{"id":2532,"date":"2016-06-02T17:32:09","date_gmt":"2016-06-02T17:32:09","guid":{"rendered":"https:\/\/courses.lumenlearning.com\/biologyxwaymakerxmaster\/?post_type=chapter&#038;p=2532"},"modified":"2024-04-29T16:26:10","modified_gmt":"2024-04-29T16:26:10","slug":"reading-telomeres","status":"publish","type":"chapter","link":"https:\/\/courses.lumenlearning.com\/wm-biology1\/chapter\/reading-telomeres\/","title":{"raw":"Telomeres","rendered":"Telomeres"},"content":{"raw":"<div class=\"textbox learning-objectives\">\r\n<h3>Learning Outcomes<\/h3>\r\n<ul>\r\n \t<li>Understand the basic role of telomeres in protecting DNA from replication errors<\/li>\r\n<\/ul>\r\n<\/div>\r\nAs you've learned, the enzyme DNA pol can add nucleotides only in the 5\u2032 to 3\u2032 direction. In the leading strand, synthesis continues until the end of the chromosome is reached. On the lagging strand, DNA is synthesized in short stretches, each of which is initiated by a separate primer. When the replication fork reaches the end of the linear chromosome, there is no place for a primer to be made for the DNA fragment to be copied at the end of the chromosome. These ends thus remain unpaired, and over time these ends may get progressively shorter as cells continue to divide.\r\n\r\nThe ends of the linear chromosomes are known as\u00a0<strong>telomeres<\/strong>, which have repetitive sequences that code for no particular gene. In a way, these telomeres protect the genes from getting deleted as cells continue to divide. In humans, a six base pair sequence, TTAGGG, is repeated 100 to 1000 times. The discovery of the enzyme telomerase (Figure 1) helped in the understanding of how chromosome ends are maintained. The <strong>telomerase<\/strong> enzyme contains a catalytic part and a built-in RNA template. It attaches to the end of the chromosome, and complementary bases to the RNA template are added on the 3\u2032 end of the DNA strand. Once the 3\u2032 end of the lagging strand template is sufficiently elongated, DNA polymerase can add the nucleotides complementary to the ends of the chromosomes. Thus, the ends of the chromosomes are replicated.\r\n\r\n[caption id=\"attachment_1432\" align=\"aligncenter\" width=\"544\"]<img class=\"size-full wp-image-1432\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/110\/2016\/05\/02184502\/Figure_14_05_01.jpg\" alt=\"Telomerase has an associated RNA that complements the 5 prime overhang at the end of the chromosome. The RNA template is used to synthesize the complementary strand. Telomerase then shifts, and the process is repeated. Next, primase and DNA polymerase synthesize the rest of the complementary strand.\" width=\"544\" height=\"694\" \/> Figure 1. The ends of linear chromosomes are maintained by the action of the telomerase enzyme.[\/caption]\r\n\r\n[caption id=\"attachment_1434\" align=\"alignright\" width=\"300\"]<img class=\"wp-image-1434\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/110\/2016\/05\/02184543\/Figure_14_05_02.jpg\" alt=\"Photo of Elizabeth Blackburn.\" width=\"300\" height=\"223\" \/> Figure 2. Elizabeth Blackburn, 2009 Nobel Laureate, is the scientist who discovered how telomerase works. (credit: US Embassy Sweden)[\/caption]\r\n\r\nTelomerase is typically active in germ cells and adult stem cells. It is not active in adult somatic cells. For her discovery of telomerase and its action, Elizabeth Blackburn (Figure 2) received the Nobel Prize for Medicine and Physiology in 2009.\r\n<h2>Telomerase and Aging<\/h2>\r\nCells that undergo cell division continue to have their telomeres shortened because most somatic cells do not make telomerase. This essentially means that telomere shortening is associated with aging. With the advent of modern medicine, preventative health care, and healthier lifestyles, the human life span has increased, and there is an increasing demand for people to look younger and have a better quality of life as they grow older.\r\n\r\nIn 2010, scientists found that telomerase can reverse some age-related conditions in mice. This may have potential in regenerative medicine.[footnote]Jaskelioff et al., \u201cTelomerase reactivation reverses tissue degeneration in aged telomerase-deficient mice,\u201d <em>Nature<\/em> 469 (2011): 102\u20137.[\/footnote]\u00a0Telomerase-deficient mice were used in these studies; these mice have tissue atrophy, stem cell depletion, organ system failure, and impaired tissue injury responses. Telomerase reactivation in these mice caused extension of telomeres, reduced DNA damage, reversed neurodegeneration, and improved the function of the testes, spleen, and intestines. Thus, telomere reactivation may have potential for treating age-related diseases in humans.\r\n\r\nCancer is characterized by uncontrolled cell division of abnormal cells. The cells accumulate mutations, proliferate uncontrollably, and can migrate to different parts of the body through a process called metastasis. Scientists have observed that cancerous cells have considerably shortened telomeres and that telomerase is active in these cells. Interestingly, only after the telomeres were shortened in the cancer cells did the telomerase become active. If the action of telomerase in these cells can be inhibited by drugs during cancer therapy, then the cancerous cells could potentially be stopped from further division.\r\n<div class=\"textbox learning-objectives\">\r\n<h3>In Summary: Telomeres<\/h3>\r\nThe ends of the chromosomes pose a problem during DNA replication as polymerase is unable to extend them without a primer. Telomerase, an enzyme with a built-in RNA template, extends the ends by copying the RNA template and extending one end of the chromosome. DNA polymerase can then extend the DNA using the primer. In this way, the ends of the chromosomes are protected. This is important as evidence indicates telomere length may play a role in regulating cell division and the process of aging.\r\n\r\n<\/div>\r\n<div class=\"textbox tryit\">\r\n<h3>Try It<\/h3>\r\nhttps:\/\/assess.lumenlearning.com\/practice\/5a4f6639-1238-4809-962c-bb23e41e2caa\r\n<\/div>","rendered":"<div class=\"textbox learning-objectives\">\n<h3>Learning Outcomes<\/h3>\n<ul>\n<li>Understand the basic role of telomeres in protecting DNA from replication errors<\/li>\n<\/ul>\n<\/div>\n<p>As you&#8217;ve learned, the enzyme DNA pol can add nucleotides only in the 5\u2032 to 3\u2032 direction. In the leading strand, synthesis continues until the end of the chromosome is reached. On the lagging strand, DNA is synthesized in short stretches, each of which is initiated by a separate primer. When the replication fork reaches the end of the linear chromosome, there is no place for a primer to be made for the DNA fragment to be copied at the end of the chromosome. These ends thus remain unpaired, and over time these ends may get progressively shorter as cells continue to divide.<\/p>\n<p>The ends of the linear chromosomes are known as\u00a0<strong>telomeres<\/strong>, which have repetitive sequences that code for no particular gene. In a way, these telomeres protect the genes from getting deleted as cells continue to divide. In humans, a six base pair sequence, TTAGGG, is repeated 100 to 1000 times. The discovery of the enzyme telomerase (Figure 1) helped in the understanding of how chromosome ends are maintained. The <strong>telomerase<\/strong> enzyme contains a catalytic part and a built-in RNA template. It attaches to the end of the chromosome, and complementary bases to the RNA template are added on the 3\u2032 end of the DNA strand. Once the 3\u2032 end of the lagging strand template is sufficiently elongated, DNA polymerase can add the nucleotides complementary to the ends of the chromosomes. Thus, the ends of the chromosomes are replicated.<\/p>\n<div id=\"attachment_1432\" style=\"width: 554px\" class=\"wp-caption aligncenter\"><img loading=\"lazy\" decoding=\"async\" aria-describedby=\"caption-attachment-1432\" class=\"size-full wp-image-1432\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/110\/2016\/05\/02184502\/Figure_14_05_01.jpg\" alt=\"Telomerase has an associated RNA that complements the 5 prime overhang at the end of the chromosome. The RNA template is used to synthesize the complementary strand. Telomerase then shifts, and the process is repeated. Next, primase and DNA polymerase synthesize the rest of the complementary strand.\" width=\"544\" height=\"694\" \/><\/p>\n<p id=\"caption-attachment-1432\" class=\"wp-caption-text\">Figure 1. The ends of linear chromosomes are maintained by the action of the telomerase enzyme.<\/p>\n<\/div>\n<div id=\"attachment_1434\" style=\"width: 310px\" class=\"wp-caption alignright\"><img loading=\"lazy\" decoding=\"async\" aria-describedby=\"caption-attachment-1434\" class=\"wp-image-1434\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/110\/2016\/05\/02184543\/Figure_14_05_02.jpg\" alt=\"Photo of Elizabeth Blackburn.\" width=\"300\" height=\"223\" \/><\/p>\n<p id=\"caption-attachment-1434\" class=\"wp-caption-text\">Figure 2. Elizabeth Blackburn, 2009 Nobel Laureate, is the scientist who discovered how telomerase works. (credit: US Embassy Sweden)<\/p>\n<\/div>\n<p>Telomerase is typically active in germ cells and adult stem cells. It is not active in adult somatic cells. For her discovery of telomerase and its action, Elizabeth Blackburn (Figure 2) received the Nobel Prize for Medicine and Physiology in 2009.<\/p>\n<h2>Telomerase and Aging<\/h2>\n<p>Cells that undergo cell division continue to have their telomeres shortened because most somatic cells do not make telomerase. This essentially means that telomere shortening is associated with aging. With the advent of modern medicine, preventative health care, and healthier lifestyles, the human life span has increased, and there is an increasing demand for people to look younger and have a better quality of life as they grow older.<\/p>\n<p>In 2010, scientists found that telomerase can reverse some age-related conditions in mice. This may have potential in regenerative medicine.<a class=\"footnote\" title=\"Jaskelioff et al., \u201cTelomerase reactivation reverses tissue degeneration in aged telomerase-deficient mice,\u201d Nature 469 (2011): 102\u20137.\" id=\"return-footnote-2532-1\" href=\"#footnote-2532-1\" aria-label=\"Footnote 1\"><sup class=\"footnote\">[1]<\/sup><\/a>\u00a0Telomerase-deficient mice were used in these studies; these mice have tissue atrophy, stem cell depletion, organ system failure, and impaired tissue injury responses. Telomerase reactivation in these mice caused extension of telomeres, reduced DNA damage, reversed neurodegeneration, and improved the function of the testes, spleen, and intestines. Thus, telomere reactivation may have potential for treating age-related diseases in humans.<\/p>\n<p>Cancer is characterized by uncontrolled cell division of abnormal cells. The cells accumulate mutations, proliferate uncontrollably, and can migrate to different parts of the body through a process called metastasis. Scientists have observed that cancerous cells have considerably shortened telomeres and that telomerase is active in these cells. Interestingly, only after the telomeres were shortened in the cancer cells did the telomerase become active. If the action of telomerase in these cells can be inhibited by drugs during cancer therapy, then the cancerous cells could potentially be stopped from further division.<\/p>\n<div class=\"textbox learning-objectives\">\n<h3>In Summary: Telomeres<\/h3>\n<p>The ends of the chromosomes pose a problem during DNA replication as polymerase is unable to extend them without a primer. Telomerase, an enzyme with a built-in RNA template, extends the ends by copying the RNA template and extending one end of the chromosome. DNA polymerase can then extend the DNA using the primer. In this way, the ends of the chromosomes are protected. This is important as evidence indicates telomere length may play a role in regulating cell division and the process of aging.<\/p>\n<\/div>\n<div class=\"textbox tryit\">\n<h3>Try It<\/h3>\n<p>\t<iframe id=\"assessment_practice_5a4f6639-1238-4809-962c-bb23e41e2caa\" class=\"resizable\" src=\"https:\/\/assess.lumenlearning.com\/practice\/5a4f6639-1238-4809-962c-bb23e41e2caa?iframe_resize_id=assessment_practice_id_5a4f6639-1238-4809-962c-bb23e41e2caa\" 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-2532\">\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><hr class=\"before-footnotes clear\" \/><div class=\"footnotes\"><ol><li id=\"footnote-2532-1\">Jaskelioff et al., \u201cTelomerase reactivation reverses tissue degeneration in aged telomerase-deficient mice,\u201d <em>Nature<\/em> 469 (2011): 102\u20137. <a href=\"#return-footnote-2532-1\" class=\"return-footnote\" aria-label=\"Return to footnote 1\">&crarr;<\/a><\/li><\/ol><\/div>","protected":false},"author":17,"menu_order":11,"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":"3f63aa33-2958-4974-b29d-bbc2e4416474, b423cbc0-fff6-4720-b445-cda5b714d4ce","pb_show_title":"on","pb_short_title":"","pb_subtitle":"","pb_authors":[],"pb_section_license":""},"chapter-type":[],"contributor":[],"license":[],"class_list":["post-2532","chapter","type-chapter","status-publish","hentry"],"part":297,"_links":{"self":[{"href":"https:\/\/courses.lumenlearning.com\/wm-biology1\/wp-json\/pressbooks\/v2\/chapters\/2532","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/courses.lumenlearning.com\/wm-biology1\/wp-json\/pressbooks\/v2\/chapters"}],"about":[{"href":"https:\/\/courses.lumenlearning.com\/wm-biology1\/wp-json\/wp\/v2\/types\/chapter"}],"author":[{"embeddable":true,"href":"https:\/\/courses.lumenlearning.com\/wm-biology1\/wp-json\/wp\/v2\/users\/17"}],"version-history":[{"count":11,"href":"https:\/\/courses.lumenlearning.com\/wm-biology1\/wp-json\/pressbooks\/v2\/chapters\/2532\/revisions"}],"predecessor-version":[{"id":5968,"href":"https:\/\/courses.lumenlearning.com\/wm-biology1\/wp-json\/pressbooks\/v2\/chapters\/2532\/revisions\/5968"}],"part":[{"href":"https:\/\/courses.lumenlearning.com\/wm-biology1\/wp-json\/pressbooks\/v2\/parts\/297"}],"metadata":[{"href":"https:\/\/courses.lumenlearning.com\/wm-biology1\/wp-json\/pressbooks\/v2\/chapters\/2532\/metadata\/"}],"wp:attachment":[{"href":"https:\/\/courses.lumenlearning.com\/wm-biology1\/wp-json\/wp\/v2\/media?parent=2532"}],"wp:term":[{"taxonomy":"chapter-type","embeddable":true,"href":"https:\/\/courses.lumenlearning.com\/wm-biology1\/wp-json\/pressbooks\/v2\/chapter-type?post=2532"},{"taxonomy":"contributor","embeddable":true,"href":"https:\/\/courses.lumenlearning.com\/wm-biology1\/wp-json\/wp\/v2\/contributor?post=2532"},{"taxonomy":"license","embeddable":true,"href":"https:\/\/courses.lumenlearning.com\/wm-biology1\/wp-json\/wp\/v2\/license?post=2532"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}