{"id":1447,"date":"2020-08-07T00:10:49","date_gmt":"2020-08-07T00:10:49","guid":{"rendered":"https:\/\/meddists.com\/learn\/pre-clinical\/medical-genetics\/mutations-and-repair\/"},"modified":"2021-01-31T23:33:46","modified_gmt":"2021-01-31T22:33:46","slug":"mutations-and-repair","status":"publish","type":"page","link":"https:\/\/meddists.com\/learn\/pre-clinical\/medical-genetics\/mutations-and-repair\/","title":{"rendered":"Mutations and Repair"},"content":{"rendered":"<span class=\"block-heading\" id=\"header_1\">\n<h2 class=\"wp-block-heading\" class=\"wp-block-heading\" class=\"title_collection title1\">What are mutations?<\/h2>\n<\/span><span class=\"block-content\" id=\"contents_1\">\n\n\n<p class=\"wp-block-paragraph\"><div class=\"intro\">Mutations are irreversible changes in the DNA sequence or chromosome structure. Mutations can be Loss of function or Gain of function mutations.<\/div><\/p>\n\n\n<\/span><span class=\"block-heading\" id=\"header_2\">\n<h4 class=\"wp-block-heading\" class=\"wp-block-heading\" class=\"title_collection title3\">Loss of function mutations<\/h4>\n<\/span><span class=\"block-content\" id=\"contents_2\">\n\n\n<p class=\"wp-block-paragraph\">This is the kind of mutation that causes the gene to be underexpressed or not expressed at all. It can be<\/p>\n\n\n\n<ul class=\"wp-block-list\"><li><strong>Recessive:<\/strong> both of the alleles have to have a loss of function mutation for it to be non-functional.<\/li><\/ul>\n\n\n\n<p class=\"wp-block-paragraph\">If one of the alleles is mutated, the other can retain function e.g in tumour suppressor genes; unlike proto-oncogenes; where a gain of function mutation of one of the alleles is sufficient enough to transform the cell.<\/p>\n\n\n\n<ul class=\"wp-block-list\"><li><strong>Dominant Negative:<\/strong> in proteins with more than one subunit, if one of the subunits is non-functional, the whole complex is non-functional.<\/li><\/ul>\n\n\n<\/span><span class=\"block-heading\" id=\"header_3\">\n<h4 class=\"wp-block-heading\" class=\"wp-block-heading\" class=\"title_collection title3\">Gain of function mutations<\/h4>\n<\/span><span class=\"block-content\" id=\"contents_3\">\n\n\n<p class=\"wp-block-paragraph\">This is when the mutation causes the gene to be <strong>expressed more than normal<\/strong>, <strong>with a stronger activity<\/strong> or at the <strong>wrong time and location<\/strong>.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">An example is the conversion of proto-oncogenes to oncogenes. Here, a mutation in one chromosome is enough to be expressed i.e heterozygous organisms will express overexpression unlike in tumour suppressor genes.<\/p>\n\n\n<\/span><span class=\"block-heading\" id=\"header_4\">\n<h2 class=\"wp-block-heading\" class=\"wp-block-heading\" class=\"title_collection title1\">Classification of mutations<\/h2>\n<\/span><span class=\"block-content\" id=\"contents_4\">\n\n\n<p class=\"wp-block-paragraph\">Mutations can be classified based on;<\/p>\n\n\n\n<ol class=\"wp-block-list\"><li><strong>What cells they happen in:<\/strong> It can be in somatic cells(not passed down to offspring) or germ cells(can be passed down to offspring)<\/li><li><strong>The cause of the mutation:<\/strong> can be spontaneous or induced. Spontaneous mutations are caused by <strong>errors in DNA replication and repair<\/strong> and <strong>tautomerism(keto to enol transition)<\/strong>. Induced mutations are caused by mutagenic substances such as <strong>carcinogenic chemicals, UV rays, ionizing radiation<\/strong> and <strong>alkylating agents<\/strong>.<\/li><li><strong>The size of the affected gene:<\/strong><\/li><\/ol>\n\n\n\n<ul class=\"wp-block-list\"><li><strong>Mutations in one base<\/strong><\/li><\/ul>\n\n\n\n<p class=\"wp-block-paragraph\">These are known as <strong>point mutations.<\/strong><\/p>\n\n\n\n<ul class=\"wp-block-list\"><li>They can go unnoticed due to degeneracy of codon(codons are discussed in detail in the Medical Genetics I course) i.e <strong>silent mutations<\/strong><\/li><li>They can cause a change in the amino acid i.e <strong>missense mutations<\/strong><\/li><li>They can lead to a stop codon i.e <strong>nonsense mutations<\/strong><\/li><li>They can affect the whole amino acid sequence i.e the <strong>frameshift mutations<\/strong>.<\/li><li>It can be a <strong>transition<\/strong>; a mutation that causes a change from a purine to purine or pyrimidine to pyrimidine or a <strong>transversion<\/strong> i.e purine to pyrimidine and vice versa.<\/li><\/ul>\n\n\n\n<div class=\"wp-block-image\"><figure class=\"aligncenter\"><a href=\"https:\/\/meddists.com\/wp-content\/uploads\/2020\/03\/Point_mutations-en.png\" target=\"_blank\" title=\"Mutations and Repair\"><img decoding=\"async\" src=\"https:\/\/meddists.com\/wp-content\/uploads\/2020\/03\/Point_mutations-en-600x319.png\" alt=\"\" class=\"wp-image-27253\"\/><\/a><figcaption><strong>Three of the four types of point mutations. In silent mutations, there is no change in the amino acid coded, in nonsense mutation, a STOP codon is coded instead of amino acid and in missense mutation, a different amino acid is coded.<\/strong> (Credit: Jonsta247, CC BY-SA 4.0)<\/figcaption><\/figure><\/div>\n\n\n\n<div class=\"wp-block-image\"><figure class=\"aligncenter\"><a href=\"https:\/\/meddists.com\/wp-content\/uploads\/2020\/03\/Frameshift_mutations_13080927393.jpg\" target=\"_blank\" title=\"Mutations and Repair\"><img decoding=\"async\" src=\"https:\/\/meddists.com\/wp-content\/uploads\/2020\/03\/Frameshift_mutations_13080927393-600x424.jpg\" alt=\"\" class=\"wp-image-27210\"\/><\/a><figcaption><strong>Frameshift mutation. Removal of an Adenine base in the DNA that leads to removal of a Uracil base in the RNA sequence. This will affect the whole codon reading and the amino acids synthesized<\/strong>(Credit: Genomics Education Programme, Frameshift mutations, CC BY 2.0)<\/figcaption><\/figure><\/div>\n\n\n\n<ul class=\"wp-block-list\"><li><strong>Mutations in more than one base<\/strong> i.e a certain region of DNA or a whole chromosome<\/li><\/ul>\n\n\n<\/span><span class=\"block-heading\" id=\"header_5\">\n<h2 class=\"wp-block-heading\" class=\"wp-block-heading\" class=\"title_collection title1\">Important things to note<\/h2>\n<\/span><span class=\"block-content\" id=\"contents_5\">\n\n<\/span><span class=\"block-heading\" id=\"header_6\">\n<h4 class=\"wp-block-heading\" class=\"wp-block-heading\" class=\"title_collection title3\">DNA damage vs DNA mutation<\/h4>\n<\/span><span class=\"block-content\" id=\"contents_6\">\n\n\n<p class=\"wp-block-paragraph\">DNA damage can be repaired but a mutation cannot. It is irreversible. A mutation is DNA damage that could not be fixed.<\/p>\n\n\n<\/span><span class=\"block-heading\" id=\"header_7\">\n<h4 class=\"wp-block-heading\" class=\"wp-block-heading\" class=\"title_collection title3\">Dynamic mutations<\/h4>\n<\/span><span class=\"block-content\" id=\"contents_7\">\n\n\n<p class=\"wp-block-paragraph\">These are trinucleotide repeat expansions i.e if a certain region of DNA, say, CGG is repeated 2-60 times in the DNA normally and it gets repeated more than this, it is called a dynamic mutation.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">Examples of diseases caused by dynamic mutations are Huntington&#8217;s and Fragile X disease.<\/p>\n\n\n<\/span><span class=\"block-heading\" id=\"header_8\">\n<h4 class=\"wp-block-heading\" class=\"wp-block-heading\" class=\"title_collection title3\">Suppressor mutation<\/h4>\n<\/span><span class=\"block-content\" id=\"contents_8\">\n\n\n<p class=\"wp-block-paragraph\">This is when a second mutation that happens in an already mutated gene partially or fully restores the original function i.e like a correctional mutation.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">The suppressor mutation can be<\/p>\n\n\n\n<ul class=\"wp-block-list\"><li>in the same gene (intragenic suppression)<\/li><li>in a different gene(intergenic suppression)<\/li><\/ul>\n<\/span><div id=\"the_titles\" style=\"display:none;\"><h2 class=\"wp-block-heading\" class=\"wp-block-heading\">What are mutations?<\/h2><h4 class=\"wp-block-heading\" class=\"wp-block-heading\">Loss of function mutations<\/h4><h4 class=\"wp-block-heading\" class=\"wp-block-heading\">Gain of function mutations<\/h4><h2 class=\"wp-block-heading\" class=\"wp-block-heading\">Classification of mutations<\/h2><h2 class=\"wp-block-heading\" class=\"wp-block-heading\">Important things to note<\/h2><h4 class=\"wp-block-heading\" class=\"wp-block-heading\">DNA damage vs DNA mutation<\/h4><h4 class=\"wp-block-heading\" class=\"wp-block-heading\">Dynamic mutations<\/h4><h4 class=\"wp-block-heading\" class=\"wp-block-heading\">Suppressor mutation<\/h4><\/div>","protected":false},"excerpt":{"rendered":"<p>What are mutations? Loss of function mutations This is the kind of mutation that causes the gene to be underexpressed or not expressed at all. It can be Recessive: both of the alleles have to have a loss of function mutation for it to be non-functional. If one of the alleles is mutated, the other [&hellip;]<\/p>\n","protected":false},"author":1,"featured_media":0,"parent":1343,"menu_order":6,"comment_status":"closed","ping_status":"closed","template":"","meta":{"footnotes":""},"class_list":["post-1447","page","type-page","status-publish","hentry"],"yoast_head":"<!-- This site is optimized with the Yoast SEO plugin v28.0 - https:\/\/yoast.com\/product\/yoast-seo-wordpress\/ -->\n<title>Mutations and Repair &#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\/\" \/>\n<meta name=\"twitter:label1\" content=\"Est. reading time\" \/>\n\t<meta name=\"twitter:data1\" content=\"4 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\\\/\",\"url\":\"https:\\\/\\\/meddists.com\\\/learn\\\/pre-clinical\\\/medical-genetics\\\/mutations-and-repair\\\/\",\"name\":\"Mutations and Repair &#8211; 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