{"id":1453,"date":"2020-08-07T00:16:24","date_gmt":"2020-08-07T00:16:24","guid":{"rendered":"https:\/\/meddists.com\/learn\/pre-clinical\/medical-genetics\/mutations-and-repair\/repair-of-dna-damage\/"},"modified":"2021-01-31T23:34:21","modified_gmt":"2021-01-31T22:34:21","slug":"repair-of-dna-damage","status":"publish","type":"page","link":"https:\/\/meddists.com\/learn\/pre-clinical\/medical-genetics\/mutations-and-repair\/repair-of-dna-damage\/","title":{"rendered":"Repair of DNA damage"},"content":{"rendered":"\n<p class=\"wp-block-paragraph\"><div class=\"intro\">There are four major ways to repair the damaged DNA;<\/p>\n\n\n\n<ol class=\"wp-block-list\"><li>Base Excision Repair(BER)<\/li><li>Nucleotide Excision Repair(NER)<\/li><li>Mismatch Repair(MMR)<\/li><li>SOS Repair<\/div><\/li><\/ol>\n\n\n<span class=\"block-heading\" id=\"header_1\">\n<h4 class=\"wp-block-heading\" class=\"wp-block-heading\" class=\"title_collection title1\">Base Excision Repair(BER)<\/h4>\n<\/span><span class=\"block-content\" id=\"contents_1\">\n\n\n<p class=\"wp-block-paragraph\">This type of repair is used to fix small sized damages that do not distort the helical structure of the DNA molecule.<\/p>\n\n\n\n<ul class=\"wp-block-list\"><li>It is done by enzymes known as <strong>glycosylases<\/strong> that recognize the damaged base and remove it.<\/li><li>After this, <strong>AP endonucleases<\/strong> are recruited to cleave AP sites.<\/li><li><strong>DNA polymerase<\/strong> adds the missing bases and they are joined together by<strong> ligase<\/strong>.<\/li><\/ul>\n\n\n\n<p class=\"wp-block-paragraph\">Examples of such damages are <strong>deamination, oxidization<\/strong> or <strong>alkylation<\/strong> of a base.<\/p>\n\n\n\n<div class=\"wp-block-image\"><figure class=\"aligncenter\"><a href=\"https:\/\/meddists.com\/wp-content\/uploads\/2020\/03\/774px-Dna_repair_base_excersion_en.svg_.png\" target=\"_blank\" title=\"Repair of DNA damage\"><img decoding=\"async\" src=\"https:\/\/meddists.com\/wp-content\/uploads\/2020\/03\/774px-Dna_repair_base_excersion_en.svg_-454x600.png\" alt=\"\" class=\"wp-image-27083\"\/><\/a><figcaption><strong>A visual illustration of BER<\/strong>(Credit: LadyofHats)<\/figcaption><\/figure><\/div>\n\n\n<\/span><span class=\"block-heading\" id=\"header_2\">\n<h4 class=\"wp-block-heading\" class=\"wp-block-heading\" class=\"title_collection title1\">Nucleotide Excision Repair(NER)<\/h4>\n<\/span><span class=\"block-content\" id=\"contents_2\">\n\n\n<p class=\"wp-block-paragraph\">This type of repair is used to fix large sized damages that distort the helical structure of the DNA molecule.<\/p>\n\n\n\n<ul class=\"wp-block-list\"><li><strong>Endonuclease<\/strong> will cleave the damaged part of the DNA and <strong>helicase<\/strong> will remove it.<\/li><li>After this, <strong>DNA polymerase<\/strong> adds the missing bases and they are joined together by<strong> ligase<\/strong>.<\/li><\/ul>\n\n\n\n<p class=\"wp-block-paragraph\">An example of such damage is the <strong>cross-linking of thymine<\/strong> in the presence of UV rays.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">Failure of this repair system leads to <strong>Xeroderma Pigmentosum<\/strong>; a cancer syndrome<em>(details of cancer syndromes are discussed in the Oncogenetics: Cancer Syndromes course)<\/em>.<\/p>\n\n\n<\/span><span class=\"block-heading\" id=\"header_3\">\n<h4 class=\"wp-block-heading\" class=\"wp-block-heading\" class=\"title_collection title1\">Mismatch Repair(MMR)<\/h4>\n<\/span><span class=\"block-content\" id=\"contents_3\">\n\n\n<p class=\"wp-block-paragraph\">This type of repair is used to fix mismatches in complimentary base pairing i.e when the wrong bases are paired up with each other<em>( Reminder: Adenine pairs with Thymine and Cytosine pairs with Guanine)<\/em>.<\/p>\n\n\n\n<ul class=\"wp-block-list\"><li>The <strong>MutS<\/strong> protein binds to the DNA and searches for mismatches.<\/li><li>When it finds one, it initiates a protein cascade that leads to unwinding and digestion of DNA by <strong>helicase<\/strong> and <strong>exonuclease<\/strong> respectively.<\/li><li>After this, <strong>DNA polymerase<\/strong> adds the missing bases and they are joined together by<strong> ligase<\/strong>.<\/li><\/ul>\n\n\n\n<div class=\"wp-block-image\"><figure class=\"aligncenter\"><a href=\"https:\/\/meddists.com\/wp-content\/uploads\/2020\/03\/DNA_mismatch_repair_Ecoli.png\" target=\"_blank\" title=\"Repair of DNA damage\"><img decoding=\"async\" src=\"https:\/\/meddists.com\/wp-content\/uploads\/2020\/03\/DNA_mismatch_repair_Ecoli.png\" alt=\"\" class=\"wp-image-27094\"\/><\/a><figcaption><strong>MMR in prokaryotic cells(E. coli). A similar process takes place in eukaryotic cells<\/strong>(Credit: Kenji Fukui, CC BY 4.0)<\/figcaption><\/figure><\/div>\n\n\n<\/span><span class=\"block-heading\" id=\"header_4\">\n<h4 class=\"wp-block-heading\" class=\"wp-block-heading\" class=\"title_collection title1\">SOS repair<\/h4>\n<\/span><span class=\"block-content\" id=\"contents_4\">\n\n\n<p class=\"wp-block-paragraph\">This is when DNA is severely and globally damaged.<\/p>\n\n\n\n<ul class=\"wp-block-list\"><li>The cell will halt all DNA replication and initiate repair and apoptosis.<\/li><li>It is used as a last resort.<\/li><li>The cells do not like to use this repair system because, in this process of global repair, some de novo mutations can also happen.<\/li><\/ul>\n\n\n\n<div class=\"wp-block-image\"><figure class=\"aligncenter\"><a href=\"https:\/\/meddists.com\/wp-content\/uploads\/2020\/03\/SOS_repair1.jpeg\" target=\"_blank\" title=\"Repair of DNA damage\"><img decoding=\"async\" src=\"https:\/\/meddists.com\/wp-content\/uploads\/2020\/03\/SOS_repair1-1024x318.jpeg\" alt=\"\" class=\"wp-image-27098\"\/><\/a><figcaption><strong>SOS repair in eukaryotic cells. The DNA damage will induce expression of the RecA protein which reduces expression of the LexA protein and leads to activation of the SOS DNA repair genes<\/strong>(Credit: Sri1989vathsan, CC BY-SA 3.0)<\/figcaption><\/figure><\/div>\n<\/span><div id=\"the_titles\" style=\"display:none;\"><h4 class=\"wp-block-heading\" class=\"wp-block-heading\">Base Excision Repair(BER)<\/h4><h4 class=\"wp-block-heading\" class=\"wp-block-heading\">Nucleotide Excision Repair(NER)<\/h4><h4 class=\"wp-block-heading\" class=\"wp-block-heading\">Mismatch Repair(MMR)<\/h4><h4 class=\"wp-block-heading\" class=\"wp-block-heading\">SOS repair<\/h4><\/div>","protected":false},"excerpt":{"rendered":"<p>Base Excision Repair(BER) This type of repair is used to fix small sized damages that do not distort the helical structure of the DNA molecule. It is done by enzymes known as glycosylases that recognize the damaged base and remove it. After this, AP endonucleases are recruited to cleave AP sites. DNA polymerase adds the [&hellip;]<\/p>\n","protected":false},"author":1,"featured_media":0,"parent":1447,"menu_order":0,"comment_status":"closed","ping_status":"closed","template":"","meta":{"footnotes":""},"class_list":["post-1453","page","type-page","status-publish","hentry"],"yoast_head":"<!-- This site is optimized with the Yoast SEO plugin v27.8 - https:\/\/yoast.com\/product\/yoast-seo-wordpress\/ -->\n<title>Repair of DNA damage &#8211; Meddists<\/title>\n<meta name=\"robots\" content=\"index, follow, max-snippet:-1, max-image-preview:large, max-video-preview:-1\" \/>\n<link rel=\"canonical\" href=\"https:\/\/meddists.com\/learn\/pre-clinical\/medical-genetics\/mutations-and-repair\/repair-of-dna-damage\/\" \/>\n<meta name=\"twitter:label1\" content=\"Est. reading time\" \/>\n\t<meta name=\"twitter:data1\" content=\"3 minutes\" \/>\n<script type=\"application\/ld+json\" class=\"yoast-schema-graph\">{\"@context\":\"https:\\\/\\\/schema.org\",\"@graph\":[{\"@type\":\"WebPage\",\"@id\":\"https:\\\/\\\/meddists.com\\\/learn\\\/pre-clinical\\\/medical-genetics\\\/mutations-and-repair\\\/repair-of-dna-damage\\\/\",\"url\":\"https:\\\/\\\/meddists.com\\\/learn\\\/pre-clinical\\\/medical-genetics\\\/mutations-and-repair\\\/repair-of-dna-damage\\\/\",\"name\":\"Repair of DNA damage &#8211; 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