{"id":767,"date":"2026-06-08T02:29:14","date_gmt":"2026-06-08T06:29:14","guid":{"rendered":""},"modified":"2026-06-08T02:29:14","modified_gmt":"2026-06-08T06:29:14","slug":"dna-repair-i","status":"publish","type":"post","link":"https:\/\/c2creset.ondigit.us\/?p=767","title":{"rendered":"DNA Repair I"},"content":{"rendered":"<p style=\"text-align: center;\"><span style=\"color: rgb(0, 102, 153);\"><strong><span style=\"font-size: small;\"><span style=\"font-family: Verdana;\">DNA Repair I<\/span><\/span><\/strong><\/span><span style=\"font-size: small;\"><span style=\"font-family: Verdana;\"><br \/>\n<\/span><\/span><\/p>\n<p style=\"text-align: center;\"><span style=\"color: rgb(0, 102, 153);\"><strong><span style=\"font-size: small;\"><span style=\"font-family: Verdana;\">Base Excision Repair (BER)<\/span><\/span><\/strong><\/span><\/p>\n<p style=\"text-align: left;\"><span style=\"font-size: small;\"><span style=\"font-family: Verdana;\">The basic steps of the BER pathway are:<br \/>\n1.\tDistortion recognition,<br \/>\n2.\tBase excision, <br \/>\n3.\tAP-site incision, <br \/>\n4.\tDNA repair synthesis, <br \/>\n5.\tDNA ligation.<br \/>\n<\/span><\/span><\/p>\n<p style=\"text-align: center;\"><iframe loading=\"lazy\" height=\"160\" frameborder=\"0\" width=\"260\" allowfullscreen=\"\" src=\"http:\/\/www.youtube.com\/embed\/g4khROaOO6c\"><\/iframe><\/p>\n<p style=\"text-align: left;\"><span style=\"font-size: small;\"><span style=\"font-family: Verdana;\">DNA bases that have been modified by the addition or loss of a small chemical group as described above are repaired by the BER pathway (see video above). The BER pathway begins with the removal of a distorted base by an enzyme called DNA glycosylase.<\/span><\/span><\/p>\n<p><span style=\"font-size: small;\"><span style=\"font-family: Verdana;\">They remove the damaged nitrogenous base while leaving the sugar-phosphate backbone intact, thus creating an apurinic\/apyrimidinic site, commonly referred to as <a href=\"http:\/\/en.wikipedia.org\/wiki\/AP_site\"><span style=\"color: rgb(0, 0, 255);\">an AP site<\/span><\/a>. <\/span><\/span><\/p>\n<p><span style=\"font-size: small;\"><span style=\"font-family: Verdana;\">Then, an enzyme specialized in synthesizing DNA, called a DNA polymerase, will first remove the now baseless sugar phosphate and then insert the correct nucleotide (C or G) to the complementary base on the strand. <\/span><\/span><\/p>\n<p><span style=\"font-size: small;\"><span style=\"font-family: Verdana;\">The final step in the BER pathway is to tie the DNA strands on both sides of the nick caused by the repair. The sugars that carry the DNA bases are linked together by phosphate groups. The enzyme DNA ligase joins them again by creating a phosphodiester bond between them, sealing the nick.<\/span><\/span><\/p>\n<p><span style=\"font-size: small;\"><span style=\"font-family: Verdana;\">A <a href=\"?p=597\"><span style=\"color: rgb(0, 0, 255);\">phosphodiester bond<\/span><\/a> is a<\/span><\/span><span style=\"font-size: small;\"><span style=\"font-family: Verdana;\"> covalent chemical bond that holds together the polynucleotide chains of RNA and DNA by joining a carbon in the pentose sugar of one nucleotide to a carbon in the pentose sugar of the adjacent nucleotide.<\/span><\/span><\/p>\n<p style=\"text-align: center;\"><span style=\"color: rgb(0, 102, 153);\"><strong><span style=\"font-size: small;\"><span style=\"font-family: Verdana;\">Nucleotide Excision Repair (NER)<\/span><\/span><\/strong><\/span><span style=\"color: rgb(0, 102, 153);\"><strong><span style=\"font-size: small;\"><span style=\"font-family: Verdana;\"><br \/>\n<\/span><\/span><\/strong><\/span><\/p>\n<p style=\"text-align: center;\"><iframe loading=\"lazy\" height=\"160\" frameborder=\"0\" width=\"260\" src=\"http:\/\/www.youtube.com\/embed\/xj32VEkJ5IY\" allowfullscreen=\"\"><\/iframe><\/p>\n<p style=\"text-align: left;\"><span style=\"font-size: small;\"><span style=\"font-family: Verdana;\">DNA damage that significantly distorts the double-stranded structure of DNA, is subject to repair by the nucleotide excision repair (NER) pathway. UV light in sunshine can disturb DNA by forming so called photoproducts. <\/span><\/span><\/p>\n<p style=\"text-align: left;\"><span style=\"font-size: small;\"><span style=\"font-family: Verdana;\">UV radiation excites many types of molecules, causing them to react with each other and with DNA. UV light can catalyze the formation of chemical bonds between <a href=\"?p=623\"><span style=\"color: rgb(0, 0, 255);\">adjacent thymine (T) and cytosine (C) bases<\/span><\/a>. These cross-links distort the double-stranded structure of DNA and block DNA replication.<\/span><\/span><\/p>\n<p style=\"text-align: left;\"><span style=\"font-size: small;\"><span style=\"font-family: Verdana;\">DNA distortion is also caused by organic molecules found in mold-contaminated peanuts, smoke, and soot. Ingestion or inhalation of these and similar compounds activates the body&#8217;s detoxification systems, which convert <a href=\"?p=590\"><span style=\"color: rgb(0, 0, 255);\">hydrophobic<\/span><\/a> organic molecules into water-soluble forms for removal. <\/span><\/span><\/p>\n<p style=\"text-align: left;\"><span style=\"font-size: small;\"><span style=\"font-family: Verdana;\">However, their intermediate forms are very reactive with DNA purines, and form DNA base additions. They can impact <a href=\"?p=405\"><span style=\"color: rgb(0, 0, 255);\">guanine and adenine<\/span><\/a>, block DNA replication, cause mutations and deletions of large segments of DNA, and cell death.<\/span><\/span><\/p>\n<p style=\"text-align: left;\"><span style=\"font-size: small;\"><span style=\"font-family: Verdana;\">The mechanism of NER, involving some 30 proteins, is more complex than that of BER, but the basic principles are similar.<\/span><\/span><span style=\"font-size: small;\"><span style=\"font-family: Verdana;\"><br \/>\n<\/span><\/span><\/p>\n<p style=\"text-align: center;\"><iframe loading=\"lazy\" height=\"160\" frameborder=\"0\" width=\"260\" allowfullscreen=\"\" src=\"http:\/\/www.youtube.com\/embed\/ZKPIr0n99T8\"><\/iframe><\/p>\n<p><span style=\"font-size: small;\"><span style=\"font-family: Verdana;\"><span style=\"color: rgb(0, 0, 255);\">How can a single multi-protein complex detect so many different types of DNA distortion?<\/span><\/span><\/span><\/p>\n<p><span style=\"font-size: small;\"><span style=\"font-family: Verdana;\">The answer is that the DNA damage must:<br \/>\n<\/span><\/span><\/p>\n<ol>\n<li><span style=\"font-size: small;\"><span style=\"font-family: Verdana;\">distort the normal double-stranded structure of DNA, and\/or <\/span><\/span><\/li>\n<li><span style=\"font-size: small;\"><span style=\"font-family: Verdana;\">block <a href=\"?p=620\"><span style=\"color: rgb(0, 0, 255);\">transcription <\/span><\/a>by <a href=\"http:\/\/en.wikipedia.org\/wiki\/RNA_polymerase\"><span style=\"color: rgb(0, 0, 255);\">RNA polymerase<\/span><\/a>. Unusual kinks or twists in double-stranded DNA are recognized by the NER damage-recognition multi-protein complex. They are also recruited when RNA polymerase stalls at a distorted DNA base.<\/span><\/span><\/li>\n<\/ol>\n<p style=\"text-align: left;\"><span style=\"font-size: small;\"><span style=\"font-family: Verdana;\">Next, the double-stranded DNA adjacent to the distortion is unwound by a DNA unwinding enzyme called <a href=\"?p=600\"><span style=\"color: rgb(0, 0, 255);\">Helicase<\/span><\/a>. The distorted strand is then cleaved a few nucleotides after the damage, and about 25 nucleotides before it, by specific endo-nucleases associated with the NER protein complex. <\/span><\/span><\/p>\n<p style=\"text-align: left;\"><span style=\"font-size: small;\"><span style=\"font-family: Verdana;\">Then, the distorted DNA segment is displaced by DNA polymerase and associated proteins, and a corresponding repair patch is synthesized. <\/span><\/span><\/p>\n<p style=\"text-align: left;\"><span style=\"font-size: small;\"><span style=\"font-family: Verdana;\">Lastly, DNA ligase joins the newly synthesized piece of DNA to the pre-existing strand. <\/span><\/span><\/p>\n<p style=\"text-align: center;\"><iframe loading=\"lazy\" height=\"160\" frameborder=\"0\" width=\"260\" allowfullscreen=\"\" src=\"http:\/\/www.youtube.com\/embed\/bgUH9NfO2QM\"><\/iframe><\/p>\n<p style=\"text-align: right;\"><span style=\"font-size: x-small;\"><span style=\"font-family: Verdana;\">&nbsp;<a href=\"?p=768\"><strong><span style=\"color: rgb(0, 0, 255);\">read more &#8230;<\/span><\/strong><\/a><\/span><\/span><\/p>\n<p style=\"text-align: right;\">&nbsp;<\/p>\n","protected":false},"excerpt":{"rendered":"<p>DNA Repair I Base Excision Repair (BER) The basic steps of the BER pathway are: 1. Distortion recognition, 2. Base excision, 3. AP-site incision, 4. DNA repair synthesis, 5. DNA ligation. DNA bases that have been modified by the addition or loss of a small chemical group as described above are repaired by the BER&#8230;<\/p>\n","protected":false},"author":1,"featured_media":1231,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"_kad_post_transparent":"","_kad_post_title":"","_kad_post_layout":"","_kad_post_sidebar_id":"","_kad_post_content_style":"","_kad_post_vertical_padding":"","_kad_post_feature":"","_kad_post_feature_position":"","_kad_post_header":false,"_kad_post_footer":false,"_kad_post_classname":"","footnotes":""},"categories":[],"tags":[],"class_list":["post-767","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry"],"_links":{"self":[{"href":"https:\/\/c2creset.ondigit.us\/index.php?rest_route=\/wp\/v2\/posts\/767","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/c2creset.ondigit.us\/index.php?rest_route=\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/c2creset.ondigit.us\/index.php?rest_route=\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/c2creset.ondigit.us\/index.php?rest_route=\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/c2creset.ondigit.us\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=767"}],"version-history":[{"count":0,"href":"https:\/\/c2creset.ondigit.us\/index.php?rest_route=\/wp\/v2\/posts\/767\/revisions"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/c2creset.ondigit.us\/index.php?rest_route=\/wp\/v2\/media\/1231"}],"wp:attachment":[{"href":"https:\/\/c2creset.ondigit.us\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=767"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/c2creset.ondigit.us\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=767"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/c2creset.ondigit.us\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=767"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}