{"id":1095,"date":"2024-02-21T22:05:54","date_gmt":"2024-02-22T03:05:54","guid":{"rendered":"https:\/\/pressbooks.bccampus.ca\/pathophysiology\/?post_type=chapter&p=1095"},"modified":"2026-01-03T16:16:38","modified_gmt":"2026-01-03T21:16:38","slug":"review-of-dna-transcription-translation-and-types-of-dna-mutations","status":"web-only","type":"chapter","link":"https:\/\/pressbooks.bccampus.ca\/pathophysiology\/chapter\/review-of-dna-transcription-translation-and-types-of-dna-mutations\/","title":{"raw":"Review of DNA Transcription, Translation and Types of DNA Mutations","rendered":"Review of DNA Transcription, Translation and Types of DNA Mutations"},"content":{"raw":"

DNA Transcription and Translation<\/strong><\/h3>\r\nIt is often said that DNA<\/strong> contains the blueprint for the cell as it used to construct enzymes and proteins required for enabling and facilitating cellular reactions, cellular signalling, as well as building cellular components.\u00a0 There are 23 pairs of chromosomes<\/strong> in the human genome containing over 20,000 genes<\/strong> altogether, which are used to code for proteins and peptides.\u00a0 In brief, DNA transcription<\/strong> and translation<\/strong> involves the process of converting genetic information first from DNA into mRNA and then into functional proteins<\/strong>.\u00a0 \u00a0Transcription is the process in which a gene is copied into a complimentary strand of messenger RNA<\/strong> (mRNA).\u00a0 T<\/span>ranslation involves the mRNA sequence of nucleotides being used to string specific amino acids together to form proteins.<\/strong>\u00a0 In this section we will examine how mutations<\/strong> in DNA can affect the proteins being produced.\u00a0 \u00a0<\/span>\r\n\r\n \r\n

The Effects of DNA Mutation on Protein Production<\/strong><\/h3>\r\nAs mentioned in the previous section, mutations<\/strong> in genes can occur due to various factors such as viruses, asbestos, radiation, cigarette smoke,<\/strong> or spontaneous errors during DNA duplication<\/strong>.\u00a0 There are several types of mutations that can occur on a strand of DNA and some can have significant effects, while other may not have any effect at all.\r\n\r\nIn examining the effects of DNA mutations, we need to remember that genes<\/strong> are spread along chromosomes separated by sequences of non-coding regions<\/strong>.\u00a0 These non-coding regions don't code for peptides or proteins, but can play other roles.\u00a0 For example, non-coding regions contain promotor regions<\/strong> that influence the rate of transcription<\/strong> of downstream genes.\u00a0 Some non-coding DNA is used to make non-coding RNA<\/strong> such as transfer RNA (tRNA)<\/strong> and ribosomal RNA (rRNA)<\/strong> molecules.\u00a0 \u00a0There are other non-coding regions that don't appear to have any function at all and is referred to as \"junk DNA\"<\/strong>, though that is currently under investigation as non-coding DNA makes up over 98% of our genome and may be found to have important roles within the cell.\u00a0 One theory is that over the millennia, \"junk DNA\" has accumulated that may originally have had useful purposes, but are no longer required.\u00a0 It may too be that junk DNA has been perpetually inserted into the genome over time and been passed from one generation to the other.\u00a0 Some of this junk DNA likely came has from pre-historic viruses and bacteria.\r\n\r\n \r\n

Point Mutations and Frameshift Mutations and Cancer<\/strong><\/h3>\r\nThere are 3 types of mutations include insertion, substitution,<\/strong> and deletion<\/strong> mutations.\u00a0 Point mutations<\/strong> are the most common type of mutation and involve a substitution of a single nucleotide in DNA.\u00a0 A substitution mutation replaces one nucleotide with another (e.g. CAG to CAT), potentially altering one amino acid in the protein though not always.\u00a0 There are 3 possible outcomes.\u00a0 A point mutation can create a silent, missense<\/strong> or nonsense<\/strong> mutation as shown in the table below.\r\n\r\n\r\n\r\n\r\n\r\n\r\n
Examples of Types of Point Mutation<\/strong><\/td>\r\nDNA Triplet \u2192 Mutated DNA Triplet<\/strong><\/td>\r\nEffect of Amino Acid Codon Sequence on Translated Protein<\/strong><\/td>\r\nCellular Effect<\/strong><\/td>\r\n<\/tr>\r\n
Silent Mutation<\/strong><\/td>\r\nACA \u2192 ACG<\/td>\r\nCysteine \u2192 Cysteine<\/td>\r\nnone<\/td>\r\n<\/tr>\r\n
Missense Mutation<\/strong><\/td>\r\nACA \u2192 ACC<\/span><\/td>\r\nCysteine \u2192 Tryptophan<\/td>\r\nmild to serious<\/td>\r\n<\/tr>\r\n
Nonsense Mutation<\/strong><\/td>\r\nACA \u2192 ACT<\/span><\/td>\r\nCysteine \u2192 Stop<\/td>\r\nserious<\/td>\r\n<\/tr>\r\n<\/tbody>\r\n<\/table>\r\nThe table above gives examples of point mutations that are classified as silent, missense and nonsense depending on the effect on the protein produced.\u00a0 A silent mutation<\/strong> occurs when the nucleotide substitution does not change the amino acid that is coded for and is therefore sometimes called a synonymous<\/strong> mutation.\u00a0 A missense<\/strong> mutation results in a new amino acid being coded for and its effects depend on whether the new amino acid changes the function of the protein or enzyme.\u00a0 There be no effect on the protein\/enzyme's ability to function.\u00a0 However, there may be a loss of function or even a change of function that actively impedes cellular abilities or structure.\u00a0 Nonsense<\/strong> mutations result in a protein or enzyme that is either not functional or actively dysfunctional.\u00a0 In this case, unless the cell produces other similar proteins or enzymes that are able to compensate for this loss, the cell itself could become less functional, function inappropriately, or even die.\u00a0 Due to the difference created in the final peptide sequence, both missense and nonsense mutations are considered nonsynonymous<\/strong> mutations.\r\n\r\nFrameshift mutations<\/strong> occur when a nucleotide is either inserted<\/strong> or deleted<\/strong> within a gene's coding region.\u00a0 As a result, there is a shift in the reading frame affecting the mRNA sequence that is transcribed and then translated.\u00a0 As a result of a frameshift, all of the DNA's reading frames downstream of the mutation will be affected, potentially resulting in every subsequent codon as being different and coding for a different amino acid.\r\n\r\n\r\n\r\n\r\n\r\n\r\n
Examples of Frameshift Mutations<\/strong><\/td>\r\nDNA Triplet Sequence<\/strong><\/td>\r\nmRNA Codon Sequence<\/strong><\/td>\r\nAmino Acid Sequence<\/strong><\/td>\r\n<\/tr>\r\n
Original Sequence<\/strong><\/td>\r\nTAC-CTA-TCT-ACC-A<\/td>\r\nAUG-GAU-AGA-UGG-U<\/td>\r\nMet-Asp-Arg-Trp<\/td>\r\n<\/tr>\r\n
Sequence with Insertion<\/strong><\/td>\r\nTAC-CTT<\/span>-ATC-TAC-C<\/td>\r\nAUG-GAA-UAG-AUG-G<\/td>\r\nMet-Glu-Stop<\/td>\r\n<\/tr>\r\n
Sequence with Deletion<\/strong><\/td>\r\nTAC-CTT-CTA-CCU<\/td>\r\nAUG-GAA-GAU-GGA<\/td>\r\nMet-Glu-Asp-Gly<\/td>\r\n<\/tr>\r\n<\/tbody>\r\n<\/table>\r\nIn the above examples of point mutations and frameshift mutations, it is evident the substitution, insertion or deletion of an amino acid within the coding region can lead to loss of a functional protein or enzyme.\u00a0 In the case of cancer,<\/strong> over 290 gene mutations have been identified which affect the function of key enzymes - most often those involved in regulating the rates of cell cycling, differentiation and apoptosis.\r\n

Chromosomal Alterations<\/strong><\/h3>\r\nChromosomal alterations<\/strong> often result in death of the cell or organism (depending on the stage of development in which it occurs<\/em>) rather than resulting in cancer. Chromosomal alterations involve sections of DNA<\/strong> either being deleted, duplicated, inverted, translocated<\/strong> (from one region of the chromosome to another), or inserted<\/strong> (added).\r\n\r\n \r\n\r\nThink about questions:\r\n\r\nAre most cancers caused by sporadic (spontaneous) or acquired mutations?\r\n\r\nAre most cancer caused by inherited mutations?","rendered":"

DNA Transcription and Translation<\/strong><\/h3>\n

It is often said that DNA<\/strong> contains the blueprint for the cell as it used to construct enzymes and proteins required for enabling and facilitating cellular reactions, cellular signalling, as well as building cellular components.\u00a0 There are 23 pairs of chromosomes<\/strong> in the human genome containing over 20,000 genes<\/strong> altogether, which are used to code for proteins and peptides.\u00a0 In brief, DNA transcription<\/strong> and translation<\/strong> involves the process of converting genetic information first from DNA into mRNA and then into functional proteins<\/strong>.\u00a0 \u00a0Transcription is the process in which a gene is copied into a complimentary strand of messenger RNA<\/strong> (mRNA).\u00a0 T<\/span>ranslation involves the mRNA sequence of nucleotides being used to string specific amino acids together to form proteins.<\/strong>\u00a0 In this section we will examine how mutations<\/strong> in DNA can affect the proteins being produced.\u00a0 \u00a0<\/span><\/p>\n

 <\/p>\n

The Effects of DNA Mutation on Protein Production<\/strong><\/h3>\n

As mentioned in the previous section, mutations<\/strong> in genes can occur due to various factors such as viruses, asbestos, radiation, cigarette smoke,<\/strong> or spontaneous errors during DNA duplication<\/strong>.\u00a0 There are several types of mutations that can occur on a strand of DNA and some can have significant effects, while other may not have any effect at all.<\/p>\n

In examining the effects of DNA mutations, we need to remember that genes<\/strong> are spread along chromosomes separated by sequences of non-coding regions<\/strong>.\u00a0 These non-coding regions don’t code for peptides or proteins, but can play other roles.\u00a0 For example, non-coding regions contain promotor regions<\/strong> that influence the rate of transcription<\/strong> of downstream genes.\u00a0 Some non-coding DNA is used to make non-coding RNA<\/strong> such as transfer RNA (tRNA)<\/strong> and ribosomal RNA (rRNA)<\/strong> molecules.\u00a0 \u00a0There are other non-coding regions that don’t appear to have any function at all and is referred to as “junk DNA”<\/strong>, though that is currently under investigation as non-coding DNA makes up over 98% of our genome and may be found to have important roles within the cell.\u00a0 One theory is that over the millennia, “junk DNA” has accumulated that may originally have had useful purposes, but are no longer required.\u00a0 It may too be that junk DNA has been perpetually inserted into the genome over time and been passed from one generation to the other.\u00a0 Some of this junk DNA likely came has from pre-historic viruses and bacteria.<\/p>\n

 <\/p>\n

Point Mutations and Frameshift Mutations and Cancer<\/strong><\/h3>\n

There are 3 types of mutations include insertion, substitution,<\/strong> and deletion<\/strong> mutations.\u00a0 Point mutations<\/strong> are the most common type of mutation and involve a substitution of a single nucleotide in DNA.\u00a0 A substitution mutation replaces one nucleotide with another (e.g. CAG to CAT), potentially altering one amino acid in the protein though not always.\u00a0 There are 3 possible outcomes.\u00a0 A point mutation can create a silent, missense<\/strong> or nonsense<\/strong> mutation as shown in the table below.<\/p>\n\n\n\n\n\n\n
Examples of Types of Point Mutation<\/strong><\/td>\nDNA Triplet \u2192 Mutated DNA Triplet<\/strong><\/td>\nEffect of Amino Acid Codon Sequence on Translated Protein<\/strong><\/td>\nCellular Effect<\/strong><\/td>\n<\/tr>\n
Silent Mutation<\/strong><\/td>\nACA \u2192 ACG<\/td>\nCysteine \u2192 Cysteine<\/td>\nnone<\/td>\n<\/tr>\n
Missense Mutation<\/strong><\/td>\nACA \u2192 ACC<\/span><\/td>\nCysteine \u2192 Tryptophan<\/td>\nmild to serious<\/td>\n<\/tr>\n
Nonsense Mutation<\/strong><\/td>\nACA \u2192 ACT<\/span><\/td>\nCysteine \u2192 Stop<\/td>\nserious<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n

The table above gives examples of point mutations that are classified as silent, missense and nonsense depending on the effect on the protein produced.\u00a0 A silent mutation<\/strong> occurs when the nucleotide substitution does not change the amino acid that is coded for and is therefore sometimes called a synonymous<\/strong> mutation.\u00a0 A missense<\/strong> mutation results in a new amino acid being coded for and its effects depend on whether the new amino acid changes the function of the protein or enzyme.\u00a0 There be no effect on the protein\/enzyme’s ability to function.\u00a0 However, there may be a loss of function or even a change of function that actively impedes cellular abilities or structure.\u00a0 Nonsense<\/strong> mutations result in a protein or enzyme that is either not functional or actively dysfunctional.\u00a0 In this case, unless the cell produces other similar proteins or enzymes that are able to compensate for this loss, the cell itself could become less functional, function inappropriately, or even die.\u00a0 Due to the difference created in the final peptide sequence, both missense and nonsense mutations are considered nonsynonymous<\/strong> mutations.<\/p>\n

Frameshift mutations<\/strong> occur when a nucleotide is either inserted<\/strong> or deleted<\/strong> within a gene’s coding region.\u00a0 As a result, there is a shift in the reading frame affecting the mRNA sequence that is transcribed and then translated.\u00a0 As a result of a frameshift, all of the DNA’s reading frames downstream of the mutation will be affected, potentially resulting in every subsequent codon as being different and coding for a different amino acid.<\/p>\n\n\n\n\n\n\n
Examples of Frameshift Mutations<\/strong><\/td>\nDNA Triplet Sequence<\/strong><\/td>\nmRNA Codon Sequence<\/strong><\/td>\nAmino Acid Sequence<\/strong><\/td>\n<\/tr>\n
Original Sequence<\/strong><\/td>\nTAC-CTA-TCT-ACC-A<\/td>\nAUG-GAU-AGA-UGG-U<\/td>\nMet-Asp-Arg-Trp<\/td>\n<\/tr>\n
Sequence with Insertion<\/strong><\/td>\nTAC-CTT<\/span>-ATC-TAC-C<\/td>\nAUG-GAA-UAG-AUG-G<\/td>\nMet-Glu-Stop<\/td>\n<\/tr>\n
Sequence with Deletion<\/strong><\/td>\nTAC-CTT-CTA-CCU<\/td>\nAUG-GAA-GAU-GGA<\/td>\nMet-Glu-Asp-Gly<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n

In the above examples of point mutations and frameshift mutations, it is evident the substitution, insertion or deletion of an amino acid within the coding region can lead to loss of a functional protein or enzyme.\u00a0 In the case of cancer,<\/strong> over 290 gene mutations have been identified which affect the function of key enzymes – most often those involved in regulating the rates of cell cycling, differentiation and apoptosis.<\/p>\n

Chromosomal Alterations<\/strong><\/h3>\n

Chromosomal alterations<\/strong> often result in death of the cell or organism (depending on the stage of development in which it occurs<\/em>) rather than resulting in cancer. Chromosomal alterations involve sections of DNA<\/strong> either being deleted, duplicated, inverted, translocated<\/strong> (from one region of the chromosome to another), or inserted<\/strong> (added).<\/p>\n

 <\/p>\n

Think about questions:<\/p>\n

Are most cancers caused by sporadic (spontaneous) or acquired mutations?<\/p>\n

Are most cancer caused by inherited mutations?<\/p>\n","protected":false},"author":1370,"menu_order":6,"template":"","meta":{"pb_show_title":"on","pb_short_title":"","pb_subtitle":"Pictures coming soon!","pb_authors":["zoe-soon"],"pb_section_license":"cc-by-nc-sa"},"chapter-type":[],"contributor":[60],"license":[57],"class_list":["post-1095","chapter","type-chapter","status-web-only","hentry","contributor-zoe-soon","license-cc-by-nc-sa"],"part":35,"_links":{"self":[{"href":"https:\/\/pressbooks.bccampus.ca\/pathophysiology\/wp-json\/pressbooks\/v2\/chapters\/1095","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/pressbooks.bccampus.ca\/pathophysiology\/wp-json\/pressbooks\/v2\/chapters"}],"about":[{"href":"https:\/\/pressbooks.bccampus.ca\/pathophysiology\/wp-json\/wp\/v2\/types\/chapter"}],"author":[{"embeddable":true,"href":"https:\/\/pressbooks.bccampus.ca\/pathophysiology\/wp-json\/wp\/v2\/users\/1370"}],"version-history":[{"count":21,"href":"https:\/\/pressbooks.bccampus.ca\/pathophysiology\/wp-json\/pressbooks\/v2\/chapters\/1095\/revisions"}],"predecessor-version":[{"id":4415,"href":"https:\/\/pressbooks.bccampus.ca\/pathophysiology\/wp-json\/pressbooks\/v2\/chapters\/1095\/revisions\/4415"}],"part":[{"href":"https:\/\/pressbooks.bccampus.ca\/pathophysiology\/wp-json\/pressbooks\/v2\/parts\/35"}],"metadata":[{"href":"https:\/\/pressbooks.bccampus.ca\/pathophysiology\/wp-json\/pressbooks\/v2\/chapters\/1095\/metadata\/"}],"wp:attachment":[{"href":"https:\/\/pressbooks.bccampus.ca\/pathophysiology\/wp-json\/wp\/v2\/media?parent=1095"}],"wp:term":[{"taxonomy":"chapter-type","embeddable":true,"href":"https:\/\/pressbooks.bccampus.ca\/pathophysiology\/wp-json\/pressbooks\/v2\/chapter-type?post=1095"},{"taxonomy":"contributor","embeddable":true,"href":"https:\/\/pressbooks.bccampus.ca\/pathophysiology\/wp-json\/wp\/v2\/contributor?post=1095"},{"taxonomy":"license","embeddable":true,"href":"https:\/\/pressbooks.bccampus.ca\/pathophysiology\/wp-json\/wp\/v2\/license?post=1095"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}