{"id":786,"date":"2017-08-30T14:36:44","date_gmt":"2017-08-30T18:36:44","guid":{"rendered":"https:\/\/pressbooks.bccampus.ca\/dcbiol11031109\/chapter\/3-2-the-cytoplasm-and-cellular-organelles\/"},"modified":"2018-06-23T15:53:17","modified_gmt":"2018-06-23T19:53:17","slug":"3-2-the-cytoplasm-and-cellular-organelles","status":"publish","type":"chapter","link":"https:\/\/pressbooks.bccampus.ca\/dcbiol11031109\/chapter\/3-2-the-cytoplasm-and-cellular-organelles\/","title":{"raw":"3.2 The Cytoplasm and Cellular Organelles","rendered":"3.2 The Cytoplasm and Cellular Organelles"},"content":{"raw":"<div class=\"bcc-box bcc-highlight\">\r\n<h3>Learning Objectives<\/h3>\r\nBy the end of this section, you will be able to:\r\n<ul>\r\n \t<li>Describe the structure and function of the cellular organelles associated with the endomembrane system, including the endoplasmic reticulum, Golgi apparatus, vesicles, and lysosomes<\/li>\r\n \t<li>Describe the structure and function of ribosomes<\/li>\r\n \t<li>Describe the structure and function of mitochondria<\/li>\r\n<\/ul>\r\n<\/div>\r\n\r\n[caption id=\"\" align=\"aligncenter\" width=\"450\"]<img src=\"https:\/\/pressbooks.bccampus.ca\/dcbiol11031109\/wp-content\/uploads\/sites\/149\/2017\/08\/0312_Animal_Cell_and_Components-3.jpg\" alt=\"This diagram shows an animal cell with all the intracellular organelles labeled.\" width=\"450\" height=\"645\" style=\"color: initial\" \/> Figure 1. Prototypical Human Cell. While this image is not indicative of any one particular human cell, it is a prototypical example of a cell containing the primary organelles and internal structures.[\/caption]\r\n\r\nNow that you have learned that the cell membrane surrounds all cells, you can dive inside of a prototypical human cell to learn about its internal components and their functions. All living cells in multicellular organisms contain an internal cytoplasmic compartment, and a nucleus within the cytoplasm. <strong>Cytosol<\/strong>, the jelly-like substance within the cell, provides the fluid medium necessary for biochemical reactions. Eukaryotic cells, including all animal cells, also contain various cellular organelles. An <strong>organelle<\/strong> (\u201clittle organ\u201d) is one of several different types of membrane-enclosed bodies in the cell, each performing a unique function. Just as the various bodily organs work together in harmony to perform all of a human\u2019s functions, the many different cellular organelles work together to keep the cell healthy and performing all of its important functions. The organelles and cytosol, taken together, compose the cell\u2019s <strong>cytoplasm<\/strong>. The <strong>nucleus<\/strong> is a cell\u2019s central organelle, which contains the cell\u2019s DNA (<a class=\"autogenerated-content\" href=\"#fig-ch03_02_01\">Figure 1<\/a>).\r\n<figure id=\"fig-ch03_02_01\"><figcaption><\/figcaption><\/figure>\r\n<section id=\"fs-id1331186\">\r\n<h1>Organelles of the Endomembrane System<\/h1>\r\n<p id=\"fs-id1091621\">A set of three major organelles together form a system within the cell called the endomembrane system. These organelles work together to perform various cellular jobs, including the task of producing, packaging, and exporting certain cellular products. The organelles of the endomembrane system include the endoplasmic reticulum, Golgi apparatus, and vesicles.<\/p>\r\n\r\n<section id=\"fs-id1751556\">\r\n<h2>Endoplasmic Reticulum<\/h2>\r\n<p id=\"fs-id2132190\">The <strong>endoplasmic reticulum (ER)<\/strong> is a system of channels that is continuous with the nuclear membrane (or \u201cenvelope\u201d) covering the nucleus and composed of the same lipid bilayer material. The ER can be thought of as a series of winding thoroughfares similar to the waterway canals in Venice. The ER provides passages throughout much of the cell that function in transporting, synthesizing, and storing materials. The winding structure of the ER results in a large membranous surface area that supports its many functions (<a class=\"autogenerated-content\" href=\"#fig-ch03_02_02\">Figure 2<\/a>).<\/p>\r\n\r\n<figure id=\"fig-ch03_02_02\"><figcaption>\r\n\r\n[caption id=\"\" align=\"aligncenter\" width=\"550\"]<img src=\"https:\/\/pressbooks.bccampus.ca\/dcbiol11031109\/wp-content\/uploads\/sites\/149\/2017\/08\/0313_Endoplasmic_Reticulum-3.jpg\" alt=\"This figure shows structure of the endoplasmic reticulum. The diagram highlights the rough and smooth endoplasmic reticulum and the nucleus is labeled. Two micrographs show the structure of the endoplasmic reticulum in detail. The left micrograph shows the rough endoplasmic reticulum in a pancreatic cell and the right micrograph shows a smooth endoplasmic reticulum.\" width=\"550\" height=\"892\" \/> Figure 2. Endoplasmic Reticulum (ER). (a) The ER is a winding network of thin membranous sacs found in close association with the cell nucleus. The smooth and rough endoplasmic reticula are very different in appearance and function (source: mouse tissue). (b) Rough ER is studded with numerous ribosomes, which are sites of protein synthesis (source: mouse tissue). EM \u00d7 110,000. (c) Smooth ER synthesizes phospholipids, steroid hormones, regulates the concentration of cellular Ca<sup>2+<\/sup>,metabolizes some carbohydrates, and breaks down certain toxins (source: mouse tissue). EM \u00d7 110,510. (Micrographs provided by the Regents of University of Michigan Medical School \u00a9 2012)[\/caption]\r\n\r\n<\/figcaption><\/figure>\r\n<p id=\"fs-id2552695\">Endoplasmic reticulum can exist in two forms: rough ER and smooth ER. These two types of ER perform some very different functions and can be found in very different amounts depending on the type of cell. Rough ER (RER) is so-called because its membrane is dotted with embedded granules\u2014organelles called ribosomes, giving the RER a bumpy appearance. A <strong>ribosome<\/strong> is an organelle that serves as the site of protein synthesis. It is composed of two ribosomal RNA subunits that wrap around mRNA to start the process of translation, followed by protein synthesis. Smooth ER (SER) lacks these ribosomes.<\/p>\r\n<p id=\"fs-id1858545\">One of the main functions of the smooth ER is in the synthesis of lipids. The smooth ER synthesizes phospholipids, the main component of biological membranes, as well as steroid hormones. For this reason, cells that produce large quantities of such hormones, such as those of the female ovaries and male testes, contain large amounts of smooth ER. In addition to lipid synthesis, the smooth ER also sequesters (i.e., stores) and regulates the concentration of cellular Ca<sup>2+<\/sup>, a function extremely important in cells of the nervous system where Ca<sup>2+<\/sup> is the trigger for neurotransmitter release. The smooth ER additionally metabolizes some carbohydrates and performs a detoxification role, breaking down certain toxins.<\/p>\r\n<p id=\"fs-id2581786\">In contrast with the smooth ER, the primary job of the rough ER is the synthesis and modification of proteins destined for the cell membrane or for export from the cell. For this protein synthesis, many ribosomes attach to the ER (giving it the studded appearance of rough ER). Typically, a protein is synthesized within the ribosome and released inside the channel of the rough ER, where sugars can be added to it (by a process called glycosylation) before it is transported within a <strong>vesicle<\/strong> to the next stage in the packaging and shipping process: the Golgi apparatus.<\/p>\r\n\r\n<\/section><section id=\"fs-id2651407\">\r\n<h2>The Golgi Apparatus<\/h2>\r\nThe <strong>Golgi apparatus<\/strong> is responsible for sorting, modifying, and shipping off the products that come from the rough ER, much like a post-office. The Golgi apparatus looks like stacked flattened discs, almost like stacks of oddly shaped pancakes. Like the ER, these discs are membranous. The Golgi apparatus has two distinct sides, each with a different role. One side of the apparatus receives products in vesicles. These products are sorted through the apparatus, and then they are released from the opposite side after being repackaged into new vesicles. If the product is to be exported from the cell, the vesicle migrates to the cell surface and fuses to the cell membrane, and the cargo is secreted (<a class=\"autogenerated-content\" href=\"#fig-ch03_02_03\">Figure 3<\/a>).\r\n\r\n[caption id=\"\" align=\"aligncenter\" width=\"550\"]<img src=\"https:\/\/pressbooks.bccampus.ca\/dcbiol11031109\/wp-content\/uploads\/sites\/149\/2017\/08\/0314_Golgi_Apparatus-3.jpg\" alt=\"This figure shows the structure of the Golgi apparatus. The diagram in the left panel shows the location and structure of the Golgi apparatus. The right panel shows a micrograph showing the folds of the Golgi in detail.\" width=\"550\" height=\"754\" \/> Figure 3. Golgi Apparatus. (a) The Golgi apparatus manipulates products from the rough ER, and also produces new organelles called lysosomes. Proteins and other products of the ER are sent to the Golgi apparatus, which organizes, modifies, packages, and tags them. Some of these products are transported to other areas of the cell and some are exported from the cell through exocytosis. Enzymatic proteins are packaged as new lysosomes (or packaged and sent for fusion with existing lysosomes). (b) An electron micrograph of the Golgi apparatus.[\/caption]\r\n\r\n<\/section><section id=\"fs-id1661207\">\r\n<h2>Lysosomes<\/h2>\r\n<p id=\"fs-id2027468\">Some of the protein products packaged by the Golgi include digestive enzymes that are meant to remain inside the cell for use in breaking down certain materials. The enzyme-containing vesicles released by the Golgi may form new lysosomes, or fuse with existing, lysosomes. A <strong>lysosome<\/strong> is an organelle that contains enzymes that break down and digest unneeded cellular components, such as a damaged organelle. (A lysosome is similar to a wrecking crew that takes down old and unsound buildings in a neighborhood.) <strong>Autophagy<\/strong> (\u201cself-eating\u201d) is the process of a cell digesting its own structures. Lysosomes are also important for breaking down foreign material. For example, when certain immune defense cells (white blood cells) phagocytize bacteria, the bacterial cell is transported into a lysosome and digested by the enzymes inside. As one might imagine, such phagocytic defense cells contain large numbers of lysosomes.<\/p>\r\n<p id=\"fs-id2549673\">Under certain circumstances, lysosomes perform a more grand and dire function. In the case of damaged or unhealthy cells, lysosomes can be triggered to open up and release their digestive enzymes into the cytoplasm of the cell, killing the cell. This \u201cself-destruct\u201d mechanism is called <strong>autolysis<\/strong>, and makes the process of cell death controlled (a mechanism called \u201capoptosis\u201d).<\/p>\r\nWatch this Khan Academy <a href=\"https:\/\/www.youtube.com\/watch?v=vC-cEWJxDRY\">video<\/a> to learn more about the endomembrane system\r\n\r\n<\/section><\/section><section>\r\n<h1>Organelles for Energy Production<\/h1>\r\n<p id=\"fs-id1988147\">In addition to the jobs performed by the endomembrane system, the cell has many other important functions. Just as you must consume nutrients to provide yourself with energy, so must each of your cells take in nutrient molecules whose chemical energy can be harvested to power biochemical reactions.<\/p>\r\n\r\n<section id=\"fs-id1334972\">\r\n<h2 style=\"text-align: left\">Mitochondria<\/h2>\r\n[caption id=\"\" align=\"aligncenter\" width=\"520\"]<img src=\"https:\/\/pressbooks.bccampus.ca\/dcbiol11031109\/wp-content\/uploads\/sites\/149\/2017\/08\/0315_Mitochondrion_new-3.jpg\" alt=\"This figure shows the structure of a mitochondrion. The inner and outer membrane, the cristae and the intermembrane space are labeled. The right panel shows a micrograph with the structure of a mitochondrion in detail.\" width=\"520\" height=\"991\" \/> Figure 4. Mitochondrion. The mitochondria are the energy-conversion factories of the cell. (a) A mitochondrion is composed of two separate lipid bilayer membranes. Along the inner membrane are various molecules that work together to produce ATP, the cell\u2019s major energy currency. (b) An electron micrograph of mitochondria. EM \u00d7 236,000. (Micrograph provided by the Regents of University of Michigan Medical School \u00a9 2012)[\/caption]\r\n<p id=\"fs-id1692132\">A <strong>mitochondrion<\/strong> (plural = mitochondria) is a membranous, bean-shaped organelle that is the \u201cenergy transformer\u201d of the cell. Mitochondria consist of an outer lipid bilayer membrane as well as an additional inner lipid bilayer membrane (<a class=\"autogenerated-content\" href=\"#fig-ch03_02_04\">Figure 4<\/a>). The inner membrane is highly folded into winding structures with a great deal of surface area, called cristae. It is along this inner membrane that a series of proteins, enzymes, and other molecules perform the biochemical reactions of cellular respiration. These reactions convert energy stored in nutrient molecules (such as glucose) into adenosine triphosphate (ATP), which provides usable cellular energy to the cell. Cells use ATP constantly, and so the mitochondria are constantly at work. Oxygen molecules are required during cellular respiration, which is why you must constantly breathe it in. One of the organ systems in the body that uses huge amounts of ATP is the muscular system because ATP is required to sustain muscle contraction. As a result, muscle cells are packed full of mitochondria. Nerve cells also need large quantities of ATP to run their sodium-potassium pumps. Therefore, an individual neuron will be loaded with over a thousand mitochondria. On the other hand, a bone cell, which is not nearly as metabolically-active, might only have a couple hundred mitochondria.<\/p>\r\n\r\n<\/section><\/section>","rendered":"<div class=\"bcc-box bcc-highlight\">\n<h3>Learning Objectives<\/h3>\n<p>By the end of this section, you will be able to:<\/p>\n<ul>\n<li>Describe the structure and function of the cellular organelles associated with the endomembrane system, including the endoplasmic reticulum, Golgi apparatus, vesicles, and lysosomes<\/li>\n<li>Describe the structure and function of ribosomes<\/li>\n<li>Describe the structure and function of mitochondria<\/li>\n<\/ul>\n<\/div>\n<figure style=\"width: 450px\" class=\"wp-caption aligncenter\"><img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/pressbooks.bccampus.ca\/dcbiol11031109\/wp-content\/uploads\/sites\/149\/2017\/08\/0312_Animal_Cell_and_Components-3.jpg\" alt=\"This diagram shows an animal cell with all the intracellular organelles labeled.\" width=\"450\" height=\"645\" style=\"color: initial\" \/><figcaption class=\"wp-caption-text\">Figure 1. Prototypical Human Cell. While this image is not indicative of any one particular human cell, it is a prototypical example of a cell containing the primary organelles and internal structures.<\/figcaption><\/figure>\n<p>Now that you have learned that the cell membrane surrounds all cells, you can dive inside of a prototypical human cell to learn about its internal components and their functions. All living cells in multicellular organisms contain an internal cytoplasmic compartment, and a nucleus within the cytoplasm. <strong>Cytosol<\/strong>, the jelly-like substance within the cell, provides the fluid medium necessary for biochemical reactions. Eukaryotic cells, including all animal cells, also contain various cellular organelles. An <strong>organelle<\/strong> (\u201clittle organ\u201d) is one of several different types of membrane-enclosed bodies in the cell, each performing a unique function. Just as the various bodily organs work together in harmony to perform all of a human\u2019s functions, the many different cellular organelles work together to keep the cell healthy and performing all of its important functions. The organelles and cytosol, taken together, compose the cell\u2019s <strong>cytoplasm<\/strong>. The <strong>nucleus<\/strong> is a cell\u2019s central organelle, which contains the cell\u2019s DNA (<a class=\"autogenerated-content\" href=\"#fig-ch03_02_01\">Figure 1<\/a>).<\/p>\n<figure id=\"fig-ch03_02_01\"><figcaption><\/figcaption><\/figure>\n<section id=\"fs-id1331186\">\n<h1>Organelles of the Endomembrane System<\/h1>\n<p id=\"fs-id1091621\">A set of three major organelles together form a system within the cell called the endomembrane system. These organelles work together to perform various cellular jobs, including the task of producing, packaging, and exporting certain cellular products. The organelles of the endomembrane system include the endoplasmic reticulum, Golgi apparatus, and vesicles.<\/p>\n<section id=\"fs-id1751556\">\n<h2>Endoplasmic Reticulum<\/h2>\n<p id=\"fs-id2132190\">The <strong>endoplasmic reticulum (ER)<\/strong> is a system of channels that is continuous with the nuclear membrane (or \u201cenvelope\u201d) covering the nucleus and composed of the same lipid bilayer material. The ER can be thought of as a series of winding thoroughfares similar to the waterway canals in Venice. The ER provides passages throughout much of the cell that function in transporting, synthesizing, and storing materials. The winding structure of the ER results in a large membranous surface area that supports its many functions (<a class=\"autogenerated-content\" href=\"#fig-ch03_02_02\">Figure 2<\/a>).<\/p>\n<figure id=\"fig-ch03_02_02\"><figcaption>\n<figure style=\"width: 550px\" class=\"wp-caption aligncenter\"><img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/pressbooks.bccampus.ca\/dcbiol11031109\/wp-content\/uploads\/sites\/149\/2017\/08\/0313_Endoplasmic_Reticulum-3.jpg\" alt=\"This figure shows structure of the endoplasmic reticulum. The diagram highlights the rough and smooth endoplasmic reticulum and the nucleus is labeled. Two micrographs show the structure of the endoplasmic reticulum in detail. The left micrograph shows the rough endoplasmic reticulum in a pancreatic cell and the right micrograph shows a smooth endoplasmic reticulum.\" width=\"550\" height=\"892\" \/><figcaption class=\"wp-caption-text\">Figure 2. Endoplasmic Reticulum (ER). (a) The ER is a winding network of thin membranous sacs found in close association with the cell nucleus. The smooth and rough endoplasmic reticula are very different in appearance and function (source: mouse tissue). (b) Rough ER is studded with numerous ribosomes, which are sites of protein synthesis (source: mouse tissue). EM \u00d7 110,000. (c) Smooth ER synthesizes phospholipids, steroid hormones, regulates the concentration of cellular Ca<sup>2+<\/sup>,metabolizes some carbohydrates, and breaks down certain toxins (source: mouse tissue). EM \u00d7 110,510. (Micrographs provided by the Regents of University of Michigan Medical School \u00a9 2012)<\/figcaption><\/figure>\n<\/figcaption><\/figure>\n<p id=\"fs-id2552695\">Endoplasmic reticulum can exist in two forms: rough ER and smooth ER. These two types of ER perform some very different functions and can be found in very different amounts depending on the type of cell. Rough ER (RER) is so-called because its membrane is dotted with embedded granules\u2014organelles called ribosomes, giving the RER a bumpy appearance. A <strong>ribosome<\/strong> is an organelle that serves as the site of protein synthesis. It is composed of two ribosomal RNA subunits that wrap around mRNA to start the process of translation, followed by protein synthesis. Smooth ER (SER) lacks these ribosomes.<\/p>\n<p id=\"fs-id1858545\">One of the main functions of the smooth ER is in the synthesis of lipids. The smooth ER synthesizes phospholipids, the main component of biological membranes, as well as steroid hormones. For this reason, cells that produce large quantities of such hormones, such as those of the female ovaries and male testes, contain large amounts of smooth ER. In addition to lipid synthesis, the smooth ER also sequesters (i.e., stores) and regulates the concentration of cellular Ca<sup>2+<\/sup>, a function extremely important in cells of the nervous system where Ca<sup>2+<\/sup> is the trigger for neurotransmitter release. The smooth ER additionally metabolizes some carbohydrates and performs a detoxification role, breaking down certain toxins.<\/p>\n<p id=\"fs-id2581786\">In contrast with the smooth ER, the primary job of the rough ER is the synthesis and modification of proteins destined for the cell membrane or for export from the cell. For this protein synthesis, many ribosomes attach to the ER (giving it the studded appearance of rough ER). Typically, a protein is synthesized within the ribosome and released inside the channel of the rough ER, where sugars can be added to it (by a process called glycosylation) before it is transported within a <strong>vesicle<\/strong> to the next stage in the packaging and shipping process: the Golgi apparatus.<\/p>\n<\/section>\n<section id=\"fs-id2651407\">\n<h2>The Golgi Apparatus<\/h2>\n<p>The <strong>Golgi apparatus<\/strong> is responsible for sorting, modifying, and shipping off the products that come from the rough ER, much like a post-office. The Golgi apparatus looks like stacked flattened discs, almost like stacks of oddly shaped pancakes. Like the ER, these discs are membranous. The Golgi apparatus has two distinct sides, each with a different role. One side of the apparatus receives products in vesicles. These products are sorted through the apparatus, and then they are released from the opposite side after being repackaged into new vesicles. If the product is to be exported from the cell, the vesicle migrates to the cell surface and fuses to the cell membrane, and the cargo is secreted (<a class=\"autogenerated-content\" href=\"#fig-ch03_02_03\">Figure 3<\/a>).<\/p>\n<figure style=\"width: 550px\" class=\"wp-caption aligncenter\"><img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/pressbooks.bccampus.ca\/dcbiol11031109\/wp-content\/uploads\/sites\/149\/2017\/08\/0314_Golgi_Apparatus-3.jpg\" alt=\"This figure shows the structure of the Golgi apparatus. The diagram in the left panel shows the location and structure of the Golgi apparatus. The right panel shows a micrograph showing the folds of the Golgi in detail.\" width=\"550\" height=\"754\" \/><figcaption class=\"wp-caption-text\">Figure 3. Golgi Apparatus. (a) The Golgi apparatus manipulates products from the rough ER, and also produces new organelles called lysosomes. Proteins and other products of the ER are sent to the Golgi apparatus, which organizes, modifies, packages, and tags them. Some of these products are transported to other areas of the cell and some are exported from the cell through exocytosis. Enzymatic proteins are packaged as new lysosomes (or packaged and sent for fusion with existing lysosomes). (b) An electron micrograph of the Golgi apparatus.<\/figcaption><\/figure>\n<\/section>\n<section id=\"fs-id1661207\">\n<h2>Lysosomes<\/h2>\n<p id=\"fs-id2027468\">Some of the protein products packaged by the Golgi include digestive enzymes that are meant to remain inside the cell for use in breaking down certain materials. The enzyme-containing vesicles released by the Golgi may form new lysosomes, or fuse with existing, lysosomes. A <strong>lysosome<\/strong> is an organelle that contains enzymes that break down and digest unneeded cellular components, such as a damaged organelle. (A lysosome is similar to a wrecking crew that takes down old and unsound buildings in a neighborhood.) <strong>Autophagy<\/strong> (\u201cself-eating\u201d) is the process of a cell digesting its own structures. Lysosomes are also important for breaking down foreign material. For example, when certain immune defense cells (white blood cells) phagocytize bacteria, the bacterial cell is transported into a lysosome and digested by the enzymes inside. As one might imagine, such phagocytic defense cells contain large numbers of lysosomes.<\/p>\n<p id=\"fs-id2549673\">Under certain circumstances, lysosomes perform a more grand and dire function. In the case of damaged or unhealthy cells, lysosomes can be triggered to open up and release their digestive enzymes into the cytoplasm of the cell, killing the cell. This \u201cself-destruct\u201d mechanism is called <strong>autolysis<\/strong>, and makes the process of cell death controlled (a mechanism called \u201capoptosis\u201d).<\/p>\n<p>Watch this Khan Academy <a href=\"https:\/\/www.youtube.com\/watch?v=vC-cEWJxDRY\">video<\/a> to learn more about the endomembrane system<\/p>\n<\/section>\n<\/section>\n<section>\n<h1>Organelles for Energy Production<\/h1>\n<p id=\"fs-id1988147\">In addition to the jobs performed by the endomembrane system, the cell has many other important functions. Just as you must consume nutrients to provide yourself with energy, so must each of your cells take in nutrient molecules whose chemical energy can be harvested to power biochemical reactions.<\/p>\n<section id=\"fs-id1334972\">\n<h2 style=\"text-align: left\">Mitochondria<\/h2>\n<figure style=\"width: 520px\" class=\"wp-caption aligncenter\"><img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/pressbooks.bccampus.ca\/dcbiol11031109\/wp-content\/uploads\/sites\/149\/2017\/08\/0315_Mitochondrion_new-3.jpg\" alt=\"This figure shows the structure of a mitochondrion. The inner and outer membrane, the cristae and the intermembrane space are labeled. The right panel shows a micrograph with the structure of a mitochondrion in detail.\" width=\"520\" height=\"991\" \/><figcaption class=\"wp-caption-text\">Figure 4. Mitochondrion. The mitochondria are the energy-conversion factories of the cell. (a) A mitochondrion is composed of two separate lipid bilayer membranes. Along the inner membrane are various molecules that work together to produce ATP, the cell\u2019s major energy currency. (b) An electron micrograph of mitochondria. EM \u00d7 236,000. (Micrograph provided by the Regents of University of Michigan Medical School \u00a9 2012)<\/figcaption><\/figure>\n<p id=\"fs-id1692132\">A <strong>mitochondrion<\/strong> (plural = mitochondria) is a membranous, bean-shaped organelle that is the \u201cenergy transformer\u201d of the cell. Mitochondria consist of an outer lipid bilayer membrane as well as an additional inner lipid bilayer membrane (<a class=\"autogenerated-content\" href=\"#fig-ch03_02_04\">Figure 4<\/a>). The inner membrane is highly folded into winding structures with a great deal of surface area, called cristae. It is along this inner membrane that a series of proteins, enzymes, and other molecules perform the biochemical reactions of cellular respiration. These reactions convert energy stored in nutrient molecules (such as glucose) into adenosine triphosphate (ATP), which provides usable cellular energy to the cell. Cells use ATP constantly, and so the mitochondria are constantly at work. Oxygen molecules are required during cellular respiration, which is why you must constantly breathe it in. One of the organ systems in the body that uses huge amounts of ATP is the muscular system because ATP is required to sustain muscle contraction. As a result, muscle cells are packed full of mitochondria. Nerve cells also need large quantities of ATP to run their sodium-potassium pumps. Therefore, an individual neuron will be loaded with over a thousand mitochondria. On the other hand, a bone cell, which is not nearly as metabolically-active, might only have a couple hundred mitochondria.<\/p>\n<\/section>\n<\/section>\n","protected":false},"author":10,"menu_order":3,"template":"","meta":{"pb_show_title":"on","pb_short_title":"","pb_subtitle":"","pb_authors":[],"pb_section_license":""},"chapter-type":[],"contributor":[],"license":[],"class_list":["post-786","chapter","type-chapter","status-publish","hentry"],"part":763,"_links":{"self":[{"href":"https:\/\/pressbooks.bccampus.ca\/dcbiol11031109\/wp-json\/pressbooks\/v2\/chapters\/786","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/pressbooks.bccampus.ca\/dcbiol11031109\/wp-json\/pressbooks\/v2\/chapters"}],"about":[{"href":"https:\/\/pressbooks.bccampus.ca\/dcbiol11031109\/wp-json\/wp\/v2\/types\/chapter"}],"author":[{"embeddable":true,"href":"https:\/\/pressbooks.bccampus.ca\/dcbiol11031109\/wp-json\/wp\/v2\/users\/10"}],"version-history":[{"count":6,"href":"https:\/\/pressbooks.bccampus.ca\/dcbiol11031109\/wp-json\/pressbooks\/v2\/chapters\/786\/revisions"}],"predecessor-version":[{"id":1407,"href":"https:\/\/pressbooks.bccampus.ca\/dcbiol11031109\/wp-json\/pressbooks\/v2\/chapters\/786\/revisions\/1407"}],"part":[{"href":"https:\/\/pressbooks.bccampus.ca\/dcbiol11031109\/wp-json\/pressbooks\/v2\/parts\/763"}],"metadata":[{"href":"https:\/\/pressbooks.bccampus.ca\/dcbiol11031109\/wp-json\/pressbooks\/v2\/chapters\/786\/metadata\/"}],"wp:attachment":[{"href":"https:\/\/pressbooks.bccampus.ca\/dcbiol11031109\/wp-json\/wp\/v2\/media?parent=786"}],"wp:term":[{"taxonomy":"chapter-type","embeddable":true,"href":"https:\/\/pressbooks.bccampus.ca\/dcbiol11031109\/wp-json\/pressbooks\/v2\/chapter-type?post=786"},{"taxonomy":"contributor","embeddable":true,"href":"https:\/\/pressbooks.bccampus.ca\/dcbiol11031109\/wp-json\/wp\/v2\/contributor?post=786"},{"taxonomy":"license","embeddable":true,"href":"https:\/\/pressbooks.bccampus.ca\/dcbiol11031109\/wp-json\/wp\/v2\/license?post=786"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}