{"id":69,"date":"2015-04-03T17:27:08","date_gmt":"2015-04-03T17:27:08","guid":{"rendered":"https:\/\/courses.candelalearning.com\/biology2xmaster\/?post_type=chapter&#038;p=69"},"modified":"2015-07-06T19:03:20","modified_gmt":"2015-07-06T19:03:20","slug":"other-acellular-entities-prions-and-viroids","status":"publish","type":"chapter","link":"https:\/\/courses.lumenlearning.com\/suny-mcc-biology2\/chapter\/other-acellular-entities-prions-and-viroids\/","title":{"raw":"Other Acellular Entities: Prions and Viroids","rendered":"Other Acellular Entities: Prions and Viroids"},"content":{"raw":"<div class=\"bcc-box bcc-highlight\">\r\n<h3>Learning Objectives<\/h3>\r\nBy the end of this section, you will have completed the following objectives:\r\n<ul>\r\n\t<li>Describe prions and their basic properties<\/li>\r\n\t<li>Define viroids and their targets of infection<\/li>\r\n<\/ul>\r\n<\/div>\r\nPrions and viroids are <span data-type=\"term\">pathogens<\/span> (agents with the ability to cause disease) that have simpler structures than viruses but, in the case of prions, still can produce deadly diseases.\r\n<h2>Prions<\/h2>\r\n<b>Prions<\/b>, so-called because they are proteinaceous, are infectious particles\u2014smaller than viruses\u2014that contain no nucleic acids (neither DNA nor RNA). Historically, the idea of an infectious agent that did not use nucleic acids was considered impossible, but pioneering work by Nobel Prize-winning biologist Stanley Prusiner has convinced the majority of biologists that such agents do indeed exist.\r\n\r\nFatal neurodegenerative diseases, such as kuru in humans and bovine spongiform encephalopathy (BSE) in cattle (commonly known as \u201cmad cow disease\u201d) were shown to be transmitted by prions. The disease was spread by the consumption of meat, nervous tissue, or internal organs between members of the same species. Kuru, native to humans in Papua New Guinea, was spread from human to human via ritualistic cannibalism. BSE, originally detected in the United Kingdom, was spread between cattle by the practice of including cattle nervous tissue in feed for other cattle. Individuals with kuru and BSE show symptoms of loss of motor control and unusual behaviors, such as uncontrolled bursts of laughter with kuru, followed by death. Kuru was controlled by inducing the population to abandon its ritualistic cannibalism.\r\n\r\nOn the other hand, BSE was initially thought to only affect cattle. Cattle dying of the disease were shown to have developed lesions or \u201choles\u201d in the brain, causing the brain tissue to resemble a sponge. Later on in the outbreak, however, it was shown that a similar encephalopathy in humans known as variant Creutzfeldt-Jakob disease (CJD) could be acquired from eating beef from animals with BSE, sparking bans by various countries on the importation of British beef and causing considerable economic damage to the British beef industry (Figure 1). BSE still exists in various areas, and although a rare disease, individuals that acquire CJD are difficult to treat. The disease can be spread from human to human by blood, so many countries have banned blood donation from regions associated with BSE.\r\n\r\nThe cause of spongiform encephalopathies, such as kuru and BSE, is an infectious structural variant of a normal cellular protein called PrP (prion protein). It is this variant that constitutes the prion particle. PrP exists in two forms, <b>PrP<sup>c<\/sup><\/b>, the normal form of the protein, and <b>PrP<sup>sc<\/sup><\/b>, the infectious form. Once introduced into the body, the PrP<sup>sc <\/sup>contained within the prion binds to PrP<sup>c <\/sup>and converts it to PrP<sup>sc<\/sup>. This leads to an exponential increase of the PrP<sup>sc<\/sup> protein, which aggregates. PrP<sup>sc <\/sup>is folded abnormally, and the resulting conformation (shape) is directly responsible for the lesions seen in the brains of infected cattle. Thus, although not without some detractors among scientists, the prion seems likely to be an entirely new form of infectious agent, the first one found whose transmission is not reliant upon genes made of DNA or RNA.\r\n\r\n<figure>\r\n\r\n[caption id=\"\" align=\"aligncenter\" width=\"600\"]<img src=\"http:\/\/cnx.org\/resources\/beee144b545a08d48128e6729f2561a2\/Figure_21_04_01ab.jpg\" alt=\"Part a illustrates how normal prion protein (PRP) is converted into the disease-causing form (PRP). PRPsc may spontaneously form in brain tissue, may be introduced when a mutant form of the protein misfolds, or may introduced into the brain tissue by inoculation. The misfolded protein causes normal PRP already present in the brain to misfold. A chain reaction occurs, leading to a large amount of misfolded protein.\" width=\"600\" data-media-type=\"image\/jpg\" \/> Figure 1. (PrPsc) when it encounters this variant form of the protein. PrPsc may arise spontaneously in brain tissue, especially if a mutant form of the protein is present, or it may occur via the spread of misfolded prions consumed in food into brain tissue. (b) This prion-infected brain tissue, visualized using light microscopy, shows the vacuoles that give it a spongy texture, typical of transmissible spongiform encephalopathies. (credit b: modification of work by Dr. Al Jenny, USDA APHIS; scale-bar data from Matt Russell)[\/caption]\r\n\r\n<\/figure>\r\n<h2>Viroids<\/h2>\r\n<figure>\r\n\r\n[caption id=\"\" align=\"alignright\" width=\"350\"]<img src=\"http:\/\/cnx.org\/resources\/c9bf0dfce6a9210de89bebbe0e002448\/Figure_21_04_02.jpg\" alt=\"The photo shows shriveled, cracked potatoes.\" width=\"350\" data-media-type=\"image\/jpg\" \/> Figure 2. These potatoes have been infected by the potato spindle tuber viroid, which is typically spreads when infected knives cut healthy potatoes, which are then planted. (credit: Pamela Roberts, University of Florida Institute of Food and Agricultural Sciences, USDA ARS)[\/caption]\r\n\r\n<\/figure><b>Viroids<\/b> are plant pathogens: small, single-stranded, circular RNA particles that are much simpler than a virus. They do not have a capsid or outer envelope, but like viruses can reproduce only within a host cell. Viroids do not, however, manufacture any proteins, and they only produce a single, specific RNA molecule. Human diseases caused by viroids have yet to be identified.\r\n\r\nViroids are known to infect plants (Figure 2) and are responsible for crop failures and the loss of millions of dollars in agricultural revenue each year. Some of the plants they infect include potatoes, cucumbers, tomatoes, chrysanthemums, avocados, and coconut palms.\r\n<div class=\"bcc-box bcc-success\">\r\n<h3>Career Connection<\/h3>\r\n<h4>Virologist<\/h4>\r\n<figure>\r\n\r\n[caption id=\"\" align=\"alignright\" width=\"300\"]<img src=\"http:\/\/cnx.org\/resources\/80b8087d78fdd34d83852afe9d34efaf\/Figure_21_04_03.jpg\" alt=\"This photo shows a scientist in a field, measuring the length of an egg.\" width=\"300\" data-media-type=\"image\/jpg\" \/> Figure 3. This virologist is engaged in fieldwork, sampling eggs from this nest for avian influenza. (credit: Don Becker, USGS EROS, U.S. Fish and Wildlife Service)[\/caption]\r\n\r\n<\/figure>Virology is the study of viruses, and a virologist is an individual trained in this discipline. Training in virology can lead to many different career paths. Virologists are actively involved in academic research and teaching in colleges and medical schools. Some virologists treat patients or are involved in the generation and production of vaccines. They might participate in epidemiologic studies (Figure 3) or become science writers, to name just a few possible careers.\r\n\r\nIf you think you may be interested in a career in virology, find a mentor in the field. Many large medical centers have departments of virology, and smaller hospitals usually have virology labs within their microbiology departments. Volunteer in a virology lab for a semester or work in one over the summer. Discussing the profession and getting a first-hand look at the work will help you decide whether a career in virology is right for you. The American Society of Virology\u2019s <a href=\"http:\/\/www.asv.org\/\" target=\"_blank\">website<\/a> is a good resource for information regarding training and careers in virology.\r\n\r\n<\/div>\r\n<h2>Section Summary<\/h2>\r\nPrions are infectious agents that consist of protein, but no DNA or RNA, and seem to produce their deadly effects by duplicating their shapes and accumulating in tissues. They are thought to contribute to several progressive brain disorders, including mad cow disease and Creutzfeldt-Jakob disease. Viroids are single-stranded RNA pathogens that infect plants. Their presence can have a severe impact on the agriculture industry.\r\n<div class=\"bcc-box bcc-success\">\r\n<h3>Glossary<\/h3>\r\n<div id=\"fs-idp90498592\" data-type=\"definition\">\r\n<div id=\"fs-idp193016160\" data-type=\"definition\">\r\n\r\n<strong><span data-type=\"term\">pathogen:\u00a0<\/span><\/strong>agent with the ability to cause disease\r\n\r\n<\/div>\r\n<div id=\"fs-idm7321664\" data-type=\"definition\">\r\n\r\n<strong><span data-type=\"term\">prion:\u00a0<\/span><\/strong>infectious particle that consists of proteins that replicate without DNA or RNA\r\n\r\n<\/div>\r\n<div id=\"fs-idp20683008\" data-type=\"definition\">\r\n\r\n<strong><span data-type=\"term\">PrP<sup>c<\/sup><\/span>:<\/strong> normal prion protein\r\n\r\n<\/div>\r\n<div id=\"fs-idm81436928\" data-type=\"definition\">\r\n\r\n<strong><span data-type=\"term\">PrP<sup>sc<\/sup><\/span>:<\/strong> infectious form of a prion protein\r\n\r\n<\/div>\r\n<div id=\"fs-idp148270624\" data-type=\"definition\">\r\n\r\n<strong><span data-type=\"term\">viroid:\u00a0<\/span><\/strong>plant pathogen that produces only a single, specific RNA\r\n\r\n<\/div>\r\n<\/div>\r\n<\/div>","rendered":"<div class=\"bcc-box bcc-highlight\">\n<h3>Learning Objectives<\/h3>\n<p>By the end of this section, you will have completed the following objectives:<\/p>\n<ul>\n<li>Describe prions and their basic properties<\/li>\n<li>Define viroids and their targets of infection<\/li>\n<\/ul>\n<\/div>\n<p>Prions and viroids are <span data-type=\"term\">pathogens<\/span> (agents with the ability to cause disease) that have simpler structures than viruses but, in the case of prions, still can produce deadly diseases.<\/p>\n<h2>Prions<\/h2>\n<p><b>Prions<\/b>, so-called because they are proteinaceous, are infectious particles\u2014smaller than viruses\u2014that contain no nucleic acids (neither DNA nor RNA). Historically, the idea of an infectious agent that did not use nucleic acids was considered impossible, but pioneering work by Nobel Prize-winning biologist Stanley Prusiner has convinced the majority of biologists that such agents do indeed exist.<\/p>\n<p>Fatal neurodegenerative diseases, such as kuru in humans and bovine spongiform encephalopathy (BSE) in cattle (commonly known as \u201cmad cow disease\u201d) were shown to be transmitted by prions. The disease was spread by the consumption of meat, nervous tissue, or internal organs between members of the same species. Kuru, native to humans in Papua New Guinea, was spread from human to human via ritualistic cannibalism. BSE, originally detected in the United Kingdom, was spread between cattle by the practice of including cattle nervous tissue in feed for other cattle. Individuals with kuru and BSE show symptoms of loss of motor control and unusual behaviors, such as uncontrolled bursts of laughter with kuru, followed by death. Kuru was controlled by inducing the population to abandon its ritualistic cannibalism.<\/p>\n<p>On the other hand, BSE was initially thought to only affect cattle. Cattle dying of the disease were shown to have developed lesions or \u201choles\u201d in the brain, causing the brain tissue to resemble a sponge. Later on in the outbreak, however, it was shown that a similar encephalopathy in humans known as variant Creutzfeldt-Jakob disease (CJD) could be acquired from eating beef from animals with BSE, sparking bans by various countries on the importation of British beef and causing considerable economic damage to the British beef industry (Figure 1). BSE still exists in various areas, and although a rare disease, individuals that acquire CJD are difficult to treat. The disease can be spread from human to human by blood, so many countries have banned blood donation from regions associated with BSE.<\/p>\n<p>The cause of spongiform encephalopathies, such as kuru and BSE, is an infectious structural variant of a normal cellular protein called PrP (prion protein). It is this variant that constitutes the prion particle. PrP exists in two forms, <b>PrP<sup>c<\/sup><\/b>, the normal form of the protein, and <b>PrP<sup>sc<\/sup><\/b>, the infectious form. Once introduced into the body, the PrP<sup>sc <\/sup>contained within the prion binds to PrP<sup>c <\/sup>and converts it to PrP<sup>sc<\/sup>. This leads to an exponential increase of the PrP<sup>sc<\/sup> protein, which aggregates. PrP<sup>sc <\/sup>is folded abnormally, and the resulting conformation (shape) is directly responsible for the lesions seen in the brains of infected cattle. Thus, although not without some detractors among scientists, the prion seems likely to be an entirely new form of infectious agent, the first one found whose transmission is not reliant upon genes made of DNA or RNA.<\/p>\n<figure>\n<div style=\"width: 610px\" class=\"wp-caption aligncenter\"><img decoding=\"async\" src=\"http:\/\/cnx.org\/resources\/beee144b545a08d48128e6729f2561a2\/Figure_21_04_01ab.jpg\" alt=\"Part a illustrates how normal prion protein (PRP) is converted into the disease-causing form (PRP). PRPsc may spontaneously form in brain tissue, may be introduced when a mutant form of the protein misfolds, or may introduced into the brain tissue by inoculation. The misfolded protein causes normal PRP already present in the brain to misfold. A chain reaction occurs, leading to a large amount of misfolded protein.\" width=\"600\" data-media-type=\"image\/jpg\" \/><\/p>\n<p class=\"wp-caption-text\">Figure 1. (PrPsc) when it encounters this variant form of the protein. PrPsc may arise spontaneously in brain tissue, especially if a mutant form of the protein is present, or it may occur via the spread of misfolded prions consumed in food into brain tissue. (b) This prion-infected brain tissue, visualized using light microscopy, shows the vacuoles that give it a spongy texture, typical of transmissible spongiform encephalopathies. (credit b: modification of work by Dr. Al Jenny, USDA APHIS; scale-bar data from Matt Russell)<\/p>\n<\/div>\n<\/figure>\n<h2>Viroids<\/h2>\n<figure>\n<div style=\"width: 360px\" class=\"wp-caption alignright\"><img decoding=\"async\" src=\"http:\/\/cnx.org\/resources\/c9bf0dfce6a9210de89bebbe0e002448\/Figure_21_04_02.jpg\" alt=\"The photo shows shriveled, cracked potatoes.\" width=\"350\" data-media-type=\"image\/jpg\" \/><\/p>\n<p class=\"wp-caption-text\">Figure 2. These potatoes have been infected by the potato spindle tuber viroid, which is typically spreads when infected knives cut healthy potatoes, which are then planted. (credit: Pamela Roberts, University of Florida Institute of Food and Agricultural Sciences, USDA ARS)<\/p>\n<\/div>\n<\/figure>\n<p><b>Viroids<\/b> are plant pathogens: small, single-stranded, circular RNA particles that are much simpler than a virus. They do not have a capsid or outer envelope, but like viruses can reproduce only within a host cell. Viroids do not, however, manufacture any proteins, and they only produce a single, specific RNA molecule. Human diseases caused by viroids have yet to be identified.<\/p>\n<p>Viroids are known to infect plants (Figure 2) and are responsible for crop failures and the loss of millions of dollars in agricultural revenue each year. Some of the plants they infect include potatoes, cucumbers, tomatoes, chrysanthemums, avocados, and coconut palms.<\/p>\n<div class=\"bcc-box bcc-success\">\n<h3>Career Connection<\/h3>\n<h4>Virologist<\/h4>\n<figure>\n<div style=\"width: 310px\" class=\"wp-caption alignright\"><img decoding=\"async\" src=\"http:\/\/cnx.org\/resources\/80b8087d78fdd34d83852afe9d34efaf\/Figure_21_04_03.jpg\" alt=\"This photo shows a scientist in a field, measuring the length of an egg.\" width=\"300\" data-media-type=\"image\/jpg\" \/><\/p>\n<p class=\"wp-caption-text\">Figure 3. This virologist is engaged in fieldwork, sampling eggs from this nest for avian influenza. (credit: Don Becker, USGS EROS, U.S. Fish and Wildlife Service)<\/p>\n<\/div>\n<\/figure>\n<p>Virology is the study of viruses, and a virologist is an individual trained in this discipline. Training in virology can lead to many different career paths. Virologists are actively involved in academic research and teaching in colleges and medical schools. Some virologists treat patients or are involved in the generation and production of vaccines. They might participate in epidemiologic studies (Figure 3) or become science writers, to name just a few possible careers.<\/p>\n<p>If you think you may be interested in a career in virology, find a mentor in the field. Many large medical centers have departments of virology, and smaller hospitals usually have virology labs within their microbiology departments. Volunteer in a virology lab for a semester or work in one over the summer. Discussing the profession and getting a first-hand look at the work will help you decide whether a career in virology is right for you. The American Society of Virology\u2019s <a href=\"http:\/\/www.asv.org\/\" target=\"_blank\">website<\/a> is a good resource for information regarding training and careers in virology.<\/p>\n<\/div>\n<h2>Section Summary<\/h2>\n<p>Prions are infectious agents that consist of protein, but no DNA or RNA, and seem to produce their deadly effects by duplicating their shapes and accumulating in tissues. They are thought to contribute to several progressive brain disorders, including mad cow disease and Creutzfeldt-Jakob disease. Viroids are single-stranded RNA pathogens that infect plants. Their presence can have a severe impact on the agriculture industry.<\/p>\n<div class=\"bcc-box bcc-success\">\n<h3>Glossary<\/h3>\n<div id=\"fs-idp90498592\" data-type=\"definition\">\n<div id=\"fs-idp193016160\" data-type=\"definition\">\n<p><strong><span data-type=\"term\">pathogen:\u00a0<\/span><\/strong>agent with the ability to cause disease<\/p>\n<\/div>\n<div id=\"fs-idm7321664\" data-type=\"definition\">\n<p><strong><span data-type=\"term\">prion:\u00a0<\/span><\/strong>infectious particle that consists of proteins that replicate without DNA or RNA<\/p>\n<\/div>\n<div id=\"fs-idp20683008\" data-type=\"definition\">\n<p><strong><span data-type=\"term\">PrP<sup>c<\/sup><\/span>:<\/strong> normal prion protein<\/p>\n<\/div>\n<div id=\"fs-idm81436928\" data-type=\"definition\">\n<p><strong><span data-type=\"term\">PrP<sup>sc<\/sup><\/span>:<\/strong> infectious form of a prion protein<\/p>\n<\/div>\n<div id=\"fs-idp148270624\" data-type=\"definition\">\n<p><strong><span data-type=\"term\">viroid:\u00a0<\/span><\/strong>plant pathogen that produces only a single, specific RNA<\/p>\n<\/div>\n<\/div>\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-69\">\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. <strong>Authored by<\/strong>: OpenStax. <strong>Provided by<\/strong>: OpenStax College. <strong>Located at<\/strong>: <a target=\"_blank\" href=\"http:\/\/cnx.org\/contents\/185cbf87-c72e-48f5-b51e-f14f21b5eabd@9.44:1\/Biology\">http:\/\/cnx.org\/contents\/185cbf87-c72e-48f5-b51e-f14f21b5eabd@9.44:1\/Biology<\/a>. <strong>License<\/strong>: <em><a target=\"_blank\" rel=\"license\" href=\"https:\/\/creativecommons.org\/licenses\/by\/4.0\/\">CC BY: Attribution<\/a><\/em><\/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":78,"menu_order":5,"template":"","meta":{"_candela_citation":"[{\"type\":\"cc\",\"description\":\"Biology\",\"author\":\"OpenStax\",\"organization\":\"OpenStax College\",\"url\":\"http:\/\/cnx.org\/contents\/185cbf87-c72e-48f5-b51e-f14f21b5eabd@9.44:1\/Biology\",\"project\":\"\",\"license\":\"cc-by\",\"license_terms\":\"\"}]","CANDELA_OUTCOMES_GUID":"","pb_show_title":"on","pb_short_title":"","pb_subtitle":"","pb_authors":[],"pb_section_license":""},"chapter-type":[],"contributor":[],"license":[],"class_list":["post-69","chapter","type-chapter","status-publish","hentry"],"part":17,"_links":{"self":[{"href":"https:\/\/courses.lumenlearning.com\/suny-mcc-biology2\/wp-json\/pressbooks\/v2\/chapters\/69","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/courses.lumenlearning.com\/suny-mcc-biology2\/wp-json\/pressbooks\/v2\/chapters"}],"about":[{"href":"https:\/\/courses.lumenlearning.com\/suny-mcc-biology2\/wp-json\/wp\/v2\/types\/chapter"}],"author":[{"embeddable":true,"href":"https:\/\/courses.lumenlearning.com\/suny-mcc-biology2\/wp-json\/wp\/v2\/users\/78"}],"version-history":[{"count":5,"href":"https:\/\/courses.lumenlearning.com\/suny-mcc-biology2\/wp-json\/pressbooks\/v2\/chapters\/69\/revisions"}],"predecessor-version":[{"id":715,"href":"https:\/\/courses.lumenlearning.com\/suny-mcc-biology2\/wp-json\/pressbooks\/v2\/chapters\/69\/revisions\/715"}],"part":[{"href":"https:\/\/courses.lumenlearning.com\/suny-mcc-biology2\/wp-json\/pressbooks\/v2\/parts\/17"}],"metadata":[{"href":"https:\/\/courses.lumenlearning.com\/suny-mcc-biology2\/wp-json\/pressbooks\/v2\/chapters\/69\/metadata\/"}],"wp:attachment":[{"href":"https:\/\/courses.lumenlearning.com\/suny-mcc-biology2\/wp-json\/wp\/v2\/media?parent=69"}],"wp:term":[{"taxonomy":"chapter-type","embeddable":true,"href":"https:\/\/courses.lumenlearning.com\/suny-mcc-biology2\/wp-json\/pressbooks\/v2\/chapter-type?post=69"},{"taxonomy":"contributor","embeddable":true,"href":"https:\/\/courses.lumenlearning.com\/suny-mcc-biology2\/wp-json\/wp\/v2\/contributor?post=69"},{"taxonomy":"license","embeddable":true,"href":"https:\/\/courses.lumenlearning.com\/suny-mcc-biology2\/wp-json\/wp\/v2\/license?post=69"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}