{"id":4169,"date":"2017-03-27T23:05:22","date_gmt":"2017-03-27T23:05:22","guid":{"rendered":"https:\/\/courses.lumenlearning.com\/wm-biology2\/?post_type=chapter&#038;p=4169"},"modified":"2024-04-26T02:36:45","modified_gmt":"2024-04-26T02:36:45","slug":"nitrogenous-wastes","status":"publish","type":"chapter","link":"https:\/\/courses.lumenlearning.com\/wm-biology2\/chapter\/nitrogenous-wastes\/","title":{"raw":"Nitrogenous Wastes","rendered":"Nitrogenous Wastes"},"content":{"raw":"<div class=\"textbox learning-objectives\">\r\n<h3>Learning Outcomes<\/h3>\r\n<ul>\r\n \t<li>Identify common wastes and waste systems<\/li>\r\n<\/ul>\r\n<\/div>\r\nOf the four major macromolecules in biological systems, both proteins and nucleic acids contain nitrogen. During the catabolism, or breakdown, of nitrogen-containing macromolecules, carbon, hydrogen, and oxygen are extracted and stored in the form of carbohydrates and fats. Excess nitrogen is excreted from the body. Nitrogenous wastes tend to form toxic <b>ammonia<\/b>, which raises the pH of body fluids. The formation of ammonia itself requires energy in the form of ATP and large quantities of water to dilute it out of a biological system. Animals that live in aquatic environments tend to release ammonia into the water. Animals that excrete ammonia are said to be <b>ammonotelic<\/b>. Terrestrial organisms have evolved other mechanisms to excrete nitrogenous wastes. The animals must detoxify ammonia by converting it into a relatively nontoxic form such as urea or uric acid. Mammals, including humans, produce urea, whereas reptiles and many terrestrial invertebrates produce uric acid. Animals that secrete urea as the primary nitrogenous waste material are called <b>ureotelic<\/b> animals.\r\n<h2>Terrestrial Animals: The Urea Cycle<\/h2>\r\nThe <b>urea cycle<\/b> is the primary mechanism by which mammals convert ammonia to urea. Urea is made in the liver and excreted in urine. The overall chemical reaction by which ammonia is converted to urea is 2 NH<sub>3<\/sub> (ammonia) + CO<sub>2<\/sub> + 3 ATP + H<sub>2<\/sub>O \u2192 H<sub>2<\/sub>N-CO-NH<sub>2<\/sub> (urea) + 2 ADP + 4 P<sub>i<\/sub> + AMP.\r\n\r\nThe urea cycle utilizes five intermediate steps, catalyzed by five different enzymes, to convert ammonia to urea, as shown in Figure 1. The amino acid L-ornithine gets converted into different intermediates before being regenerated at the end of the urea cycle. Hence, the urea cycle is also referred to as the ornithine cycle. The enzyme ornithine transcarbamylase catalyzes a key step in the urea cycle and its deficiency can lead to accumulation of toxic levels of ammonia in the body. The first two reactions occur in the mitochondria and the last three reactions occur in the cytosol. Urea concentration in the blood, called <b>blood urea nitrogen<\/b> or BUN, is used as an indicator of kidney function.\r\n\r\n[caption id=\"attachment_2963\" align=\"aligncenter\" width=\"750\"]<img class=\"wp-image-2963\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/1223\/2017\/02\/09001041\/Figure_41_04_01-920x1024.jpg\" alt=\" The urea cycle begins in the mitochondrion, where bicarbonate (HCO3) is combined with ammonia (NH3) to make carbamoyl phosphate. Two ATP are used in the process. Ornithine transcarbamylase adds the carbamoyl phosphate to a five-carbon amino acid called ornithine to make L-citrulline. L-citrulline leaves the mitochondrion, and an enzyme called arginosuccinate synthetase adds a four-carbon amino acid called L-aspartate to it to make arginosuccinate. In the process, one ATP is converted to AMP and PPi. Arginosuccinate lyase removes a four-carbon fumarate molecule from the arginosuccinate, forming the six-carbon amino acid L-arginine. Arginase-1 removes a urea molecule from the L-arginine, forming ornithine in the process. Urea has a single carbon double-bonded to an oxygen and single-bonded to two ammonia groups. Ornithine enters the mitochondrion, completing the cycle.\" width=\"750\" height=\"835\" \/> Figure 1.\u00a0The urea cycle converts ammonia to urea.[\/caption]\r\n\r\n<div class=\"textbox key-takeaways\">\r\n<h3>Excretion of Nitrogenous Waste<\/h3>\r\nThe theory of evolution proposes that life started in an aquatic environment. It is not surprising to see that biochemical pathways like the urea cycle evolved to adapt to a changing environment when terrestrial life forms evolved. Arid conditions probably led to the evolution of the uric acid pathway as a means of conserving water.\r\n\r\n<\/div>\r\n<h2>Birds and Reptiles: Uric Acid<\/h2>\r\nBirds, reptiles, and most terrestrial arthropods convert toxic ammonia to <b>uric acid<\/b> or the closely related compound guanine (guano) instead of urea. Mammals also form some uric acid during breakdown of nucleic acids. Uric acid is a compound similar to purines found in nucleic acids. It is water insoluble and tends to form a white paste or powder; it is excreted by birds, insects, and reptiles. Conversion of ammonia to uric acid requires more energy and is much more complex than conversion of ammonia to urea Figure 2.\r\n\r\n[caption id=\"attachment_2964\" align=\"aligncenter\" width=\"1024\"]<img class=\"size-large wp-image-2964\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/1223\/2017\/02\/09001119\/Figure_41_04_02abc-1024x256.jpg\" alt=\"Part A shows a photo of a freshwater fish and states that many invertebrates and aquatic species excrete ammonia. The chemical structure of ammonia is NH3. Part B shows a photo of a wood rat and states that mammals, many adult amphibians, and some marine species excrete urea. The chemical structure of urea is shown. Urea has two NH2 groups attached to a central carbon. An oxygen is also double-bonded to this central carbon. Part C shows a photo of a pigeon and states that insects, land snails, birds, and many reptiles excrete uric acid. The chemical structure of uric acid is shown. Uric acid has a six-membered carbon ring attached to a five-membered ring. Each ring has two NH groups embedded in it. An oxygen is double-bonded to each ring.\" width=\"1024\" height=\"256\" \/> Figure 2.\u00a0Nitrogenous waste is excreted in different forms by different species. These include (a) ammonia, (b) urea, and (c) uric acid. (credit a: modification of work by Eric Engbretson, USFWS; credit b: modification of work by B. \"Moose\" Peterson, USFWS; credit c: modification of work by Dave Menke, USFWS)[\/caption]\r\n\r\n<div class=\"textbox shaded\">\r\n<h4 class=\"os-subtitle\" data-type=\"title\"><span class=\"os-subtitle-label\">Gout<\/span><\/h4>\r\n<p id=\"fs-idp722544\">Mammals use uric acid crystals as an\u00a0<span id=\"term2073\" data-type=\"term\">antioxidant<\/span>\u00a0in their cells. However, too much uric acid tends to form kidney stones and may also cause a painful condition called gout, where uric acid crystals accumulate in the joints, as illustrated in\u00a0Figure 3. Food choices that reduce the amount of nitrogenous bases in the diet help reduce the risk of gout. For example, tea, coffee, and chocolate have purine-like compounds, called xanthines, and should be avoided by people with gout and kidney stones.<\/p>\r\n\r\n\r\n[caption id=\"\" align=\"aligncenter\" width=\"350\"]<img id=\"7\" src=\"https:\/\/openstax.org\/resources\/e6adfc147348c0edeb92c858021729a557a92845\" alt=\"Photo shows a person's feet. One foot is swollen and red, while the other appears normal.\" width=\"350\" height=\"344\" data-media-type=\"image\/jpg\" \/> Figure 3. Gout causes the inflammation visible in this person\u2019s left big toe joint. (credit: \"Gonzosft\"\/Wikimedia Commons)[\/caption]\r\n\r\n<\/div>\r\n<div class=\"textbox tryit\">\r\n<h3>Try It<\/h3>\r\nhttps:\/\/assess.lumenlearning.com\/practice\/c17d546e-3712-4eed-96a9-de6be33ec000\r\n<\/div>","rendered":"<div class=\"textbox learning-objectives\">\n<h3>Learning Outcomes<\/h3>\n<ul>\n<li>Identify common wastes and waste systems<\/li>\n<\/ul>\n<\/div>\n<p>Of the four major macromolecules in biological systems, both proteins and nucleic acids contain nitrogen. During the catabolism, or breakdown, of nitrogen-containing macromolecules, carbon, hydrogen, and oxygen are extracted and stored in the form of carbohydrates and fats. Excess nitrogen is excreted from the body. Nitrogenous wastes tend to form toxic <b>ammonia<\/b>, which raises the pH of body fluids. The formation of ammonia itself requires energy in the form of ATP and large quantities of water to dilute it out of a biological system. Animals that live in aquatic environments tend to release ammonia into the water. Animals that excrete ammonia are said to be <b>ammonotelic<\/b>. Terrestrial organisms have evolved other mechanisms to excrete nitrogenous wastes. The animals must detoxify ammonia by converting it into a relatively nontoxic form such as urea or uric acid. Mammals, including humans, produce urea, whereas reptiles and many terrestrial invertebrates produce uric acid. Animals that secrete urea as the primary nitrogenous waste material are called <b>ureotelic<\/b> animals.<\/p>\n<h2>Terrestrial Animals: The Urea Cycle<\/h2>\n<p>The <b>urea cycle<\/b> is the primary mechanism by which mammals convert ammonia to urea. Urea is made in the liver and excreted in urine. The overall chemical reaction by which ammonia is converted to urea is 2 NH<sub>3<\/sub> (ammonia) + CO<sub>2<\/sub> + 3 ATP + H<sub>2<\/sub>O \u2192 H<sub>2<\/sub>N-CO-NH<sub>2<\/sub> (urea) + 2 ADP + 4 P<sub>i<\/sub> + AMP.<\/p>\n<p>The urea cycle utilizes five intermediate steps, catalyzed by five different enzymes, to convert ammonia to urea, as shown in Figure 1. The amino acid L-ornithine gets converted into different intermediates before being regenerated at the end of the urea cycle. Hence, the urea cycle is also referred to as the ornithine cycle. The enzyme ornithine transcarbamylase catalyzes a key step in the urea cycle and its deficiency can lead to accumulation of toxic levels of ammonia in the body. The first two reactions occur in the mitochondria and the last three reactions occur in the cytosol. Urea concentration in the blood, called <b>blood urea nitrogen<\/b> or BUN, is used as an indicator of kidney function.<\/p>\n<div id=\"attachment_2963\" style=\"width: 760px\" class=\"wp-caption aligncenter\"><img loading=\"lazy\" decoding=\"async\" aria-describedby=\"caption-attachment-2963\" class=\"wp-image-2963\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/1223\/2017\/02\/09001041\/Figure_41_04_01-920x1024.jpg\" alt=\"The urea cycle begins in the mitochondrion, where bicarbonate (HCO3) is combined with ammonia (NH3) to make carbamoyl phosphate. Two ATP are used in the process. Ornithine transcarbamylase adds the carbamoyl phosphate to a five-carbon amino acid called ornithine to make L-citrulline. L-citrulline leaves the mitochondrion, and an enzyme called arginosuccinate synthetase adds a four-carbon amino acid called L-aspartate to it to make arginosuccinate. In the process, one ATP is converted to AMP and PPi. Arginosuccinate lyase removes a four-carbon fumarate molecule from the arginosuccinate, forming the six-carbon amino acid L-arginine. Arginase-1 removes a urea molecule from the L-arginine, forming ornithine in the process. Urea has a single carbon double-bonded to an oxygen and single-bonded to two ammonia groups. Ornithine enters the mitochondrion, completing the cycle.\" width=\"750\" height=\"835\" \/><\/p>\n<p id=\"caption-attachment-2963\" class=\"wp-caption-text\">Figure 1.\u00a0The urea cycle converts ammonia to urea.<\/p>\n<\/div>\n<div class=\"textbox key-takeaways\">\n<h3>Excretion of Nitrogenous Waste<\/h3>\n<p>The theory of evolution proposes that life started in an aquatic environment. It is not surprising to see that biochemical pathways like the urea cycle evolved to adapt to a changing environment when terrestrial life forms evolved. Arid conditions probably led to the evolution of the uric acid pathway as a means of conserving water.<\/p>\n<\/div>\n<h2>Birds and Reptiles: Uric Acid<\/h2>\n<p>Birds, reptiles, and most terrestrial arthropods convert toxic ammonia to <b>uric acid<\/b> or the closely related compound guanine (guano) instead of urea. Mammals also form some uric acid during breakdown of nucleic acids. Uric acid is a compound similar to purines found in nucleic acids. It is water insoluble and tends to form a white paste or powder; it is excreted by birds, insects, and reptiles. Conversion of ammonia to uric acid requires more energy and is much more complex than conversion of ammonia to urea Figure 2.<\/p>\n<div id=\"attachment_2964\" style=\"width: 1034px\" class=\"wp-caption aligncenter\"><img loading=\"lazy\" decoding=\"async\" aria-describedby=\"caption-attachment-2964\" class=\"size-large wp-image-2964\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/1223\/2017\/02\/09001119\/Figure_41_04_02abc-1024x256.jpg\" alt=\"Part A shows a photo of a freshwater fish and states that many invertebrates and aquatic species excrete ammonia. The chemical structure of ammonia is NH3. Part B shows a photo of a wood rat and states that mammals, many adult amphibians, and some marine species excrete urea. The chemical structure of urea is shown. Urea has two NH2 groups attached to a central carbon. An oxygen is also double-bonded to this central carbon. Part C shows a photo of a pigeon and states that insects, land snails, birds, and many reptiles excrete uric acid. The chemical structure of uric acid is shown. Uric acid has a six-membered carbon ring attached to a five-membered ring. Each ring has two NH groups embedded in it. An oxygen is double-bonded to each ring.\" width=\"1024\" height=\"256\" \/><\/p>\n<p id=\"caption-attachment-2964\" class=\"wp-caption-text\">Figure 2.\u00a0Nitrogenous waste is excreted in different forms by different species. These include (a) ammonia, (b) urea, and (c) uric acid. (credit a: modification of work by Eric Engbretson, USFWS; credit b: modification of work by B. &#8220;Moose&#8221; Peterson, USFWS; credit c: modification of work by Dave Menke, USFWS)<\/p>\n<\/div>\n<div class=\"textbox shaded\">\n<h4 class=\"os-subtitle\" data-type=\"title\"><span class=\"os-subtitle-label\">Gout<\/span><\/h4>\n<p id=\"fs-idp722544\">Mammals use uric acid crystals as an\u00a0<span id=\"term2073\" data-type=\"term\">antioxidant<\/span>\u00a0in their cells. However, too much uric acid tends to form kidney stones and may also cause a painful condition called gout, where uric acid crystals accumulate in the joints, as illustrated in\u00a0Figure 3. Food choices that reduce the amount of nitrogenous bases in the diet help reduce the risk of gout. For example, tea, coffee, and chocolate have purine-like compounds, called xanthines, and should be avoided by people with gout and kidney stones.<\/p>\n<div style=\"width: 360px\" class=\"wp-caption aligncenter\"><img loading=\"lazy\" decoding=\"async\" id=\"7\" src=\"https:\/\/openstax.org\/resources\/e6adfc147348c0edeb92c858021729a557a92845\" alt=\"Photo shows a person's feet. One foot is swollen and red, while the other appears normal.\" width=\"350\" height=\"344\" data-media-type=\"image\/jpg\" \/><\/p>\n<p class=\"wp-caption-text\">Figure 3. Gout causes the inflammation visible in this person\u2019s left big toe joint. (credit: &#8220;Gonzosft&#8221;\/Wikimedia Commons)<\/p>\n<\/div>\n<\/div>\n<div class=\"textbox tryit\">\n<h3>Try It<\/h3>\n<p>\t<iframe id=\"assessment_practice_c17d546e-3712-4eed-96a9-de6be33ec000\" class=\"resizable\" src=\"https:\/\/assess.lumenlearning.com\/practice\/c17d546e-3712-4eed-96a9-de6be33ec000?iframe_resize_id=assessment_practice_id_c17d546e-3712-4eed-96a9-de6be33ec000\" frameborder=\"0\" style=\"border:none;width:100%;height:100%;min-height:300px;\"><br \/>\n\t<\/iframe>\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-4169\">\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=\"http:\/\/cnx.org\/contents\/185cbf87-c72e-48f5-b51e-f14f21b5eabd@10.8\">http:\/\/cnx.org\/contents\/185cbf87-c72e-48f5-b51e-f14f21b5eabd@10.8<\/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>: Access for free at https:\/\/openstax.org\/books\/biology-2e\/pages\/1-introduction<\/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":17,"menu_order":12,"template":"","meta":{"_candela_citation":"[{\"type\":\"cc\",\"description\":\"Biology 2e\",\"author\":\"\",\"organization\":\"OpenStax\",\"url\":\"http:\/\/cnx.org\/contents\/185cbf87-c72e-48f5-b51e-f14f21b5eabd@10.8\",\"project\":\"\",\"license\":\"cc-by\",\"license_terms\":\"Access for free at https:\/\/openstax.org\/books\/biology-2e\/pages\/1-introduction\"}]","CANDELA_OUTCOMES_GUID":"034587b8-8986-4d39-95c9-164c8f30a8b5, b23b7b46-2e1f-4c17-893c-288dd021082c","pb_show_title":"on","pb_short_title":"","pb_subtitle":"","pb_authors":[],"pb_section_license":""},"chapter-type":[],"contributor":[],"license":[],"class_list":["post-4169","chapter","type-chapter","status-publish","hentry"],"part":3795,"_links":{"self":[{"href":"https:\/\/courses.lumenlearning.com\/wm-biology2\/wp-json\/pressbooks\/v2\/chapters\/4169","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/courses.lumenlearning.com\/wm-biology2\/wp-json\/pressbooks\/v2\/chapters"}],"about":[{"href":"https:\/\/courses.lumenlearning.com\/wm-biology2\/wp-json\/wp\/v2\/types\/chapter"}],"author":[{"embeddable":true,"href":"https:\/\/courses.lumenlearning.com\/wm-biology2\/wp-json\/wp\/v2\/users\/17"}],"version-history":[{"count":8,"href":"https:\/\/courses.lumenlearning.com\/wm-biology2\/wp-json\/pressbooks\/v2\/chapters\/4169\/revisions"}],"predecessor-version":[{"id":8682,"href":"https:\/\/courses.lumenlearning.com\/wm-biology2\/wp-json\/pressbooks\/v2\/chapters\/4169\/revisions\/8682"}],"part":[{"href":"https:\/\/courses.lumenlearning.com\/wm-biology2\/wp-json\/pressbooks\/v2\/parts\/3795"}],"metadata":[{"href":"https:\/\/courses.lumenlearning.com\/wm-biology2\/wp-json\/pressbooks\/v2\/chapters\/4169\/metadata\/"}],"wp:attachment":[{"href":"https:\/\/courses.lumenlearning.com\/wm-biology2\/wp-json\/wp\/v2\/media?parent=4169"}],"wp:term":[{"taxonomy":"chapter-type","embeddable":true,"href":"https:\/\/courses.lumenlearning.com\/wm-biology2\/wp-json\/pressbooks\/v2\/chapter-type?post=4169"},{"taxonomy":"contributor","embeddable":true,"href":"https:\/\/courses.lumenlearning.com\/wm-biology2\/wp-json\/wp\/v2\/contributor?post=4169"},{"taxonomy":"license","embeddable":true,"href":"https:\/\/courses.lumenlearning.com\/wm-biology2\/wp-json\/wp\/v2\/license?post=4169"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}