{"id":768,"date":"2026-06-08T02:29:14","date_gmt":"2026-06-08T06:29:14","guid":{"rendered":""},"modified":"2026-08-08T13:13:42","modified_gmt":"2026-08-08T13:13:42","slug":"dna-repair-ii","status":"publish","type":"post","link":"https:\/\/aboutyou.name\/?p=768","title":{"rendered":"DNA Repair II"},"content":{"rendered":"<p style=\"text-align: center;\"><span style=\"color: #006699;\"><strong><span style=\"6px;\"><span style=\"font-family: Verdana;\"><span style=\"color: #ffd700;\">DNA Mis-Match Repair (MMR)<\/span><\/span><\/span><\/strong><\/span><\/p>\n<p style=\"text-align: left;\"><span style=\"6px;\"><span style=\"font-family: Verdana;\">The DNA Mis-Match Repair (MMR) pathway has evolved to correct errors made by DNA polymerase during DNA replication. Such errors fall into two broad categories:<br \/>\n<\/span><\/span><\/p>\n<ol>\n<li><span style=\"6px; color: #ffd700;\"><span style=\"font-family: Verdana;\">base substitutions, and <\/span><\/span><\/li>\n<li><span style=\"6px; color: #ffd700;\"><span style=\"font-family: Verdana;\">insertions\/deletions.<\/span><\/span><\/li>\n<\/ol>\n<p><span style=\"6px;\"><span style=\"font-family: Verdana;\">1. <span style=\"color: #ffd700;\">A base substitution error<\/span> occurs when DNA polymerase inserts an incorrect nucleotide opposite the template base, like a T opposite G instead of C, or A opposite C instead of G. <\/span><\/span><\/p>\n<p><span style=\"6px;\"><span style=\"font-family: Verdana;\">These incorrect base pairs are referred to as mismatches. Often, DNA polymerase will make an error when copying a base that has been distorted by <a href=\"?p=766\"><span style=\"color: #ffd700;\">alkylation<\/span><\/a>, such as inserting a T opposite O<sub>6<\/sub>-methyl-Guanine on the other strand.<\/span><\/span><\/p>\n<p style=\"text-align: center;\"><iframe loading=\"lazy\" title=\"YouTube video player\" src=\"https:\/\/www.youtube.com\/embed\/HYS6EKnQcv0?si=7JHC1Kdli6wVf8E4\" width=\"280\" height=\"155\" frameborder=\"0\" allowfullscreen=\"allowfullscreen\"><\/iframe><\/p>\n<p><span style=\"6px;\"><span style=\"font-family: Verdana;\">2.<span style=\"color: #ffd700;\"> An insertion error<\/span> occurs when DNA polymerase adds several extra nucleotides to a sequence; a <span style=\"color: #ffd700;\">deletion error<\/span> is made when several nucleotides are omitted from a sequence. Sequences that contain repeats of the same nucleotide such as AAAAAA, are very vulnerable to these type of errors.<\/span><\/span><\/p>\n<p><span style=\"6px;\"><span style=\"font-family: Verdana;\">Other repetitive sequences, like the di-nucleotide repeat CACACACA and the tri-nucleotide repeat CTGCTGCTG, are prone to insertion\/deletion errors as well. These ones are called micro-satellites.<\/span><\/span><\/p>\n<p><span style=\"6px;\"><span style=\"font-family: Verdana;\">Defects in DNA mismatch repair have been found in different types of cancer. Shorter or longer micro-satellite sequences are typical of defective MMR. <\/span><\/span><\/p>\n<p><span style=\"6px;\"><span style=\"font-family: Verdana;\">Expansion of tri-nucleotide repeat sequences is linked to various hereditary neurological disorders, like myotonic dystrophy and Huntington&#8217;s disease.<\/span><\/span><\/p>\n<p><span style=\"6px;\"><span style=\"font-family: Verdana;\">The process of MMR is like the BER and NER pathways:<br \/>\n<\/span><\/span><\/p>\n<ol>\n<li><span style=\"6px;\"><span style=\"font-family: Verdana;\">a mismatch must be recognized by a group of proteins that specialize in that particular type of distortion, <\/span><\/span><\/li>\n<li><span style=\"6px;\"><span style=\"font-family: Verdana;\">a phospho-diester bond in the DNA strand containing the mismatched nucleotide is cleaved, then displaced by DNA helicase, and then removed,<br \/>\n<\/span><\/span><\/li>\n<li><span style=\"6px;\"><span style=\"font-family: Verdana;\">DNA polymerase carries out the DNA repair synthesis, <\/span><\/span><\/li>\n<li><span style=\"6px;\"><span style=\"font-family: Verdana;\">DNA ligase restores the sugar-phosphate backbone. <\/span><\/span><\/li>\n<\/ol>\n<p><span style=\"6px;\"><span style=\"font-family: Verdana;\">The patch of DNA newly synthesized by the MMR DNA polymerase is about 1,000 nucleotides long, compared to BER, which typically replaces 1 nucleotide, or NER, which replaces about 30 nucleotides. <\/span><\/span><\/p>\n<p><span style=\"6px;\"><span style=\"font-family: Verdana;\">MMR is especially important in tissues that are constantly regenerating, like the lining of the uterus and the intestines.<\/span><\/span><\/p>\n<p style=\"text-align: center;\"><img loading=\"lazy\" decoding=\"async\" class=\"aligncenter\" src=\"\/userfiles\/image\/2014%20pics\/CRISPR.jpg\" alt=\"\" width=\"222\" height=\"140\" \/><\/p>\n<p><span style=\"6px;\"><span style=\"font-family: Verdana;\">Certain bacterial cells can identify invading viruses and chop up their DNA. CRISPR-Cas9 adapts that technique to allow us to edit genes nad remove harmful diseases.<\/span><\/span><\/p>\n<p><span style=\"font-family: Verdana; 6px;\">Cas9 is a modified protein injected into a body to work on the DNA, like scissors that can snip the genes.<\/span><\/p>\n<p style=\"text-align: right;\"><a href=\"?p=629\"><span style=\"2px;\"><span style=\"font-family: Verdana;\"><strong><span style=\"color: #ffd700;\">read more &#8230;<\/span><\/strong><\/span><\/span><\/a><\/p>\n<p style=\"text-align: right;\">\n","protected":false},"excerpt":{"rendered":"<p>DNA Mis-Match Repair (MMR) The DNA Mis-Match Repair (MMR) pathway has evolved to correct errors made by DNA polymerase during DNA replication. Such errors fall into two broad categories: base substitutions, and insertions\/deletions. 1. A base substitution error occurs when DNA polymerase inserts an incorrect nucleotide opposite the template base, like a T opposite G&#8230;<\/p>\n","protected":false},"author":1,"featured_media":1769,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"_kad_post_transparent":"default","_kad_post_title":"default","_kad_post_layout":"default","_kad_post_sidebar_id":"","_kad_post_content_style":"default","_kad_post_vertical_padding":"default","_kad_post_feature":"","_kad_post_feature_position":"","_kad_post_header":false,"_kad_post_footer":false,"_kad_post_classname":"","footnotes":""},"categories":[1],"tags":[],"class_list":["post-768","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-uncategorized"],"_links":{"self":[{"href":"https:\/\/aboutyou.name\/index.php?rest_route=\/wp\/v2\/posts\/768","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/aboutyou.name\/index.php?rest_route=\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/aboutyou.name\/index.php?rest_route=\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/aboutyou.name\/index.php?rest_route=\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/aboutyou.name\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=768"}],"version-history":[{"count":6,"href":"https:\/\/aboutyou.name\/index.php?rest_route=\/wp\/v2\/posts\/768\/revisions"}],"predecessor-version":[{"id":9756,"href":"https:\/\/aboutyou.name\/index.php?rest_route=\/wp\/v2\/posts\/768\/revisions\/9756"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/aboutyou.name\/index.php?rest_route=\/wp\/v2\/media\/1769"}],"wp:attachment":[{"href":"https:\/\/aboutyou.name\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=768"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/aboutyou.name\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=768"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/aboutyou.name\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=768"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}