{"id":571,"date":"2018-05-03T17:46:43","date_gmt":"2018-05-03T17:46:43","guid":{"rendered":"https:\/\/courses.lumenlearning.com\/suny-osbiology2e\/chapter\/the-endomembrane-system-and-proteins\/"},"modified":"2018-06-27T14:40:51","modified_gmt":"2018-06-27T14:40:51","slug":"the-endomembrane-system-and-proteins","status":"publish","type":"chapter","link":"https:\/\/courses.lumenlearning.com\/suny-osbiology2e\/chapter\/the-endomembrane-system-and-proteins\/","title":{"raw":"The Endomembrane System and Proteins","rendered":"The Endomembrane System and Proteins"},"content":{"raw":"<div class=\"textbox learning-objectives\">\r\n<h3>Learning Objectives<\/h3>\r\nBy the end of this section, you will be able to do the following:\r\n<ul>\r\n \t<li>List the components of the endomembrane system<\/li>\r\n \t<li>Recognize the relationship between the endomembrane system and its functions<\/li>\r\n<\/ul>\r\n<\/div>\r\n<p id=\"fs-id1443008\">The endomembrane system (endo = \u201cwithin\u201d) is a group of membranes and organelles (<a class=\"autogenerated-content\" href=\"#fig-ch04-04-01\">(Figure)<\/a>) in eukaryotic cells that works together to modify, package, and transport lipids and proteins. It includes the nuclear envelope, lysosomes, and vesicles, which we have already mentioned, and the endoplasmic reticulum and Golgi apparatus, which we will cover shortly. Although not technically <em>within<\/em> the cell, the plasma membrane is included in the endomembrane system because, as you will see, it interacts with the other endomembranous organelles. The endomembrane system does not include either mitochondria or chloroplast membranes.<\/p>\r\n\r\n<div id=\"fs-id1721886\">\r\n<div class=\"textbox examples\">\r\n<h3>Art Connection<\/h3>\r\n[caption id=\"\" align=\"aligncenter\" width=\"350\"]<img src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/3206\/2018\/05\/03174630\/Figure_04_04_01.png\" alt=\"The left part of this figure shows the rough ER with an integral membrane protein embedded in it. The part of the protein facing the inside of the ER has a carbohydrate attached to it. The protein is shown leaving the ER in a vesicle that fuses with the cis side of the Golgi apparatus. The Golgi apparatus consists of several layers of membranes, called cisternae. As the protein passes through the cisternae, it is further modified by the addition of more carbohydrates. Eventually, it leaves the trans face of the Golgi in a vesicle. The vesicle fuses with the cell membrane so that the carbohydrate that was on the inside of the vesicle now faces the outside of the membrane. At the same time, the contents of the vesicle are ejected from the cell.\" width=\"350\" height=\"835\" \/> <strong>Figure 1. <\/strong>Membrane and secretory proteins are synthesized in the rough endoplasmic reticulum (RER). The RER also sometimes modifies proteins. In this illustration, an attachment of a (purple) carbohydrate modifies a (green) integral membrane protein in the ER. Vesicles with the integral protein bud from the ER and fuse with the Golgi apparatus' cis face. As the protein passes along the Golgi\u2019s cisternae, the addition of more carbohydrates further modifies it. After its synthesis is complete, it exits as an integral membrane protein of the vesicle that buds from the Golgi\u2019s <strong>trans<\/strong> face. When the vesicle fuses with the cell membrane, the protein becomes an integral portion of that cell membrane. (credit: modification of work by Magnus Manske)[\/caption]\r\n\r\nIf a peripheral membrane protein were synthesized in the lumen (inside) of the ER, would it end up on the inside or outside of the plasma membrane?\r\n\r\n<\/div>\r\n<\/div>\r\n<div id=\"fs-id2028479\" class=\"bc-section section\">\r\n<h3>The Endoplasmic Reticulum<\/h3>\r\n<p id=\"fs-id1775048\">The endoplasmic reticulum (ER) (<a class=\"autogenerated-content\" href=\"#fig-ch04-04-01\">(Figure)<\/a>) is a series of interconnected membranous sacs and tubules that collectively modifies proteins and synthesizes lipids. However, these two functions take place in separate areas of the ER: the rough ER and the smooth ER, respectively.<\/p>\r\nWe call the ER tubules' hollow portion the lumen or cisternal space. The ER's membrane, which is a phospholipid bilayer embedded with proteins, is continuous with the nuclear envelope.\r\n<div id=\"fs-id1234002\" class=\"bc-section section\">\r\n<h4>Rough ER<\/h4>\r\n<p id=\"fs-id1207356\">Scientists have named the rough endoplasmic reticulum (RER) as such because the ribosomes attached to its cytoplasmic surface give it a studded appearance when viewing it through an electron microscope (<a class=\"autogenerated-content\" href=\"#fig-ch04-04-02\">(Figure)<\/a>).<\/p>\r\n\r\n<div id=\"fig-ch04-04-02\" class=\"wp-caption aligncenter\">\r\n\r\n[caption id=\"\" align=\"aligncenter\" width=\"350\"]<img src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/3206\/2018\/05\/03174634\/Figure_04_04_02_new.jpg\" alt=\"In this transmission electron micrograph, the nucleus is the most prominent feature. The nucleolus is a circular, dark region inside the nucleus. A nuclear pore can be seen in the nuclear envelope that surrounds the nucleus. The rough endoplasmic reticulum surrounds the nucleus, appearing as many layers of membranes. A mitochondrion sits between the layers of the ER membrane.\" width=\"350\" height=\"257\" \/> <strong>Figure 2. <\/strong>This transmission electron micrograph shows the rough endoplasmic reticulum and other organelles in a pancreatic cell. (credit: modification of work by Louisa Howard)[\/caption]\r\n\r\n<\/div>\r\nRibosomes transfer their newly synthesized proteins into the RER's lumen where they undergo structural modifications, such as folding or acquiring side chains. These modified proteins incorporate into cellular membranes\u2014the ER or the ER's or other organelles' membranes. The proteins can also secrete from the cell (such as protein hormones, enzymes). The RER also makes phospholipids for cellular membranes.\r\n<p id=\"fs-id1752751\">If the phospholipids or modified proteins are not destined to stay in the RER, they will reach their destinations via transport vesicles that bud from the RER\u2019s membrane (<a class=\"autogenerated-content\" href=\"#fig-ch04-04-01\">(Figure)<\/a>).<\/p>\r\n<p id=\"fs-id2028331\">Since the RER is engaged in modifying proteins (such as enzymes, for example) that secrete from the cell, you would be correct in assuming that the RER is abundant in cells that secrete proteins. This is the case with liver cells, for example.<\/p>\r\n\r\n<\/div>\r\n<div id=\"fs-id1603907\" class=\"bc-section section\">\r\n<h4>Smooth ER<\/h4>\r\n<p id=\"fs-id1459714\">The smooth endoplasmic reticulum (SER) is continuous with the RER but has few or no ribosomes on its cytoplasmic surface (<a class=\"autogenerated-content\" href=\"#fig-ch04-04-01\">(Figure)<\/a>). SER functions include synthesis of carbohydrates, lipids, and steroid hormones; detoxification of medications and poisons; and storing calcium ions.<\/p>\r\n<p id=\"fs-id1303729\">In muscle cells, a specialized SER, the sarcoplasmic reticulum, is responsible for storing calcium ions that are needed to trigger the muscle cells' coordinated contractions.<\/p>\r\n\r\n<div class=\"interactive textbox tryit\">\r\n<h3>Link to Learning<\/h3>\r\n<p id=\"fs-id2215743\">You can watch an excellent animation of the endomembrane system <a href=\"http:\/\/openstax.org\/l\/insane_in_the_endomembrane\" target=\"_window\">here<\/a>. At the end of the animation, there is a short self-assessment.<\/p>\r\n\r\n<\/div>\r\n<div id=\"fs-id1912861\" class=\"career textbox examples\">\r\n<h3>Career Connection<\/h3>\r\n<strong>Cardiologist<\/strong>\r\n\r\nHeart disease is the leading cause of death in the United States. This is primarily due to our sedentary lifestyle and our high trans-fat diets.\r\n\r\nHeart failure is just one of many disabling heart conditions. Heart failure does not mean that the heart has stopped working. Rather, it means that the heart can\u2019t pump with sufficient force to transport oxygenated blood to all the vital organs. Left untreated, heart failure can lead to kidney failure and other organ failure.\r\n\r\nCardiac muscle tissue comprises the heart's wall. Heart failure occurs when cardiac muscle cells' endoplasmic reticula do not function properly. As a result, an insufficient number of calcium ions are available to trigger a sufficient contractile force.\r\n<p id=\"fs-id1430174\">Cardiologists (cardi- = \u201cheart\u201d; -ologist = \u201cone who studies\u201d) are doctors who specialize in treating heart diseases, including heart failure. Cardiologists can diagnose heart failure via a physical examination, results from an electrocardiogram (ECG, a test that measures the heart's electrical activity), a chest X-ray to see whether the heart is enlarged, and other tests. If the cardiologist diagnoses heart failure, he or she will typically prescribe appropriate medications and recommend a reduced table salt intake and a supervised exercise program.<\/p>\r\n\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n<div id=\"fs-id1664568\" class=\"bc-section section\">\r\n<h3>The Golgi Apparatus<\/h3>\r\n<p id=\"fs-id1340070\">We have already mentioned that vesicles can bud from the ER and transport their contents elsewhere, but where do the vesicles go? Before reaching their final destination, the lipids or proteins within the transport vesicles still need sorting, packaging, and tagging so that they end up in the right place. Sorting, tagging, packaging, and distributing lipids and proteins takes place in the Golgi apparatus (also called the Golgi body), a series of flattened membranes (<a class=\"autogenerated-content\" href=\"#fig-ch04-04-03\">(Figure)<\/a>).<\/p>\r\n\r\n<div id=\"fig-ch04-04-03\" class=\"wp-caption aligncenter\">\r\n\r\n[caption id=\"\" align=\"aligncenter\" width=\"350\"]<img src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/3206\/2018\/05\/03174636\/Figure_04_04_03.jpg\" alt=\"In this transmission electron micrograph, the Golgi apparatus appears as a stack of membranes surrounded by unnamed organelles.\" width=\"350\" height=\"275\" \/> <strong>Figure 3. <\/strong>The Golgi apparatus in this white blood cell is visible as a stack of semicircular, flattened rings in the lower portion of the image. You can see several vesicles near the Golgi apparatus. (credit: modification of work by Louisa Howard)[\/caption]\r\n\r\n<\/div>\r\n<p id=\"fs-id1726293\">We call the Golgi apparatus' the <em>cis<\/em> face. The opposite side is the <em>trans<\/em> face. The transport vesicles that formed from the ER travel to the <em>cis<\/em> face, fuse with it, and empty their contents into the Golgi apparatus' lumen. As the proteins and lipids travel through the Golgi, they undergo further modifications that allow them to be sorted. The most frequent modification is adding short sugar molecule chains. These newly modified proteins and lipids then tag with phosphate groups or other small molecules in order to travel to their proper destinations.<\/p>\r\n<p id=\"fs-id1716512\">Finally, the modified and tagged proteins are packaged into secretory vesicles that bud from the Golgi's <em>trans<\/em> face. While some of these vesicles deposit their contents into other cell parts where they will be used, other secretory vesicles fuse with the plasma membrane and release their contents outside the cell.<\/p>\r\nIn another example of form following function, cells that engage in a great deal of secretory activity (such as salivary gland cells that secrete digestive enzymes or immune system cells that secrete antibodies) have an abundance of Golgi.\r\n<p id=\"fs-id1006507\">In plant cells, the Golgi apparatus has the additional role of synthesizing polysaccharides, some of which are incorporated into the cell wall and some of which other cell parts use.<\/p>\r\n\r\n<div id=\"fs-id1618891\" class=\"career textbox examples\">\r\n<h3>Career Connection<\/h3>\r\n<p id=\"fs-id2358461\"><strong>Geneticist<\/strong><\/p>\r\nMany diseases arise from genetic mutations that prevent synthesizing critical proteins. One such disease is Lowe disease (or oculocerebrorenal syndrome, because it affects the eyes, brain, and kidneys). In Lowe disease, there is a deficiency in an enzyme localized to the Golgi apparatus. Children with Lowe disease are born with cataracts, typically develop kidney disease after the first year of life, and may have impaired mental abilities.\r\n<p id=\"fs-id1993778\">A mutation on the X chromosome causes Lowe disease. The X chromosome is one of the two human sex chromosomes, as these chromosomes determine a person's sex. Females possess two X chromosomes while males possess one X and one Y chromosome. In females, the genes on only one of the two X chromosomes are expressed. Females who carry the Lowe disease gene on one of their X chromosomes are carriers and do not show symptoms of the disease. However, males only have one X chromosome and the genes on this chromosome are always expressed. Therefore, males will always have Lowe disease if their X chromosome carries the Lowe disease gene. Geneticists have identified the mutated gene's location, as well as many other mutation locations that cause genetic diseases. Through prenatal testing, a woman can find out if the fetus she is carrying may be afflicted with one of several genetic diseases.<\/p>\r\n<p id=\"fs-id1126762\">Geneticists analyze prenatal genetic test results and may counsel pregnant women on available options. They may also conduct genetic research that leads to new drugs or foods, or perform DNA analyses for forensic investigations.<\/p>\r\n\r\n<\/div>\r\n<\/div>\r\n<div id=\"fs-id1482669\" class=\"bc-section section\">\r\n<h3>Lysosomes<\/h3>\r\n<p id=\"fs-id1986769\">In addition to their role as the digestive component and organelle-recycling facility of animal cells, lysosomes are part of the endomembrane system. Lysosomes also use their hydrolytic enzymes to destroy pathogens (disease-causing organisms) that might enter the cell. A good example of this occurs in macrophages, a group of white blood cells which are part of your body\u2019s immune system. In a process that scientists call phagocytosis or endocytosis, a section of the macrophage's plasma membrane invaginates (folds in) and engulfs a pathogen. The invaginated section, with the pathogen inside, then pinches itself off from the plasma membrane and becomes a vesicle. The vesicle fuses with a lysosome. The lysosome\u2019s hydrolytic enzymes then destroy the pathogen (<a class=\"autogenerated-content\" href=\"#fig-ch04-04-04\">(Figure)<\/a>).<\/p>\r\n\r\n<div id=\"fig-ch04-04-04\" class=\"wp-caption aligncenter\">\r\n\r\n[caption id=\"\" align=\"aligncenter\" width=\"450\"]<img src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/3206\/2018\/05\/03174641\/Figure_04_04_04.png\" alt=\"In this illustration, a eukaryotic cell is shown consuming a bacterium. As the bacterium is consumed, it is encapsulated in a vesicle. The vesicle fuses with a lysosome, and proteins inside the lysosome digest the bacterium.\" width=\"450\" height=\"1097\" \/> <strong>Figure 4. <\/strong>A macrophage has engulfed (phagocytized) a potentially pathogenic bacterium and then fuses with lysosomes within the cell to destroy the pathogen. Other organelles are present in the cell but for simplicity we do not show them.[\/caption]\r\n\r\n<\/div>\r\n<\/div>\r\n<div id=\"fs-id1687072\" class=\"summary textbox key-takeaways\">\r\n<h3>Section Summary<\/h3>\r\nThe endomembrane system includes the nuclear envelope, lysosomes, vesicles, the ER, and Golgi apparatus, as well as the plasma membrane. These cellular components work together to modify, package, tag, and transport proteins and lipids that form the membranes.\r\n\r\nThe RER modifies proteins and synthesizes phospholipids in cell membranes. The SER synthesizes carbohydrates, lipids, and steroid hormones; engages in the detoxification of medications and poisons; and stores calcium ions. Sorting, tagging, packaging, and distributing lipids and proteins take place in the Golgi apparatus. Budding RER and Golgi membranes create lysosomes. Lysosomes digest macromolecules, recycle worn-out organelles, and destroy pathogens.\r\n\r\n<\/div>\r\n<div id=\"fs-id2075509\" class=\"art-exercise\">\r\n<h3>Art Connections<\/h3>\r\n<div id=\"fs-id1570796\">\r\n<div id=\"fs-id1879455\">\r\n<p id=\"fs-id1416538\"><a class=\"autogenerated-content\" href=\"#fig-ch04-04-01\">(Figure)<\/a> If a peripheral membrane protein were synthesized in the lumen (inside) of the ER, would it end up on the inside or outside of the plasma membrane?<\/p>\r\n\r\n<\/div>\r\n<div>\r\n<p id=\"fs-id1722059\">\r\n[reveal-answer q=\"305623\"]Show Solution[\/reveal-answer]\r\n[hidden-answer a=\"305623\"]<\/p>\r\n<a href=\"#fig-ch04-04-01\">(Figure)<\/a> It would end up on the outside. After the vesicle passes through the Golgi apparatus and fuses with the plasma membrane, it turns inside out.[\/hidden-answer]\r\n\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n<div id=\"fs-id1904682\" class=\"multiple-choice textbox exercises\">\r\n<h3>Review Questions<\/h3>\r\n<div id=\"fs-id1486983\">\r\n<div>\r\n<p id=\"fs-id2029669\">Which of the following is not a component of the endomembrane system?<\/p>\r\n\r\n<ol id=\"fs-id2215260\" type=\"a\">\r\n \t<li>mitochondrion<\/li>\r\n \t<li>Golgi apparatus<\/li>\r\n \t<li>endoplasmic reticulum<\/li>\r\n \t<li>lysosome<\/li>\r\n<\/ol>\r\n<\/div>\r\n[reveal-answer q=\"fs-id1970249\"]Show Solution[\/reveal-answer]\r\n[hidden-answer a=\"fs-id1970249\"]\r\n<div id=\"fs-id1970249\">\r\n<p id=\"fs-id2027385\">A<\/p>\r\n\r\n<\/div>\r\n[\/hidden-answer]\r\n\r\n<\/div>\r\n<div>\r\n<div id=\"fs-id1987167\">\r\n<p id=\"fs-id1806761\">The process by which a cell engulfs a foreign particle is known as:<\/p>\r\n\r\n<ol id=\"fs-id1316992\" type=\"a\">\r\n \t<li>endosymbiosis<\/li>\r\n \t<li>phagocytosis<\/li>\r\n \t<li>hydrolysis<\/li>\r\n \t<li>membrane synthesis<\/li>\r\n<\/ol>\r\n<\/div>\r\n[reveal-answer q=\"fs-id2025979\"]Show Solution[\/reveal-answer]\r\n[hidden-answer a=\"fs-id2025979\"]\r\n<div id=\"fs-id2025979\">\r\n<p id=\"fs-id1774676\">B<\/p>\r\n\r\n<\/div>\r\n[\/hidden-answer]\r\n\r\n<\/div>\r\n<div>\r\n<div id=\"fs-id1734531\">\r\n\r\nWhich of the following is most likely to have the greatest concentration of smooth endoplasmic reticulum?\r\n<ol id=\"fs-id1735841\" type=\"a\">\r\n \t<li>a cell that secretes enzymes<\/li>\r\n \t<li>a cell that destroys pathogens<\/li>\r\n \t<li>a cell that makes steroid hormones<\/li>\r\n \t<li>a cell that engages in photosynthesis<\/li>\r\n<\/ol>\r\n<\/div>\r\n[reveal-answer q=\"fs-id1386336\"]Show Solution[\/reveal-answer]\r\n[hidden-answer a=\"fs-id1386336\"]\r\n<div id=\"fs-id1386336\">\r\n<p id=\"fs-id2367542\">C<\/p>\r\n\r\n<\/div>\r\n[\/hidden-answer]\r\n\r\n<\/div>\r\n<div id=\"fs-id1703517\">\r\n<div>\r\n\r\nWhich of the following sequences correctly lists in order the steps involved in the incorporation of a proteinaceous molecule within a cell?\r\n<ol id=\"fs-id1644310\" type=\"a\">\r\n \t<li>protein synthesis of the protein on the ribosome; modification in the Golgi apparatus; packaging in the endoplasmic reticulum; tagging in the vesicle<\/li>\r\n \t<li>synthesis of the protein on the lysosome; tagging in the Golgi; packaging in the vesicle; distribution in the endoplasmic reticulum<\/li>\r\n \t<li>synthesis of the protein on the ribosome; modification in the endoplasmic reticulum; tagging in the Golgi; distribution via the vesicle<\/li>\r\n \t<li>synthesis of the protein on the lysosome; packaging in the vesicle; distribution via the Golgi; tagging in the endoplasmic reticulum<\/li>\r\n<\/ol>\r\n<\/div>\r\n[reveal-answer q=\"fs-id1869947\"]Show Solution[\/reveal-answer]\r\n[hidden-answer a=\"fs-id1869947\"]\r\n<div id=\"fs-id1869947\">\r\n\r\nC\r\n\r\n<\/div>\r\n[\/hidden-answer]\r\n\r\n<\/div>\r\n<div id=\"fs-idm71000711\">\r\n<div id=\"fs-idp81418438\">\r\n<p id=\"fs-idm74380423\">Congenital disorders of glycosylation are a growing class of rare diseases. Which organelle would be most commonly involved in the glycoprotein disorder portion of the group?<\/p>\r\n\r\n<ol id=\"fs-idm67922762\" type=\"a\">\r\n \t<li>RER<\/li>\r\n \t<li>ribosomes<\/li>\r\n \t<li>endosomes<\/li>\r\n \t<li>Golgi apparatus<\/li>\r\n<\/ol>\r\n<\/div>\r\n[reveal-answer q=\"fs-idm40512366\"]Show Solution[\/reveal-answer]\r\n[hidden-answer a=\"fs-idm40512366\"]\r\n<div id=\"fs-idm40512366\">\r\n<p id=\"fs-idm200102072\">D<\/p>\r\n\r\n<\/div>\r\n[\/hidden-answer]\r\n\r\n<\/div>\r\n<\/div>\r\n<div class=\"free-response textbox exercises\">\r\n<h3>Free Response<\/h3>\r\n<div id=\"fs-id1755641\">\r\n<div id=\"fs-id2056365\">\r\n<p id=\"fs-id1965223\">In the context of cell biology, what do we mean by form follows function? What are at least two examples of this concept?<\/p>\r\n\r\n<\/div>\r\n[reveal-answer q=\"fs-id1953693\"]Show Solution[\/reveal-answer]\r\n[hidden-answer a=\"fs-id1953693\"]\r\n<div id=\"fs-id1953693\">\r\n<p id=\"fs-id1722854\">\u201cForm follows function\u201d refers to the idea that the function of a body part dictates the form of that body part. As an example, compare your arm to a bat\u2019s wing. While the bones of the two correspond, the parts serve different functions in each organism and their forms have adapted to follow that function.<\/p>\r\n\r\n<\/div>\r\n[\/hidden-answer]\r\n\r\n<\/div>\r\n<div id=\"fs-id1961754\">\r\n<div id=\"fs-id2068069\">\r\n<p id=\"fs-id1848396\">In your opinion, is the nuclear membrane part of the endomembrane system? Why or why not? Defend your answer.<\/p>\r\n\r\n<\/div>\r\n[reveal-answer q=\"fs-id2190555\"]Show Solution[\/reveal-answer]\r\n[hidden-answer a=\"fs-id2190555\"]\r\n<div id=\"fs-id2190555\">\r\n<p id=\"fs-id1466466\">Since the external surface of the nuclear membrane is continuous with the rough endoplasmic reticulum, which is part of the endomembrane system, then it is correct to say that it is part of the system.<\/p>\r\n\r\n<\/div>\r\n[\/hidden-answer]\r\n\r\n<\/div>\r\n<\/div>\r\n<div class=\"textbox shaded\">\r\n<h3>Glossary<\/h3>\r\n<dl id=\"fs-id1686927\">\r\n \t<dt>endomembrane system<\/dt>\r\n \t<dd id=\"fs-id1715595\">group of organelles and membranes in eukaryotic cells that work together modifying, packaging, and transporting lipids and proteins<\/dd>\r\n<\/dl>\r\n<dl id=\"fs-id1769701\">\r\n \t<dt>endoplasmic reticulum (ER)<\/dt>\r\n \t<dd id=\"fs-id2005605\">series of interconnected membranous structures within eukaryotic cells that collectively modify proteins and synthesize lipids<\/dd>\r\n<\/dl>\r\n<dl id=\"fs-id1438096\">\r\n \t<dt>Golgi apparatus<\/dt>\r\n \t<dd id=\"fs-id1454036\">eukaryotic organelle comprised of a series of stacked membranes that sorts, tags, and packages lipids and proteins for distribution<\/dd>\r\n<\/dl>\r\n<dl>\r\n \t<dt>rough endoplasmic reticulum (RER)<\/dt>\r\n \t<dd id=\"fs-id1699690\">region of the endoplasmic reticulum that is studded with ribosomes and engages in protein modification and phospholipid synthesis<\/dd>\r\n<\/dl>\r\n<dl id=\"fs-id1954356\">\r\n \t<dt>smooth endoplasmic reticulum (SER)<\/dt>\r\n \t<dd id=\"fs-id1722834\">region of the endoplasmic reticulum that has few or no ribosomes on its cytoplasmic surface and synthesizes carbohydrates, lipids, and steroid hormones; detoxifies certain chemicals (like pesticides, preservatives, medications, and environmental pollutants), and stores calcium ions<\/dd>\r\n<\/dl>\r\n<\/div>","rendered":"<div class=\"textbox learning-objectives\">\n<h3>Learning Objectives<\/h3>\n<p>By the end of this section, you will be able to do the following:<\/p>\n<ul>\n<li>List the components of the endomembrane system<\/li>\n<li>Recognize the relationship between the endomembrane system and its functions<\/li>\n<\/ul>\n<\/div>\n<p id=\"fs-id1443008\">The endomembrane system (endo = \u201cwithin\u201d) is a group of membranes and organelles (<a class=\"autogenerated-content\" href=\"#fig-ch04-04-01\">(Figure)<\/a>) in eukaryotic cells that works together to modify, package, and transport lipids and proteins. It includes the nuclear envelope, lysosomes, and vesicles, which we have already mentioned, and the endoplasmic reticulum and Golgi apparatus, which we will cover shortly. Although not technically <em>within<\/em> the cell, the plasma membrane is included in the endomembrane system because, as you will see, it interacts with the other endomembranous organelles. The endomembrane system does not include either mitochondria or chloroplast membranes.<\/p>\n<div id=\"fs-id1721886\">\n<div class=\"textbox examples\">\n<h3>Art Connection<\/h3>\n<div style=\"width: 360px\" class=\"wp-caption aligncenter\"><img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/3206\/2018\/05\/03174630\/Figure_04_04_01.png\" alt=\"The left part of this figure shows the rough ER with an integral membrane protein embedded in it. The part of the protein facing the inside of the ER has a carbohydrate attached to it. The protein is shown leaving the ER in a vesicle that fuses with the cis side of the Golgi apparatus. The Golgi apparatus consists of several layers of membranes, called cisternae. As the protein passes through the cisternae, it is further modified by the addition of more carbohydrates. Eventually, it leaves the trans face of the Golgi in a vesicle. The vesicle fuses with the cell membrane so that the carbohydrate that was on the inside of the vesicle now faces the outside of the membrane. At the same time, the contents of the vesicle are ejected from the cell.\" width=\"350\" height=\"835\" \/><\/p>\n<p class=\"wp-caption-text\"><strong>Figure 1. <\/strong>Membrane and secretory proteins are synthesized in the rough endoplasmic reticulum (RER). The RER also sometimes modifies proteins. In this illustration, an attachment of a (purple) carbohydrate modifies a (green) integral membrane protein in the ER. Vesicles with the integral protein bud from the ER and fuse with the Golgi apparatus&#8217; cis face. As the protein passes along the Golgi\u2019s cisternae, the addition of more carbohydrates further modifies it. After its synthesis is complete, it exits as an integral membrane protein of the vesicle that buds from the Golgi\u2019s <strong>trans<\/strong> face. When the vesicle fuses with the cell membrane, the protein becomes an integral portion of that cell membrane. (credit: modification of work by Magnus Manske)<\/p>\n<\/div>\n<p>If a peripheral membrane protein were synthesized in the lumen (inside) of the ER, would it end up on the inside or outside of the plasma membrane?<\/p>\n<\/div>\n<\/div>\n<div id=\"fs-id2028479\" class=\"bc-section section\">\n<h3>The Endoplasmic Reticulum<\/h3>\n<p id=\"fs-id1775048\">The endoplasmic reticulum (ER) (<a class=\"autogenerated-content\" href=\"#fig-ch04-04-01\">(Figure)<\/a>) is a series of interconnected membranous sacs and tubules that collectively modifies proteins and synthesizes lipids. However, these two functions take place in separate areas of the ER: the rough ER and the smooth ER, respectively.<\/p>\n<p>We call the ER tubules&#8217; hollow portion the lumen or cisternal space. The ER&#8217;s membrane, which is a phospholipid bilayer embedded with proteins, is continuous with the nuclear envelope.<\/p>\n<div id=\"fs-id1234002\" class=\"bc-section section\">\n<h4>Rough ER<\/h4>\n<p id=\"fs-id1207356\">Scientists have named the rough endoplasmic reticulum (RER) as such because the ribosomes attached to its cytoplasmic surface give it a studded appearance when viewing it through an electron microscope (<a class=\"autogenerated-content\" href=\"#fig-ch04-04-02\">(Figure)<\/a>).<\/p>\n<div id=\"fig-ch04-04-02\" class=\"wp-caption aligncenter\">\n<div style=\"width: 360px\" class=\"wp-caption aligncenter\"><img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/3206\/2018\/05\/03174634\/Figure_04_04_02_new.jpg\" alt=\"In this transmission electron micrograph, the nucleus is the most prominent feature. The nucleolus is a circular, dark region inside the nucleus. A nuclear pore can be seen in the nuclear envelope that surrounds the nucleus. The rough endoplasmic reticulum surrounds the nucleus, appearing as many layers of membranes. A mitochondrion sits between the layers of the ER membrane.\" width=\"350\" height=\"257\" \/><\/p>\n<p class=\"wp-caption-text\"><strong>Figure 2. <\/strong>This transmission electron micrograph shows the rough endoplasmic reticulum and other organelles in a pancreatic cell. (credit: modification of work by Louisa Howard)<\/p>\n<\/div>\n<\/div>\n<p>Ribosomes transfer their newly synthesized proteins into the RER&#8217;s lumen where they undergo structural modifications, such as folding or acquiring side chains. These modified proteins incorporate into cellular membranes\u2014the ER or the ER&#8217;s or other organelles&#8217; membranes. The proteins can also secrete from the cell (such as protein hormones, enzymes). The RER also makes phospholipids for cellular membranes.<\/p>\n<p id=\"fs-id1752751\">If the phospholipids or modified proteins are not destined to stay in the RER, they will reach their destinations via transport vesicles that bud from the RER\u2019s membrane (<a class=\"autogenerated-content\" href=\"#fig-ch04-04-01\">(Figure)<\/a>).<\/p>\n<p id=\"fs-id2028331\">Since the RER is engaged in modifying proteins (such as enzymes, for example) that secrete from the cell, you would be correct in assuming that the RER is abundant in cells that secrete proteins. This is the case with liver cells, for example.<\/p>\n<\/div>\n<div id=\"fs-id1603907\" class=\"bc-section section\">\n<h4>Smooth ER<\/h4>\n<p id=\"fs-id1459714\">The smooth endoplasmic reticulum (SER) is continuous with the RER but has few or no ribosomes on its cytoplasmic surface (<a class=\"autogenerated-content\" href=\"#fig-ch04-04-01\">(Figure)<\/a>). SER functions include synthesis of carbohydrates, lipids, and steroid hormones; detoxification of medications and poisons; and storing calcium ions.<\/p>\n<p id=\"fs-id1303729\">In muscle cells, a specialized SER, the sarcoplasmic reticulum, is responsible for storing calcium ions that are needed to trigger the muscle cells&#8217; coordinated contractions.<\/p>\n<div class=\"interactive textbox tryit\">\n<h3>Link to Learning<\/h3>\n<p id=\"fs-id2215743\">You can watch an excellent animation of the endomembrane system <a href=\"http:\/\/openstax.org\/l\/insane_in_the_endomembrane\" target=\"_window\">here<\/a>. At the end of the animation, there is a short self-assessment.<\/p>\n<\/div>\n<div id=\"fs-id1912861\" class=\"career textbox examples\">\n<h3>Career Connection<\/h3>\n<p><strong>Cardiologist<\/strong><\/p>\n<p>Heart disease is the leading cause of death in the United States. This is primarily due to our sedentary lifestyle and our high trans-fat diets.<\/p>\n<p>Heart failure is just one of many disabling heart conditions. Heart failure does not mean that the heart has stopped working. Rather, it means that the heart can\u2019t pump with sufficient force to transport oxygenated blood to all the vital organs. Left untreated, heart failure can lead to kidney failure and other organ failure.<\/p>\n<p>Cardiac muscle tissue comprises the heart&#8217;s wall. Heart failure occurs when cardiac muscle cells&#8217; endoplasmic reticula do not function properly. As a result, an insufficient number of calcium ions are available to trigger a sufficient contractile force.<\/p>\n<p id=\"fs-id1430174\">Cardiologists (cardi- = \u201cheart\u201d; -ologist = \u201cone who studies\u201d) are doctors who specialize in treating heart diseases, including heart failure. Cardiologists can diagnose heart failure via a physical examination, results from an electrocardiogram (ECG, a test that measures the heart&#8217;s electrical activity), a chest X-ray to see whether the heart is enlarged, and other tests. If the cardiologist diagnoses heart failure, he or she will typically prescribe appropriate medications and recommend a reduced table salt intake and a supervised exercise program.<\/p>\n<\/div>\n<\/div>\n<\/div>\n<div id=\"fs-id1664568\" class=\"bc-section section\">\n<h3>The Golgi Apparatus<\/h3>\n<p id=\"fs-id1340070\">We have already mentioned that vesicles can bud from the ER and transport their contents elsewhere, but where do the vesicles go? Before reaching their final destination, the lipids or proteins within the transport vesicles still need sorting, packaging, and tagging so that they end up in the right place. Sorting, tagging, packaging, and distributing lipids and proteins takes place in the Golgi apparatus (also called the Golgi body), a series of flattened membranes (<a class=\"autogenerated-content\" href=\"#fig-ch04-04-03\">(Figure)<\/a>).<\/p>\n<div id=\"fig-ch04-04-03\" class=\"wp-caption aligncenter\">\n<div style=\"width: 360px\" class=\"wp-caption aligncenter\"><img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/3206\/2018\/05\/03174636\/Figure_04_04_03.jpg\" alt=\"In this transmission electron micrograph, the Golgi apparatus appears as a stack of membranes surrounded by unnamed organelles.\" width=\"350\" height=\"275\" \/><\/p>\n<p class=\"wp-caption-text\"><strong>Figure 3. <\/strong>The Golgi apparatus in this white blood cell is visible as a stack of semicircular, flattened rings in the lower portion of the image. You can see several vesicles near the Golgi apparatus. (credit: modification of work by Louisa Howard)<\/p>\n<\/div>\n<\/div>\n<p id=\"fs-id1726293\">We call the Golgi apparatus&#8217; the <em>cis<\/em> face. The opposite side is the <em>trans<\/em> face. The transport vesicles that formed from the ER travel to the <em>cis<\/em> face, fuse with it, and empty their contents into the Golgi apparatus&#8217; lumen. As the proteins and lipids travel through the Golgi, they undergo further modifications that allow them to be sorted. The most frequent modification is adding short sugar molecule chains. These newly modified proteins and lipids then tag with phosphate groups or other small molecules in order to travel to their proper destinations.<\/p>\n<p id=\"fs-id1716512\">Finally, the modified and tagged proteins are packaged into secretory vesicles that bud from the Golgi&#8217;s <em>trans<\/em> face. While some of these vesicles deposit their contents into other cell parts where they will be used, other secretory vesicles fuse with the plasma membrane and release their contents outside the cell.<\/p>\n<p>In another example of form following function, cells that engage in a great deal of secretory activity (such as salivary gland cells that secrete digestive enzymes or immune system cells that secrete antibodies) have an abundance of Golgi.<\/p>\n<p id=\"fs-id1006507\">In plant cells, the Golgi apparatus has the additional role of synthesizing polysaccharides, some of which are incorporated into the cell wall and some of which other cell parts use.<\/p>\n<div id=\"fs-id1618891\" class=\"career textbox examples\">\n<h3>Career Connection<\/h3>\n<p id=\"fs-id2358461\"><strong>Geneticist<\/strong><\/p>\n<p>Many diseases arise from genetic mutations that prevent synthesizing critical proteins. One such disease is Lowe disease (or oculocerebrorenal syndrome, because it affects the eyes, brain, and kidneys). In Lowe disease, there is a deficiency in an enzyme localized to the Golgi apparatus. Children with Lowe disease are born with cataracts, typically develop kidney disease after the first year of life, and may have impaired mental abilities.<\/p>\n<p id=\"fs-id1993778\">A mutation on the X chromosome causes Lowe disease. The X chromosome is one of the two human sex chromosomes, as these chromosomes determine a person&#8217;s sex. Females possess two X chromosomes while males possess one X and one Y chromosome. In females, the genes on only one of the two X chromosomes are expressed. Females who carry the Lowe disease gene on one of their X chromosomes are carriers and do not show symptoms of the disease. However, males only have one X chromosome and the genes on this chromosome are always expressed. Therefore, males will always have Lowe disease if their X chromosome carries the Lowe disease gene. Geneticists have identified the mutated gene&#8217;s location, as well as many other mutation locations that cause genetic diseases. Through prenatal testing, a woman can find out if the fetus she is carrying may be afflicted with one of several genetic diseases.<\/p>\n<p id=\"fs-id1126762\">Geneticists analyze prenatal genetic test results and may counsel pregnant women on available options. They may also conduct genetic research that leads to new drugs or foods, or perform DNA analyses for forensic investigations.<\/p>\n<\/div>\n<\/div>\n<div id=\"fs-id1482669\" class=\"bc-section section\">\n<h3>Lysosomes<\/h3>\n<p id=\"fs-id1986769\">In addition to their role as the digestive component and organelle-recycling facility of animal cells, lysosomes are part of the endomembrane system. Lysosomes also use their hydrolytic enzymes to destroy pathogens (disease-causing organisms) that might enter the cell. A good example of this occurs in macrophages, a group of white blood cells which are part of your body\u2019s immune system. In a process that scientists call phagocytosis or endocytosis, a section of the macrophage&#8217;s plasma membrane invaginates (folds in) and engulfs a pathogen. The invaginated section, with the pathogen inside, then pinches itself off from the plasma membrane and becomes a vesicle. The vesicle fuses with a lysosome. The lysosome\u2019s hydrolytic enzymes then destroy the pathogen (<a class=\"autogenerated-content\" href=\"#fig-ch04-04-04\">(Figure)<\/a>).<\/p>\n<div id=\"fig-ch04-04-04\" class=\"wp-caption aligncenter\">\n<div style=\"width: 460px\" class=\"wp-caption aligncenter\"><img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/3206\/2018\/05\/03174641\/Figure_04_04_04.png\" alt=\"In this illustration, a eukaryotic cell is shown consuming a bacterium. As the bacterium is consumed, it is encapsulated in a vesicle. The vesicle fuses with a lysosome, and proteins inside the lysosome digest the bacterium.\" width=\"450\" height=\"1097\" \/><\/p>\n<p class=\"wp-caption-text\"><strong>Figure 4. <\/strong>A macrophage has engulfed (phagocytized) a potentially pathogenic bacterium and then fuses with lysosomes within the cell to destroy the pathogen. Other organelles are present in the cell but for simplicity we do not show them.<\/p>\n<\/div>\n<\/div>\n<\/div>\n<div id=\"fs-id1687072\" class=\"summary textbox key-takeaways\">\n<h3>Section Summary<\/h3>\n<p>The endomembrane system includes the nuclear envelope, lysosomes, vesicles, the ER, and Golgi apparatus, as well as the plasma membrane. These cellular components work together to modify, package, tag, and transport proteins and lipids that form the membranes.<\/p>\n<p>The RER modifies proteins and synthesizes phospholipids in cell membranes. The SER synthesizes carbohydrates, lipids, and steroid hormones; engages in the detoxification of medications and poisons; and stores calcium ions. Sorting, tagging, packaging, and distributing lipids and proteins take place in the Golgi apparatus. Budding RER and Golgi membranes create lysosomes. Lysosomes digest macromolecules, recycle worn-out organelles, and destroy pathogens.<\/p>\n<\/div>\n<div id=\"fs-id2075509\" class=\"art-exercise\">\n<h3>Art Connections<\/h3>\n<div id=\"fs-id1570796\">\n<div id=\"fs-id1879455\">\n<p id=\"fs-id1416538\"><a class=\"autogenerated-content\" href=\"#fig-ch04-04-01\">(Figure)<\/a> If a peripheral membrane protein were synthesized in the lumen (inside) of the ER, would it end up on the inside or outside of the plasma membrane?<\/p>\n<\/div>\n<div>\n<p id=\"fs-id1722059\">\n<div class=\"qa-wrapper\" style=\"display: block\"><span class=\"show-answer collapsed\" style=\"cursor: pointer\" data-target=\"q305623\">Show Solution<\/span><\/p>\n<div id=\"q305623\" class=\"hidden-answer\" style=\"display: none\">\n<p><a href=\"#fig-ch04-04-01\">(Figure)<\/a> It would end up on the outside. After the vesicle passes through the Golgi apparatus and fuses with the plasma membrane, it turns inside out.<\/div>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n<div id=\"fs-id1904682\" class=\"multiple-choice textbox exercises\">\n<h3>Review Questions<\/h3>\n<div id=\"fs-id1486983\">\n<div>\n<p id=\"fs-id2029669\">Which of the following is not a component of the endomembrane system?<\/p>\n<ol id=\"fs-id2215260\" type=\"a\">\n<li>mitochondrion<\/li>\n<li>Golgi apparatus<\/li>\n<li>endoplasmic reticulum<\/li>\n<li>lysosome<\/li>\n<\/ol>\n<\/div>\n<div class=\"qa-wrapper\" style=\"display: block\"><span class=\"show-answer collapsed\" style=\"cursor: pointer\" data-target=\"qfs-id1970249\">Show Solution<\/span><\/p>\n<div id=\"qfs-id1970249\" class=\"hidden-answer\" style=\"display: none\">\n<div id=\"fs-id1970249\">\n<p id=\"fs-id2027385\">A<\/p>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n<div>\n<div id=\"fs-id1987167\">\n<p id=\"fs-id1806761\">The process by which a cell engulfs a foreign particle is known as:<\/p>\n<ol id=\"fs-id1316992\" type=\"a\">\n<li>endosymbiosis<\/li>\n<li>phagocytosis<\/li>\n<li>hydrolysis<\/li>\n<li>membrane synthesis<\/li>\n<\/ol>\n<\/div>\n<div class=\"qa-wrapper\" style=\"display: block\"><span class=\"show-answer collapsed\" style=\"cursor: pointer\" data-target=\"qfs-id2025979\">Show Solution<\/span><\/p>\n<div id=\"qfs-id2025979\" class=\"hidden-answer\" style=\"display: none\">\n<div id=\"fs-id2025979\">\n<p id=\"fs-id1774676\">B<\/p>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n<div>\n<div id=\"fs-id1734531\">\n<p>Which of the following is most likely to have the greatest concentration of smooth endoplasmic reticulum?<\/p>\n<ol id=\"fs-id1735841\" type=\"a\">\n<li>a cell that secretes enzymes<\/li>\n<li>a cell that destroys pathogens<\/li>\n<li>a cell that makes steroid hormones<\/li>\n<li>a cell that engages in photosynthesis<\/li>\n<\/ol>\n<\/div>\n<div class=\"qa-wrapper\" style=\"display: block\"><span class=\"show-answer collapsed\" style=\"cursor: pointer\" data-target=\"qfs-id1386336\">Show Solution<\/span><\/p>\n<div id=\"qfs-id1386336\" class=\"hidden-answer\" style=\"display: none\">\n<div id=\"fs-id1386336\">\n<p id=\"fs-id2367542\">C<\/p>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n<div id=\"fs-id1703517\">\n<div>\n<p>Which of the following sequences correctly lists in order the steps involved in the incorporation of a proteinaceous molecule within a cell?<\/p>\n<ol id=\"fs-id1644310\" type=\"a\">\n<li>protein synthesis of the protein on the ribosome; modification in the Golgi apparatus; packaging in the endoplasmic reticulum; tagging in the vesicle<\/li>\n<li>synthesis of the protein on the lysosome; tagging in the Golgi; packaging in the vesicle; distribution in the endoplasmic reticulum<\/li>\n<li>synthesis of the protein on the ribosome; modification in the endoplasmic reticulum; tagging in the Golgi; distribution via the vesicle<\/li>\n<li>synthesis of the protein on the lysosome; packaging in the vesicle; distribution via the Golgi; tagging in the endoplasmic reticulum<\/li>\n<\/ol>\n<\/div>\n<div class=\"qa-wrapper\" style=\"display: block\"><span class=\"show-answer collapsed\" style=\"cursor: pointer\" data-target=\"qfs-id1869947\">Show Solution<\/span><\/p>\n<div id=\"qfs-id1869947\" class=\"hidden-answer\" style=\"display: none\">\n<div id=\"fs-id1869947\">\n<p>C<\/p>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n<div id=\"fs-idm71000711\">\n<div id=\"fs-idp81418438\">\n<p id=\"fs-idm74380423\">Congenital disorders of glycosylation are a growing class of rare diseases. Which organelle would be most commonly involved in the glycoprotein disorder portion of the group?<\/p>\n<ol id=\"fs-idm67922762\" type=\"a\">\n<li>RER<\/li>\n<li>ribosomes<\/li>\n<li>endosomes<\/li>\n<li>Golgi apparatus<\/li>\n<\/ol>\n<\/div>\n<div class=\"qa-wrapper\" style=\"display: block\"><span class=\"show-answer collapsed\" style=\"cursor: pointer\" data-target=\"qfs-idm40512366\">Show Solution<\/span><\/p>\n<div id=\"qfs-idm40512366\" class=\"hidden-answer\" style=\"display: none\">\n<div id=\"fs-idm40512366\">\n<p id=\"fs-idm200102072\">D<\/p>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n<div class=\"free-response textbox exercises\">\n<h3>Free Response<\/h3>\n<div id=\"fs-id1755641\">\n<div id=\"fs-id2056365\">\n<p id=\"fs-id1965223\">In the context of cell biology, what do we mean by form follows function? What are at least two examples of this concept?<\/p>\n<\/div>\n<div class=\"qa-wrapper\" style=\"display: block\"><span class=\"show-answer collapsed\" style=\"cursor: pointer\" data-target=\"qfs-id1953693\">Show Solution<\/span><\/p>\n<div id=\"qfs-id1953693\" class=\"hidden-answer\" style=\"display: none\">\n<div id=\"fs-id1953693\">\n<p id=\"fs-id1722854\">\u201cForm follows function\u201d refers to the idea that the function of a body part dictates the form of that body part. As an example, compare your arm to a bat\u2019s wing. While the bones of the two correspond, the parts serve different functions in each organism and their forms have adapted to follow that function.<\/p>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n<div id=\"fs-id1961754\">\n<div id=\"fs-id2068069\">\n<p id=\"fs-id1848396\">In your opinion, is the nuclear membrane part of the endomembrane system? Why or why not? Defend your answer.<\/p>\n<\/div>\n<div class=\"qa-wrapper\" style=\"display: block\"><span class=\"show-answer collapsed\" style=\"cursor: pointer\" data-target=\"qfs-id2190555\">Show Solution<\/span><\/p>\n<div id=\"qfs-id2190555\" class=\"hidden-answer\" style=\"display: none\">\n<div id=\"fs-id2190555\">\n<p id=\"fs-id1466466\">Since the external surface of the nuclear membrane is continuous with the rough endoplasmic reticulum, which is part of the endomembrane system, then it is correct to say that it is part of the system.<\/p>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n<div class=\"textbox shaded\">\n<h3>Glossary<\/h3>\n<dl id=\"fs-id1686927\">\n<dt>endomembrane system<\/dt>\n<dd id=\"fs-id1715595\">group of organelles and membranes in eukaryotic cells that work together modifying, packaging, and transporting lipids and proteins<\/dd>\n<\/dl>\n<dl id=\"fs-id1769701\">\n<dt>endoplasmic reticulum (ER)<\/dt>\n<dd id=\"fs-id2005605\">series of interconnected membranous structures within eukaryotic cells that collectively modify proteins and synthesize lipids<\/dd>\n<\/dl>\n<dl id=\"fs-id1438096\">\n<dt>Golgi apparatus<\/dt>\n<dd id=\"fs-id1454036\">eukaryotic organelle comprised of a series of stacked membranes that sorts, tags, and packages lipids and proteins for distribution<\/dd>\n<\/dl>\n<dl>\n<dt>rough endoplasmic reticulum (RER)<\/dt>\n<dd id=\"fs-id1699690\">region of the endoplasmic reticulum that is studded with ribosomes and engages in protein modification and phospholipid synthesis<\/dd>\n<\/dl>\n<dl id=\"fs-id1954356\">\n<dt>smooth endoplasmic reticulum (SER)<\/dt>\n<dd id=\"fs-id1722834\">region of the endoplasmic reticulum that has few or no ribosomes on its cytoplasmic surface and synthesizes carbohydrates, lipids, and steroid hormones; detoxifies certain chemicals (like pesticides, preservatives, medications, and environmental pollutants), and stores calcium ions<\/dd>\n<\/dl>\n<\/div>\n\n\t\t\t <section class=\"citations-section\" role=\"contentinfo\">\n\t\t\t <h3>Candela Citations<\/h3>\n\t\t\t\t\t <div>\n\t\t\t\t\t\t <div id=\"citation-list-571\">\n\t\t\t\t\t\t\t <div class=\"licensing\"><div class=\"license-attribution-dropdown-subheading\">CC licensed content, Shared previously<\/div><ul class=\"citation-list\"><li>Biology 2e. <strong>Provided by<\/strong>: OpenStax. <strong>Located at<\/strong>: <a target=\"_blank\" href=\"https:\/\/openstax.org\/details\/books\/biology-2e\">https:\/\/openstax.org\/details\/books\/biology-2e<\/a>. <strong>License<\/strong>: <em><a target=\"_blank\" rel=\"license\" href=\"https:\/\/creativecommons.org\/licenses\/by\/4.0\/\">CC BY: Attribution<\/a><\/em>. <strong>License Terms<\/strong>: Download for free at http:\/\/cnx.org\/contents\/8d50a0af-948b-4204-a71d-4826cba765b8@8.19<\/li><\/ul><\/div>\n\t\t\t\t\t\t <\/div>\n\t\t\t\t\t <\/div>\n\t\t\t <\/section>","protected":false},"author":311,"menu_order":5,"template":"","meta":{"_candela_citation":"[{\"type\":\"cc\",\"description\":\"Biology 2e\",\"author\":\"\",\"organization\":\"OpenStax\",\"url\":\"https:\/\/openstax.org\/details\/books\/biology-2e\",\"project\":\"\",\"license\":\"cc-by\",\"license_terms\":\"Download for free at http:\/\/cnx.org\/contents\/8d50a0af-948b-4204-a71d-4826cba765b8@8.19\"}]","CANDELA_OUTCOMES_GUID":"","pb_show_title":"on","pb_short_title":"","pb_subtitle":"","pb_authors":[],"pb_section_license":""},"chapter-type":[],"contributor":[],"license":[],"class_list":["post-571","chapter","type-chapter","status-publish","hentry"],"part":542,"_links":{"self":[{"href":"https:\/\/courses.lumenlearning.com\/suny-osbiology2e\/wp-json\/pressbooks\/v2\/chapters\/571","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/courses.lumenlearning.com\/suny-osbiology2e\/wp-json\/pressbooks\/v2\/chapters"}],"about":[{"href":"https:\/\/courses.lumenlearning.com\/suny-osbiology2e\/wp-json\/wp\/v2\/types\/chapter"}],"author":[{"embeddable":true,"href":"https:\/\/courses.lumenlearning.com\/suny-osbiology2e\/wp-json\/wp\/v2\/users\/311"}],"version-history":[{"count":3,"href":"https:\/\/courses.lumenlearning.com\/suny-osbiology2e\/wp-json\/pressbooks\/v2\/chapters\/571\/revisions"}],"predecessor-version":[{"id":2446,"href":"https:\/\/courses.lumenlearning.com\/suny-osbiology2e\/wp-json\/pressbooks\/v2\/chapters\/571\/revisions\/2446"}],"part":[{"href":"https:\/\/courses.lumenlearning.com\/suny-osbiology2e\/wp-json\/pressbooks\/v2\/parts\/542"}],"metadata":[{"href":"https:\/\/courses.lumenlearning.com\/suny-osbiology2e\/wp-json\/pressbooks\/v2\/chapters\/571\/metadata\/"}],"wp:attachment":[{"href":"https:\/\/courses.lumenlearning.com\/suny-osbiology2e\/wp-json\/wp\/v2\/media?parent=571"}],"wp:term":[{"taxonomy":"chapter-type","embeddable":true,"href":"https:\/\/courses.lumenlearning.com\/suny-osbiology2e\/wp-json\/pressbooks\/v2\/chapter-type?post=571"},{"taxonomy":"contributor","embeddable":true,"href":"https:\/\/courses.lumenlearning.com\/suny-osbiology2e\/wp-json\/wp\/v2\/contributor?post=571"},{"taxonomy":"license","embeddable":true,"href":"https:\/\/courses.lumenlearning.com\/suny-osbiology2e\/wp-json\/wp\/v2\/license?post=571"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}