will also flow back out. It’s just that <em>more</em> <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> will flow into the cell than out of the cell because there are more <mark class="term" data-term="ion" data-term-url="/en/glossary/view/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;">ions</mark> outside to start with. Thus, when the <mark class="term" data-term="gate" data-term-def="Active ion channels can regulate the passage of ions via a gate mechanism. Gates can open (allow ions to flow&hellip;" data-term-url="/en/glossary/view/gate/7378">gates</mark> open, we say that there is <mark class="term" data-term="Net movement" data-term-def="Net movement occurs when molecules move from a region of higher concentration to a region of lower concentration due to random&hellip;" data-term-url="/en/glossary/view/Net+movement/7379">net movement</mark> of sodium ions into the cell. If the gates were to stay open long enough, the <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 sodium inside and outside would equal out. There would be no more gradient and no more net movement. This doesn’t actually happen, though, because the gates only open for a brief instant. </p></section> <section id="toc_5"> <h2>Pumps: Active transporters</h2><p>How do sodium <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> get to be at a high <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> outside 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> in the first place? To answer this, we must consider the topic of <mark class="term" data-term="active transport" data-term-def="The opposite of passive transport, active transport involves the input of energy (usually in the form of ATP), the building of&hellip;" data-term-url="/en/glossary/view/active+transport/7380">active transport</mark>. Active transport is exactly the opposite of passive transport. First, it <em>does</em> require the input of <mark class="term" data-term="energy" data-term-def="An abstract property defined as the capacity to do work. The basic forms of energy include chemical, electrical, mechanical, nuclear, and&hellip;" data-term-url="/en/glossary/view/energy/1497">energy</mark>, rather than relying on the random motion of <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> (and this usually comes in the form of ATP). Second, active transport <em>builds</em> <mark class="term" data-term="concentration gradient" data-term-def="The difference in molecule concentration inside and outside of the cell across a cell membrane." data-term-url="/en/glossary/view/concentration+gradient/7377">concentration gradients</mark> – meaning that it increases the concentration of molecules in a given area – rather than reducing them (see our <a href="/library/module_viewer.php?mid=216">Diffusion I: An Introduction</a> module). Third, it requires the action of a <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> pump (instead of a channel) to move molecules from one side of the membrane to the other.</p><p>Membrane pumps are <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> embedded in 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> that pump specific <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> or <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> into or out 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>. For example, there are <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">proton</mark> (H<sup>+</sup>) pumps in the lining of the stomach. They pump protons into the stomach cavity, creating a very acidic <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> to help digest food (Figure 5). People who suffer from chronic heartburn or indigestion might take Nexium, Prilosec, or Prevacid to treat this discomfort. These drugs work by slowing down the proton pumps in the stomach walls and thus making the stomach less acidic (Peghini et al., 1998). Other examples of pumps are the calcium (Ca<sup>2+</sup>) pumps in the intestines that help <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> calcium from food, and the <mark class="term" data-term="glucose" data-term-def="The primary form of sugar stored in the human body for energy: C<sub>6</sub>H<sub>12</sub>O<sub>6</sub>." data-term-url="/en/glossary/view/glucose/8735">glucose</mark> pumps in the kidney that grab all the glucose out of the pre-urine <mark class="term" data-term="fluid" data-term-def="Able to flow because the intermolecular forces allow the molecules to move around in relation to one another. Both liquids and&hellip;" data-term-url="/en/glossary/view/fluid/8724">fluid</mark> so that we don’t lose glucose constantly in our urine. Unlike channels, all of these pumps must use <mark class="term" data-term="energy" data-term-def="An abstract property defined as the capacity to do work. The basic forms of energy include chemical, electrical, mechanical, nuclear, and&hellip;" data-term-url="/en/glossary/view/energy/1497">energy</mark> to do this pumping.</p>  <div class="figure"> <figure> <button class="lightbox-button" data-lightbox-src="/img/library/large_images/image_7197.jpg" data-lightbox="image"> <img src="/img/library/modules/mid204/Image/VLObject-7197-141027021020.jpg" alt="Figure 5: A proton pump in the lining of the stomach." /> </button> <figcaption> <p><strong>Figure 5</strong>: A proton pump in the lining of the stomach.</p> <span class="credit">image ©Visionlearning</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="cc7107"> <div class="form-entry"> <div class="form-entry__field"> <span class="form-entry__field__label">The random motion of molecules is associated with _____________ transport.</span> <div class="form-entry__option"> <div class="form-entry__option__radio" data-answer="incorrect"> <label> <input id="q1-7107-0-option-a" name="quiz-option-7107" type="radio" value="active" > <span class="option__label"> <span class="screen-reader-only">a.</span> active </span> </label> <span class="quiz__response" id="response-7107-0"> <strong>Incorrect.</strong> </span> </div> <div class="form-entry__option__radio" data-answer="correct"> <label> <input id="q1-7107-1-option-b" name="quiz-option-7107" type="radio" value="passive" > <span class="option__label"> <span class="screen-reader-only">b.</span> passive </span> </label> <span class="quiz__response" id="response-7107-1"> <strong>Correct!</strong> </span> </div> </div> </div> </div> </form> </div> </section> <section id="toc_6"> <h2>The sodium/potassium pump</h2><p>Perhaps the most important pump of all is the sodium/potassium pump, usually written simply as the Na<sup>+</sup>/K<sup>+</sup> pump. This pump exists in just about every <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> <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 human body, and indeed in almost every cell membrane of every animal that has ever lived on Earth. This pump is responsible for pumping sodium out of the cell and potassium into the cell. Because it pumps two things in opposite directions, it is called an <em>antiport</em>.</p><p>Although there is already a lot of Na<sup>+</sup> outside 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> (and very little inside), the Na<sup>+</sup>/K<sup>+</sup> <mark class="term" data-term="antiport" data-term-def="A protein that simultaneously transports two different molecules, in opposite directions, across the membrane." data-term-url="/en/glossary/view/antiport/7382">antiport</mark> actively pumps Na<sup>+</sup> from inside the cell to the outside. The same is true for potassium (K<sup>+</sup>) – it actively pumps K<sup>+</sup> into the cell despite higher <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">concentrations</mark> within than without. The antiport is constantly building both gradients by increasing the concentrations of sodium outside of, and potassium inside of, the cell. The Na<sup>+</sup>/K<sup>+</sup> pump works tirelessly on every cell of the human body, constantly maintaining these two crucial gradients (Figure 6).</p>  <div class="figure"> <figure> <button class="lightbox-button" data-lightbox-src="/img/library/large_images/image_7133.jpg" data-lightbox="image"> <img src="/img/library/modules/mid204/Image/VLObject-7133-140910020910.jpg" alt="Figure 6: The sodium-potassium (Na+/K+) antiport actively pumps sodium from inside the cell to the outside while also pumping potassium into the cell." /> </button> <figcaption> <p><strong>Figure 6</strong>: The sodium-potassium (Na<sup>+</sup>/K<sup>+</sup>) antiport actively pumps sodium from inside the cell to the outside while also pumping potassium into the cell.</p> <span class="credit">image ©BruceBlaus</span> </figcaption> </figure> </div> <p>Because it is working against the natural flow of <mark class="term" data-term="diffusion" data-term-def="The movement of atoms or molecules from one part of a medium to another caused by their random thermal motion.&hellip;" data-term-url="/en/glossary/view/diffusion/2690">diffusion</mark> – to balance out the <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> on either side of the <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> – the Na<sup>+</sup>/K<sup>+</sup> pump is said to be engaged in <mark class="term" data-term="active transport" data-term-def="The opposite of passive transport, active transport involves the input of energy (usually in the form of ATP), the building of&hellip;" data-term-url="/en/glossary/view/active+transport/7380">active transport</mark>, a <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> that requires <mark class="term" data-term="energy" data-term-def="An abstract property defined as the capacity to do work. The basic forms of energy include chemical, electrical, mechanical, nuclear, and&hellip;" data-term-url="/en/glossary/view/energy/1497">energy</mark>. Like most work 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> do, the energy for this transport work comes in the form of <mark class="term" data-term="adenosine triphosphate" data-term-url="/en/glossary/view/adenosine+triphosphate" data-term-def="(ATP) Molecules that provide energy for important chemical reactions within the cell; the main energy currency of the cell.">ATP</mark>.</p><p>Why is it so important to keep the interior 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> low in Na<sup>+</sup> and high in K<sup>+</sup>? The reason is because these two gradients are used for all kinds of important purposes around the body, such as allowing nerves to send messages and muscles to contract. 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 neurons and muscles have sodium and potassium channels on them; however, these channels are not always open – they have <mark class="term" data-term="gate" data-term-def="Active ion channels can regulate the passage of ions via a gate mechanism. Gates can open (allow ions to flow&hellip;" data-term-url="/en/glossary/view/gate/7378">gates</mark> on them that are usually closed. These gates can be suddenly opened, though. For example, muscle cells have a sodium channel with a gate that can be opened by the neurotransmitter <mark class="term" data-term="acetylcholine" data-term-def="A chemical neurotransmitter. When released onto a muscle, acetylcholine will activate sodium channels to open." data-term-url="/en/glossary/view/acetylcholine/7383">acetylcholine</mark>. If a neuron suddenly releases acetylcholine onto a muscle, the gate on the sodium channel will swing open. When that happens, sodium <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> will then rush into the cell because of the ever-present sodium gradient. The sodium <mark class="term" data-term="ion" data-term-url="/en/glossary/view/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;">ions</mark> (Na<sup>+</sup>) then cause a rapid 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">reaction</mark> that leads to muscle contraction. (See Figure 7.)</p>  <div class="figure"> <figure> <button class="lightbox-button" data-lightbox-src="/img/library/large_images/image_7369.jpg" data-lightbox="image"> <img src="/img/library/modules/mid204/Image/VLObject-7369-141104011140.jpg" alt="Figure 7: A neuron releases acetylcholine onto a muscle, causing the gate on the sodium channel to swing open (inset) and sodium ions rush into the cell because of the sodium gradient. " /> </button> <figcaption> <p><strong>Figure 7</strong>: A neuron releases acetylcholine onto a muscle, causing the gate on the sodium channel to swing open (inset) and sodium ions rush into the cell because of the sodium gradient. </p> <span class="credit">image ©VL</span> </figcaption> </figure> </div> <p>During normal muscle use, the influx of sodium is temporary and is quickly reversed by the Na<sup>+</sup>/K<sup>+</sup> pump, which is always working to re-establish the gradients as quickly as possible. However, during strenuous exercise, particularly when the muscle is not accustomed to such demanding work, the Na<sup>+</sup>/K<sup>+</sup> pump and other <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">ion</mark> pumps that are important in muscle <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> function cannot keep up with the ion influx from the <mark class="term" data-term="gate" data-term-def="Active ion channels can regulate the passage of ions via a gate mechanism. Gates can open (allow ions to flow&hellip;" data-term-url="/en/glossary/view/gate/7378">gates</mark> being opened so much. This leads to a sustained and involuntary contraction of the muscle, also called a <mark class="term" data-term="cramp" data-term-def="A sustained and involuntary contraction of the muscle." data-term-url="/en/glossary/view/cramp/7384">cramp</mark>, as the sodium <mark class="term" data-term="ion" data-term-url="/en/glossary/view/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;">ions</mark> build up inside the muscle cells. Because the contraction is involuntary and very intense, cramps are painful and usually debilitating. The only way to reverse them is to stop all exercise and massage the muscle, coaxing it into a relaxed state and giving the Na<sup>+</sup>/K<sup>+</sup> pump a chance to get caught up on its job of getting sodium out of the cell, and potassium in. Athletes who are in very good shape have fewer problems with cramping because their well-trained muscles have more Na<sup>+</sup>/K<sup>+</sup> pumps, and other ion pumps, than the rest of us have.</p><p>Many neurons in your brain also respond to a sudden influx of sodium <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> by releasing neurotransmitters onto neighboring neurons. The crucial importance of these sodium channels is underscored by the fact that some of the most deadly poisonous <mark class="term" data-term="compound" data-term-def="A material formed by the chemical combination of elements in defined proportions. Compounds can be chemically decomposed into simpler substances." data-term-url="/en/glossary/view/compound/1517">compounds</mark> ever discovered are compounds that block sodium channels, paralyzing nerves and muscles. Tetrodotoxin, one such sodium channel-blocking poison found in Fugu pufferfish, is 100 times more lethal than cyanide. Ingesting even a very small dose of tetrodotoxin can completely paralyze someone by preventing both muscles and neurons from functioning (Narahashi, Moore, & Scott, 1964).</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="cc7115"> <div class="form-entry"> <div class="form-entry__field"> <span class="form-entry__field__label">_________ provides energy for active transport.</span> <div class="form-entry__option"> <div class="form-entry__option__radio" data-answer="correct"> <label> <input id="q1-7115-0-option-a" name="quiz-option-7115" type="radio" value="ATP" > <span class="option__label"> <span class="screen-reader-only">a.</span> ATP </span> </label> <span class="quiz__response" id="response-7115-0"> <strong>Correct!</strong> </span> </div> <div class="form-entry__option__radio" data-answer="incorrect"> <label> <input id="q1-7115-1-option-b" name="quiz-option-7115" type="radio" value="Potassium (K<sup>+</sup>)" > <span class="option__label"> <span class="screen-reader-only">b.</span> Potassium (K<sup>+</sup>) </span> </label> <span class="quiz__response" id="response-7115-1"> <strong>Incorrect.</strong> </span> </div> </div> </div> </div> </form> </div> </section> <section id="toc_7"> <h2>Discovery of the Na<sup>+</sup>/K<sup>+</sup> pump</h2><p>In the 1950s, scientists knew that <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> move in and out 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> and that, because of this, cells had a voltage – a difference in the <mark class="term" data-term="charge" data-term-def="A quantity of electricity." data-term-url="/en/glossary/view/charge/8258">charge</mark> inside of the cells compared to outside the cells. The voltage, also called the resting <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> potential, of nearly all cells is negative – meaning there are more negative charges inside the cell than positive <mark class="term" data-term="ion" data-term-url="/en/glossary/view/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;">ions</mark>. This internal negative charge of cells mostly comes from many of the large macromolecules of life – <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="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>, <mark class="term" data-term="lipids" data-term-def="A diverse group of organic molecules that contain long hydrocarbon chains or rings and are hydrophobic. Examples are fats, oils, waxes,&hellip;" data-term-url="/en/glossary/view/lipids/1599">lipids</mark>, and <mark class="term" data-term="sugar" data-term-def="A water-soluble crystalline carbohydrate. There are many types of sugar of varying degrees of sweetness, including fructose, which occurs naturally in&hellip;" data-term-url="/en/glossary/view/sugar/5309">sugars</mark> – which are all negatively charged. But scientists didn't understand how the cell prevented positive ions from flowing in to cancel out the negative charges, or why all animal cells maintained a low <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 sodium and a high concentration of potassium.</p><p>This changed in 1958 when Jens Skou, a Danish physician, made an accidental discovery while studying how local analgesics worked. Analgesics are substances that prevent or reduce pain; an example of a local analgesic is Novocain, which is used by dentists to numb the mouth during oral surgery. In his laboratory, Dr. Skou noticed 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> have an <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">enzyme</mark> embedded in their <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> that consumed a lot of <mark class="term" data-term="adenosine triphosphate" data-term-url="/en/glossary/view/adenosine+triphosphate" data-term-def="(ATP) Molecules that provide energy for important chemical reactions within the cell; the main energy currency of the cell.">ATP</mark>. He then noticed that when he exposed cells to some analgesics, the membrane-bound enzyme stopped consuming <mark class="term" data-term="ATP" data-term-def="Adenosine triphosphate. Molecules that provide energy for important chemical reactions within the cell." data-term-url="/en/glossary/view/ATP/6545">ATP</mark>, as if it were paralyzed. The effect would slowly wear off as the drug washed away from the cells. The crucial part of the discovery came when he noticed that the drugs didn’t only affect the mysterious ATP-consuming enzyme, but also allowed sodium to build up in the cell and potassium to leak out. No other <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 affected – just sodium and potassium. And once again, the effect wore off over time. With exactly the same timing, the ATP consumption would gradually resume and the Na+ and K+ gradients would be restored. Dr. Skou didn't immediately make the connection and went about studying other painkillers.</p><p>It was only after a conversation with another scientist, Robert Post, who was studying sodium transport in red blood <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 they both realized they could be studying the same <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">enzyme</mark>. Dr. Post went back to his lab and tried the same analgesic that Skou used, and it worked – it inhibited sodium transport in the red blood cells. Meanwhile, Skou telephoned his laboratory and instructed them to try the drug that Post had been studying, ouabain (pronounced <em>wah-bain</em>), and a few days later, his laboratory called back to say that it worked the same way (Skou, 1965).</p><p>What does inhibiting a sodium/potassium pump have to do with relieving pain? As mentioned above, the gradients of sodium and potassium are crucial for the functioning of neurons. When ouabain and other analgesics slow the Na+/K+ pump on the sensory neurons responsible for sensing pain, they temporarily disrupt the Na<sup>+</sup> and K<sup>+</sup> gradients. When this happens, the neuron is paralyzed for a while and cannot transmit its message of pain to the brain. Though the Na<sup>+</sup>/K<sup>+</sup> pump is on every <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> of the body, these drugs do not affect other cells as powerfully as they do neurons. Most cells don’t rely as much on the Na<sup>+</sup> and K<sup>+</sup> gradients to function, so these cells are not as affected by the drugs. However, there is one other type of cell that <em>is</em> affected – muscles. Both muscles and neurons are said to be <mark class="term" data-term="excitable" data-term-def="A description of cells that are very sensitive to changes in voltage and the movement of ions." data-term-url="/en/glossary/view/excitable/7386">excitable</mark>, which means that they are very sensitive to changes in voltage and movement of <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>. Drugs that inhibit the Na<sup>+</sup>/K<sup>+</sup> pump can paralyze muscles as well as neurons. </p><p>In summary, cellular <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">membranes</mark> are neither passive sacs around 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> nor solitary cell parts. Embedded in the membrane are <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 perform vital functions for the cell. Among the most important functions of these proteins is the transport of various <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> into and out of the cell. As we saw with Cystic Fibrosis, when even just one of the hundreds of transporter types in a cell membrane malfunction, serious disease can result.</p><p>At the same time, the functions of these transporters can sometimes be manipulated with pharmaceutical drugs to treat certain medical conditions. Drugs that restrain the <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">proton</mark> pumps on the stomach lining are useful in treating acid reflux, and drugs that inhibit the Na<sup>+</sup>/K<sup>+</sup> pump can act as topical pain relievers. Thus, many biomedical scientists study 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">membranes</mark> in their pursuit for treatments and cures to common medical conditions.</p></section> <footer class="module__main__footer"> <hr class="border-color-dark"> <p class="citation"> <em> Nathan H Lents, Ph.D. “Membranes II” Visionlearning Vol. BIO-3 (8), 2014. </em> </p>  <div class="title-list" id="refs" name="refs"> <p class="h6 title-list__title"> References </p> <ul class="title-list__list"> <li>Cheng, S. H., Gregory, R. J., Marshall, J., Paul, S., Souza, D. W., White, G. A., ... & Smith, A. E. (1990). Defective intracellular transport and processing of CFTR is the molecular basis of most cystic fibrosis. <em>Cell, 63</em>(4), 827-834.</li> <li>Narahashi, T., Moore, J. W., & Scott, W. R. (1964). Tetrodotoxin blockage of sodium conductance increase in lobster giant axons. <em>The Journal of General Physiology, 47</em>(5), 965-974.</li> <li>Peghini, P. L., Katz, P. O., Bracy, N. A., & Castell, D. O. (1998). Nocturnal recovery of gastric acid secretion with twice-daily dosing of proton pump inhibitors. <em>The American Journal of Gastroenterology, 93</em>(5), 763-767.</li> <li>Skou, J. C. (1965). Enzymatic basis for active transport of Na<sup>+</sup> and K<sup>+</sup> across cell membrane. <em>Physiol. Rev, 45</em>(5), 617.</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/Absorption-Distribution-and-Storage-of-Chemicals/106"> <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_106-23061209062802.jpeg" alt="Membranes and Chemical Transport"> </div> <div class="flex-grow-shrink"> <h2 class="h6 font-weight-normal"> Membranes and Chemical Transport: <em>Absorption, distribution, and storage of substances in organisms</em> </h2> </div> </article> </a> </li> <li> <a class="no-hover-focus height-100" href="/en/library/Biology/2/Cellular-Organelles-I/195"> <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_195-23061209062726.jpeg" alt="Cellular Organelles I"> </div> <div class="flex-grow-shrink"> <h2 class="h6 font-weight-normal"> Cellular Organelles I: <em>Endosymbiosis and membrane-bound organelles</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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