{"id":8543,"date":"2013-11-18T16:05:02","date_gmt":"2013-11-18T16:05:02","guid":{"rendered":"http:\/\/www.mometrix.com\/academy\/?page_id=8543"},"modified":"2026-03-25T11:04:13","modified_gmt":"2026-03-25T16:04:13","slug":"plasma-membrane","status":"publish","type":"page","link":"https:\/\/www.mometrix.com\/academy\/plasma-membrane\/","title":{"rendered":"Function of the Plasma Membrane"},"content":{"rendered":"\n\t\t\t<div id=\"mmDeferVideoEncompass_PIRpzv9_BOU\" style=\"position: relative;\">\n\t\t\t<picture>\n\t\t\t\t<source srcset=\"https:\/\/www.mometrix.com\/academy\/wp-content\/uploads\/2023\/01\/circle-play-duotone.webp\" type=\"image\/webp\">\n\t\t\t\t<source srcset=\"https:\/\/www.mometrix.com\/academy\/wp-content\/uploads\/2023\/01\/circle-play-duotone.png\" type=\"image\/jpeg\"> \n\t\t\t\t<img fetchpriority=\"high\" decoding=\"async\" loading=\"eager\" id=\"videoThumbnailImage_PIRpzv9_BOU\" data-source-videoID=\"PIRpzv9_BOU\" src=\"https:\/\/www.mometrix.com\/academy\/wp-content\/uploads\/2023\/01\/circle-play-duotone.png\" alt=\"Function of the Plasma Membrane Video\" height=\"464\" width=\"825\" class=\"size-full\" data-matomo-title = \"Function of the Plasma Membrane\">\n\t\t\t<\/picture>\n\t\t\t<\/div>\n\t\t\t<style>img#videoThumbnailImage_PIRpzv9_BOU:hover {cursor:pointer;} img#videoThumbnailImage_PIRpzv9_BOU {background-size:contain;background-image:url(\"https:\/\/www.mometrix.com\/academy\/wp-content\/uploads\/2023\/02\/421-fuction-of-the-plasma-membrane-2-1.webp\");}<\/style>\n\t\t\t<script defer>\n\t\t\t  jQuery(\"img#videoThumbnailImage_PIRpzv9_BOU\").click(function() {\n\t\t\t\tlet videoId = jQuery(this).attr(\"data-source-videoID\");\n\t\t\t\tlet helpTag = '<div id=\"mmDeferVideoYTMessage_PIRpzv9_BOU\" style=\"display: none;position: absolute;top: -24px;width: 100%;text-align: center;\"><span style=\"font-style: italic;font-size: small;border-top: 1px solid #fc0;\">Having trouble? <a href=\"https:\/\/www.youtube.com\/watch?v='+videoId+'\" target=\"_blank\">Click here to watch on YouTube.<\/a><\/span><\/div>';\n\t\t\t\tlet tag = document.createElement(\"iframe\");\n\t\t\t\ttag.id = \"yt\" + videoId;\n\t\t\t\ttag.src = \"https:\/\/www.youtube-nocookie.com\/embed\/\" + videoId + \"?autoplay=1&controls=1&wmode=opaque&rel=0&egm=0&iv_load_policy=3&hd=0&enablejsapi=1\";\n\t\t\t\ttag.frameborder = 0;\n\t\t\t\ttag.allow = \"autoplay; fullscreen\";\n\t\t\t\ttag.width = this.width;\n\t\t\t\ttag.height = this.height;\n\t\t\t\ttag.setAttribute(\"data-matomo-title\",\"Function of the Plasma Membrane\");\n\t\t\t\tjQuery(\"div#mmDeferVideoEncompass_PIRpzv9_BOU\").html(tag);\n\t\t\t\tjQuery(\"div#mmDeferVideoEncompass_PIRpzv9_BOU\").prepend(helpTag);\n\t\t\t\tsetTimeout(function(){jQuery(\"div#mmDeferVideoYTMessage_PIRpzv9_BOU\").css(\"display\", \"block\");}, 2000);\n\t\t\t  });\n\t\t\t  \n\t\t\t<\/script>\n\t\t\n<p><script>\nfunction MJa_Function() {\n  var x = document.getElementById(\"MJa\");\n  if (x.style.display === \"none\") {\n    x.style.display = \"block\";\n  } else {\n    x.style.display = \"none\";\n  }\n}\n<\/script><\/p>\n<div class=\"moc-toc hide-on-desktop hide-on-tablet\">\n<div><button onclick=\"MJa_Function()\"><img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/www.mometrix.com\/academy\/wp-content\/uploads\/2024\/12\/toc2.svg\" width=\"16\" height=\"16\" alt=\"show or hide table of contents\"><\/button><\/p>\n<p>On this page<\/p>\n<\/div>\n<nav id=\"MJa\" style=\"display:none;\">\n<ul>\n<li class=\"toc-h2\"><a href=\"#Phospholipid_Bilayer\" class=\"smooth-scroll\">Phospholipid Bilayer<\/a><\/li>\n<li class=\"toc-h2\"><a href=\"#Membrane_Fluidity\" class=\"smooth-scroll\">Membrane Fluidity<\/a><\/li>\n<li class=\"toc-h2\"><a href=\"#Membrane_Proteins\" class=\"smooth-scroll\">Membrane Proteins<\/a><\/li>\n<li class=\"toc-h2\"><a href=\"#Passive_and_Active_Transport_and_Facilitated_Diffusion\" class=\"smooth-scroll\">Passive and Active Transport and Facilitated Diffusion<\/a><\/li>\n<li class=\"toc-h2\"><a href=\"#Cytoskeleton_and_Cell_Walls\" class=\"smooth-scroll\">Cytoskeleton and Cell Walls<\/a><\/li>\n<li class=\"toc-h2\"><a href=\"#Cell_Walls\" class=\"smooth-scroll\">Cell Walls<\/a><\/li>\n<li class=\"toc-h2\"><a href=\"#Frequently_Asked_Questions\" class=\"smooth-scroll\">Frequently Asked Questions<\/a><\/li>\n<\/ul>\n<\/nav>\n<\/div>\n<div class=\"accordion\"><input id=\"transcript\" type=\"checkbox\" class=\"spoiler_button\" \/><label for=\"transcript\">Transcript<\/label><input id=\"FAQs\" type=\"checkbox\" class=\"spoiler_button\" \/><label for=\"FAQs\">FAQs<\/label>\n<div class=\"spoiler\" id=\"transcript-spoiler\">\n<p>Hey guys! Welcome to this Mometrix video over the functions of the plasma membrane.<\/p>\n<p>The plasma membrane is highly important to the life of a cell! It\u2019s what separates the <strong>intracellular environment<\/strong> (the cytoplasm) of cells from the <strong>extracellular space<\/strong> into distinct units known as cells. The plasma membrane also regulates the movement of materials in and out of the cell and provides structure to the <a class=\"ylist\" href=\"https:\/\/www.mometrix.com\/academy\/introduction-to-cellular-biology\/\">cells<\/a>. In this video, we\u2019ll look at what makes the plasma membrane and what it does. <\/p>\n<h2><span id=\"Phospholipid_Bilayer\" class=\"m-toc-anchor\"><\/span>Phospholipid Bilayer<\/h2>\n<h3><span id=\"Fluid_Mosaic_Model\" class=\"m-toc-anchor\"><\/span>Fluid Mosaic Model<\/h3>\n<p>\n<img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/www.mometrix.com\/academy\/wp-content\/uploads\/2021\/08\/1200px-Cell_membrane_detailed_diagram_en.svg_.png\" alt=\"\" width=\"1200\" height=\"494\" class=\"aligncenter size-full wp-image-87586\" srcset=\"https:\/\/www.mometrix.com\/academy\/wp-content\/uploads\/2021\/08\/1200px-Cell_membrane_detailed_diagram_en.svg_.png 1200w, https:\/\/www.mometrix.com\/academy\/wp-content\/uploads\/2021\/08\/1200px-Cell_membrane_detailed_diagram_en.svg_-300x124.png 300w, https:\/\/www.mometrix.com\/academy\/wp-content\/uploads\/2021\/08\/1200px-Cell_membrane_detailed_diagram_en.svg_-1024x422.png 1024w, https:\/\/www.mometrix.com\/academy\/wp-content\/uploads\/2021\/08\/1200px-Cell_membrane_detailed_diagram_en.svg_-768x316.png 768w\" sizes=\"auto, (max-width: 1200px) 100vw, 1200px\" \/><\/p>\n<p>There\u2019s a lot going on in the cell\u2019s membrane! In 1972, S. J. Singer and G. L. Nicolson came up with a model to imagine the cell membrane, known as the fluid mosaic model. This describes the membrane as a fluid phospholipid bilayer containing a mix or mosaic of <a href=\"https:\/\/www.mometrix.com\/academy\/proteins\/\"><strong>proteins<\/strong><\/a>, cholesterol, and carbohydrates. <\/p>\n<p>To break that down, phospholipids are a type of lipid with <strong>hydrophobic<\/strong> (or \u201cwater-fearing\u201d) fatty acid tails and a <strong>hydrophilic<\/strong> (or \u201cwater-loving\u201d) phosphate group as their head. This combination of a hydrophilic and hydrophobic region makes them known as <strong>amphipathic<\/strong>. With these arranged side-by-side in two layers, with the tails facing each other and the heads opposite, this makes it a bilayer. The combination of hydrophilic and hydrophobic regions of the bilayer keeps the cell from unwanted leaking of water and other substances. The separate polar and non-polar layers of the membrane keep all but the smallest non-polar molecules such as O2 and CO2 from diffusing across the membrane. <\/p>\n<h2><span id=\"Membrane_Fluidity\" class=\"m-toc-anchor\"><\/span>Membrane Fluidity<\/h2>\n<p>\nAn important aspect of the phospholipid bilayer is how flexible it is, or its fluidity, which impacts its ability to function as a barrier and as transportation. For this reason, it cannot be too rigid or too fluid and has a varied composition. The fluidity of the bilayer is affected by temperature and the composition of the membrane. With more heat, the membrane becomes more fluid due to the excitement of molecules. Unsaturated fatty acids have double bonds between carbons, which forms a bend or kink, reducing the packing capability of these molecules.<\/p>\n<p>If the membrane was composed entirely of saturated fatty acids, the phospholipid tail would be packed closely side-by-side, and it would be too rigid. However, by incorporating more unsaturated fatty acids, the membrane becomes more fluid. The fluidity of the membrane is also affected by cholesterol and proteins, which are also found in the membrane.<\/p>\n<p>Cholesterol is a type of lipid that is a modified steroid, which contains four carbon rings and a hydrocarbon chain. It reduces membrane fluidity, resists changes in fluidity due to temperature, and also helps prevent materials from leaking through the membrane. Proteins are large, highly functional macromolecules that are found along the plane of the membrane.<\/p>\n<h2><span id=\"Membrane_Proteins\" class=\"m-toc-anchor\"><\/span>Membrane Proteins<\/h2>\n<p>\nA major feature of the plasma membrane is the presence of its membrane proteins. Membrane proteins can either be found on one or both sides of the membrane, and are referred to as peripheral proteins, integral membrane proteins, or transmembrane proteins.<\/p>\n<p>Peripheral proteins are temporarily bound to the membrane by hydrogen bonding or other weak non-covalent interactions and often serve as enzymes or receptor proteins. Integral membrane proteins are those which have hydrophilic and hydrophobic regions that allow them to line up with the hydrophobic region of the membrane and the intracellular or extracellular space.<\/p>\n<p>Transmembrane proteins are integral proteins that have regions exposed in both the cell\u2019s cytoplasm and the extracellular fluid. These integral proteins can drift in the plane of the membrane, but some are stationary.<\/p>\n<h2><span id=\"Passive_and_Active_Transport_and_Facilitated_Diffusion\" class=\"m-toc-anchor\"><\/span>Passive and Active Transport and Facilitated Diffusion<\/h2>\n<p>\nSo we know that most material can\u2019t just easily move through the phospholipid bilayer. Instead, movement of substances in and out of the cell is accomplished through <strong>transport proteins<\/strong> found in the membrane. There are two main types of transport proteins: channels and carriers. <\/p>\n<p><strong>Channels<\/strong> are either open or closed to both sides of the cell and allow for the diffusion of hundreds of specific or similar molecules at a time. This type of movement is referred to as passive transport, where substances diffuse down their chemical gradient to the area of a lower concentration. <\/p>\n<p><strong>Carrier<\/strong> proteins are only open on one side at a time and move specific molecules across the membrane that can react with the carrier\u2019s active site, which is where substrates bind to a protein to cause a conformational change, or change in its form and thus function. These carrier proteins are used in active transport, which unlike passive transport, moves substances against their gradient, often to create a high concentration in the cell. Active transport costs energy in the form of ATP to create a conformational change. Another type of transport by carrier proteins is facilitated diffusion, which is a form of passive transport. Polar molecules and large ions can\u2019t move through channel proteins. They move through specific transport proteins to cross the plasma membrane. <\/p>\n<h2><span id=\"Cytoskeleton_and_Cell_Walls\" class=\"m-toc-anchor\"><\/span>Cytoskeleton and Cell Walls<\/h2>\n<p>\nIn addition to allowing transport of specific material across the membrane, proteins in the membrane also function as an anchor for the cytoskeleton, a scaffold made of microfilaments, intermediate filaments, and microtubules. It provides stability to the cell and allows for intracellular transport, or movement of objects inside the cell, such as organelles or vacuoles.<\/p>\n<h2><span id=\"Cell_Walls\" class=\"m-toc-anchor\"><\/span>Cell Walls<\/h2>\n<p>\nSome cells also feature cell walls. These are thicker structures mostly found surrounding the outside of the plasma membrane in bacteria, plants, and fungi. The structure of the cell wall depends on the type of organism it\u2019s in. In plants, cell walls have three layers: the primary cell wall, secondary cell wall, and middle lamella.<\/p>\n<p>The <strong>primary<\/strong> cell walls are made mostly from three polysaccharides: cellulose which forms long, linear chains; hemicellulose, which is a smaller, branching polysaccharide; and pectin.<\/p>\n<p>In the <strong>secondary<\/strong> cell wall is primarily cellulose, xylan, and lignin, while the <strong>middle lamella<\/strong> is mostly pectin. In bacteria, it is formed primarily of peptidoglycan which forms linear polysaccharide chains cross-linked by peptides. In fungi, the cell wall is formed mostly from chitin, which is a glucose derivative, and polysaccharides, though true fungi do not have cellulose in their cell walls.<\/p>\n<p>I hope that this overview was helpful, see you guys next time!<\/p>\n<\/div>\n<div class=\"spoiler\" id=\"FAQs-spoiler\">\n<h2 style=\"text-align:center\"><span id=\"Frequently_Asked_Questions\" class=\"m-toc-anchor\"><\/span>Frequently Asked Questions<\/h2>\n<div class=\"faq-list\">\n<div class=\"qa_wrap\">\n<div class=\"q_item text_bold\">\n<h4 class=\"letter\">Q<\/h4>\n<p style=\"line-height: unset;\">What is the plasma membrane?<\/p>\n<\/p><\/div>\n<div class=\"a_item\">\n<h4 class=\"letter text_bold\">A<\/h4>\n<p>The plasma membrane, or cell membrane, is a semipermeable membrane within all cells that helps separate the internal parts of the cell from the external environment.<\/p>\n<\/p><\/div>\n<\/p><\/div>\n<div class=\"qa_wrap\">\n<div class=\"q_item text_bold\">\n<h4 class=\"letter\">Q<\/h4>\n<p style=\"line-height: unset;\">What is the function of the plasma membrane?<\/p>\n<\/p><\/div>\n<div class=\"a_item\">\n<h4 class=\"letter text_bold\">A<\/h4>\n<p>The plasma membrane acts as a barrier by isolating the cell from its external environment while still enabling the cell to communicate with that outside environment. It also determines what molecules, such as ions, nutrients, and wastes, are allowed to enter and exit the cell. <\/p>\n<\/p><\/div>\n<\/p><\/div>\n<div class=\"qa_wrap\">\n<div class=\"q_item text_bold\">\n<h4 class=\"letter\">Q<\/h4>\n<p style=\"line-height: unset;\">What is the plasma membrane made of?<\/p>\n<\/p><\/div>\n<div class=\"a_item\">\n<h4 class=\"letter text_bold\">A<\/h4>\n<p>The plasma membrane is a thin semipermeable membrane of lipids and proteins. It consists of a phospholipid bilayer, or double layer, with the hydrophilic (\u201cwater-loving\u201d) ends of the outer layer facing the external environment, the inner layer facing the inside of the cell, and the hydrophobic (\u201cwater-fearing\u201d) ends facing each other. Cholesterol in the cell membrane adds stiffness and flexibility. Glycolipids help the cell to recognize other cells of the organisms. The proteins in the cell membrane help give the cells shape. Special proteins help the cell communicate with its external environment, while other proteins transport molecules across the cell membrane.<\/p>\n<p><img loading=\"lazy\" decoding=\"async\" class=\"alignnone  wp-image-64599\" src=\"https:\/\/www.mometrix.com\/academy\/wp-content\/uploads\/2020\/12\/plasma-membrane.png\" alt=\"\" width=\"939\" height=\"400\" srcset=\"https:\/\/www.mometrix.com\/academy\/wp-content\/uploads\/2020\/12\/plasma-membrane.png 3930w, https:\/\/www.mometrix.com\/academy\/wp-content\/uploads\/2020\/12\/plasma-membrane-300x128.png 300w, https:\/\/www.mometrix.com\/academy\/wp-content\/uploads\/2020\/12\/plasma-membrane-1024x437.png 1024w, https:\/\/www.mometrix.com\/academy\/wp-content\/uploads\/2020\/12\/plasma-membrane-768x328.png 768w, https:\/\/www.mometrix.com\/academy\/wp-content\/uploads\/2020\/12\/plasma-membrane-1536x655.png 1536w, https:\/\/www.mometrix.com\/academy\/wp-content\/uploads\/2020\/12\/plasma-membrane-2048x874.png 2048w\" sizes=\"auto, (max-width: 939px) 100vw, 939px\" \/><\/p>\n<\/p><\/div>\n<\/p><\/div>\n<div class=\"qa_wrap\">\n<div class=\"q_item text_bold\">\n<h4 class=\"letter\">Q<\/h4>\n<p style=\"line-height: unset;\">Do prokaryotes have a plasma membrane?<\/p>\n<\/p><\/div>\n<div class=\"a_item\">\n<h4 class=\"letter text_bold\">A<\/h4>\n<p>Both prokaryotic and eukaryotic cells have a plasma membrane.<\/p>\n<\/p><\/div>\n<\/p><\/div>\n<div class=\"qa_wrap\">\n<div class=\"q_item text_bold\">\n<h4 class=\"letter\">Q<\/h4>\n<p style=\"line-height: unset;\">Do plant cells have a plasma membrane?<\/p>\n<\/p><\/div>\n<div class=\"a_item\">\n<h4 class=\"letter text_bold\">A<\/h4>\n<p>While plant cells are stiffer due to their cell wall, plant cells still contain a plasma membrane. <\/p>\n<\/p><\/div>\n<\/p><\/div>\n<\/div>\n<\/div>\n<\/div>\n\n<div class=\"home-buttons\">\n<p><a href=\"https:\/\/www.mometrix.com\/academy\/biology\/\">Return to Biology Videos<\/a><\/p>\n<\/div>\n","protected":false},"excerpt":{"rendered":"<p>Return to Biology Videos<\/p>\n","protected":false},"author":1,"featured_media":95299,"parent":0,"menu_order":0,"comment_status":"closed","ping_status":"open","template":"","meta":{"footnotes":""},"class_list":{"0":"post-8543","1":"page","2":"type-page","3":"status-publish","4":"has-post-thumbnail","6":"page_category-cell-biology-videos","7":"page_type-video","8":"subject_matter-science"},"aioseo_notices":[],"_links":{"self":[{"href":"https:\/\/www.mometrix.com\/academy\/wp-json\/wp\/v2\/pages\/8543","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.mometrix.com\/academy\/wp-json\/wp\/v2\/pages"}],"about":[{"href":"https:\/\/www.mometrix.com\/academy\/wp-json\/wp\/v2\/types\/page"}],"author":[{"embeddable":true,"href":"https:\/\/www.mometrix.com\/academy\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/www.mometrix.com\/academy\/wp-json\/wp\/v2\/comments?post=8543"}],"version-history":[{"count":5,"href":"https:\/\/www.mometrix.com\/academy\/wp-json\/wp\/v2\/pages\/8543\/revisions"}],"predecessor-version":[{"id":279115,"href":"https:\/\/www.mometrix.com\/academy\/wp-json\/wp\/v2\/pages\/8543\/revisions\/279115"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/www.mometrix.com\/academy\/wp-json\/wp\/v2\/media\/95299"}],"wp:attachment":[{"href":"https:\/\/www.mometrix.com\/academy\/wp-json\/wp\/v2\/media?parent=8543"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}