Transcription<\/h1>\r\n<\/div>\r\nTranscription<\/strong>\u00a0is the first part of the\u00a0central dogma\u00a0of molecular biology:\u00a0DNA<\/strong>\u00a0<\/strong>\u2192<\/strong>\u00a0<\/strong>RNA<\/strong>. It is the transfer of genetic instructions in DNA to mRNA. During transcription, a strand of mRNA is made to complement a strand of DNA. You can see how this happens in Figure 5.7.2.\r\n\r\n[caption id=\"attachment_2243\" align=\"aligncenter\" width=\"601\"]![\"\"](\"https:\/\/pressbooks.ccconline.org\/acchumanbio\/wp-content\/uploads\/sites\/152\/2023\/10\/Transcription-2.png\")
Figure 5.7.2 Transcription uses the sequence of bases in a strand of DNA to make a complementary strand of mRNA. Triplets are groups of three successive nucleotide bases in DNA. Codons are complementary groups of bases in mRNA.<\/em>[\/caption]\r\n<\/h2>\r\nTranscription begins when the enzyme RNA polymerase binds to a region of a gene called the promoter sequence. This signals the DNA to unwind so the enzyme can \u201cread\u201d the bases of DNA.\u00a0 The two strands of DNA are named based on whether they will be used as a template for RNA or not.\u00a0 The strand that is used as a template is called the template strand, or can also be called the a<\/span><\/span>ntisense<\/span>\u00a0strand.\u00a0 The sequence of bases on the opposite strand of DNA is called the non-coding or sense strand.\u00a0<\/span><\/span> Once the DNA has opened, and RNA polymerase has attached, the RNA polymerase moves along the DNA, adding RNA <\/span>nucleotides to the growing mRNA strand.\u00a0 The template strand of DNA is used as to create mRNA through complementary base pairing. Once the<\/span> mRNA strand is complete, and it detaches from DNA. The result is\u00a0 a strand of mRNA that is nearly identical to the coding strand DNA - the only difference being that DNA uses the base thymine, and the mRNA uses uracil in the place of thymine<\/span>\r\nProcessing mRNA<\/h2>\r\nIn [pb_glossary id=\"1573\"]eukaryotes[\/pb_glossary], the new [pb_glossary id=\"2212\"]mRNA[\/pb_glossary] is not yet ready for translation. At this stage, it is called pre-mRNA, and it must go through more processing before it leaves the\u00a0nucleus\u00a0as mature mRNA. The processing may include splicing, editing, and polyadenylation. These processes modify the mRNA in various ways. Such modifications allow a single gene to be used to make more than one\u00a0protein.\r\n\r\n \t- Splicing <\/strong>removes introns from mRNA, as shown in Figure 5.7.3. Introns<\/strong>\u00a0are regions that do not code for the protein. The remaining mRNA consists only of regions called\u00a0exons<\/strong>\u00a0that do code for the protein. The ribonucleoproteins in the diagram are small\u00a0proteins\u00a0in the nucleus that contain RNA and are needed for the splicing process.<\/li>\r\n \t
- Editing <\/strong>changes some of the nucleotides in mRNA. For example, a human protein called APOB, which helps transport\u00a0lipids\u00a0in the\u00a0blood, has two different forms because of editing. One form is smaller than the other because editing adds an earlier stop signal in mRNA.<\/li>\r\n \t
- 5' Capping\u00a0<\/strong>adds a methylated cap to the \"head\" of the mRNA.\u00a0 This cap protects the mRNA from breaking down, and helps the ribosomes know where to bind to the mRNA<\/li>\r\n \t
- [pb_glossary id=\"5946\"]Polyadenylation[\/pb_glossary] <\/strong>adds a \u201ctail\u201d to the mRNA. The tail consists of a string of As (adenine bases). It signals the end of mRNA. It is also involved in exporting mRNA from the nucleus, and it protects mRNA from\u00a0enzymes that might break it down.<\/li>\r\n<\/ul>\r\n\r\n\r\n[caption id=\"attachment_2370\" align=\"aligncenter\" width=\"754\"]
![\"mRNA](\"https:\/\/pressbooks.ccconline.org\/acchumanbio\/wp-content\/uploads\/sites\/152\/2023\/10\/Pre-mRNA-processing-1-2.png\")
Figure 5.7.3 Pre mRNA processing. mRNA requires processing before it leaves the nucleus.<\/em>[\/caption]\r\n\r\n<\/div>\r\n\r\nTranslation<\/h1>\r\n<\/div>\r\nTranslation<\/strong>\u00a0is the second part of the\u00a0central dogma\u00a0of molecular biology:\u00a0RNA <\/strong>\u2192<\/strong> Protein<\/strong>. It is the process in which the genetic code in [pb_glossary id=\"2212\"]mRNA[\/pb_glossary] is read to make a [pb_glossary id=\"5813\"]protein[\/pb_glossary]. Translation is illustrated in Figure 5.7.4. After mRNA leaves the [pb_glossary id=\"5797\"]nucleus[\/pb_glossary], it moves to a [pb_glossary id=\"5551\"]ribosome[\/pb_glossary], which consists of rRNA and proteins. The ribosome reads the sequence of [pb_glossary id=\"5945\"]codons[\/pb_glossary] in mRNA, and molecules of [pb_glossary id=\"2215\"]tRNA[\/pb_glossary] bring [pb_glossary id=\"5707\"]amino acids[\/pb_glossary] to the ribosome in the correct sequence.\r\n\r\nTranslation occurs in three stages: Initiation, Elongation and Termination.\r\n\r\nInitiation:<\/strong>\r\n\r\nAfter transcription in the nucleus, the mRNA exits through a nuclear pore and enters the cytoplasm.\u00a0 At the region on the mRNA containing the methylated cap and the start codon, the small and large subunits of the ribosome\u00a0 bind to the mRNA.\u00a0 These are then joined by a tRNA which contains the anticodons matching the start codon on the mRNA.\u00a0 This group of molecues (mRNA, ribosome, tRNA) is called an initiation complex.\r\n\r\nElongation:<\/strong>\r\n\r\ntRNA keep bringing amino acids to the growing polypeptide according to complementary base pairing between the codons on the mRNA and the anticodons on the tRNA.\u00a0 As a tRNA moves into the ribosome, its amino acid is transferred to the growing polypeptide.\u00a0 Once this transfer is complete, the tRNA leaves the ribosome, the ribosome moves one codon length down the mRNA, and a new tRNA enters with its corresponding amino acid.\u00a0 This process repeats and the polypeptide grows.\r\n\r\nTermination<\/b>:<\/strong>\r\n\r\nAt the end of the mRNA coding is a stop codon which will end the elongation stage.\u00a0 The stop codon doesn't call for a tRNA, but instead for a type of protein called a release factor, which will cause the entire complex (mRNA, ribosome, tRNA, and polypeptide) to break apart, releasing all of the components.\r\n\r\n \r\n\r\n \r\n\r\n\r\n[caption id=\"attachment_2374\" align=\"alignnone\" width=\"936\"]![\"\"](\"https:\/\/pressbooks.ccconline.org\/acchumanbio\/wp-content\/uploads\/sites\/152\/2023\/10\/Translation-2.jpg\")
Figure 5.7.4 Translation takes place in three stages: Initiation, Elongation and Termination.<\/em>[\/caption]\r\n\r\n<\/div>\r\nWatch this video \"Protein Synthesis (Updated) with the Amoeba Sisters\" to see this process in action:\r\n\r\nhttps:\/\/www.youtube.com\/watch?v=oefAI2x2CQM&t=3s\r\nProtein Synthesis (Updated), Amoeba Sisters, 2018.<\/p>\r\n\r\n
\r\nWhat Happens Next?<\/h1>\r\n<\/div>\r\nAfter a polypeptide chain is synthesized, it may undergo additional processes. For example, it may assume a folded shape due to interactions between its amino acids. It may also bind with other polypeptides or with different types of molecules, such as [pb_glossary id=\"5651\"]lipids[\/pb_glossary] or [pb_glossary id=\"5655\"]carbohydrates[\/pb_glossary]. Many proteins travel to the [pb_glossary id=\"5485\"]Golgi apparatus[\/pb_glossary] within the [pb_glossary id=\"5465\"]cytoplasm[\/pb_glossary] to be modified for the specific job they will do.7 Summary<\/span>\r\n\r\n5.7 Summary<\/h2>\r\n<\/header>\r\n\r\n\r\n \t- Protein synthesis is the process in which\u00a0cells\u00a0make proteins. It occurs in two stages: transcription and translation.<\/li>\r\n \t
- Transcription is the transfer of genetic instructions in DNA to mRNA in the nucleus. It includes three steps: initiation, elongation, and termination. After the mRNA is processed, it carries the instructions to a ribosome in the cytoplasm.<\/li>\r\n \t
- Translation occurs at the ribosome, which consists of rRNA and proteins. In translation, the instructions in mRNA are read, and tRNA brings the correct sequence of amino acids to the ribosome. Then, rRNA helps bonds form between the amino acids, producing a polypeptide chain.<\/li>\r\n \t
- After a polypeptide chain is synthesized, it may undergo additional processing to form the finished protein.<\/li>\r\n<\/ul>\r\n<\/div>\r\n<\/div>\r\n\r\n
\r\n5.7 Review Questions<\/span><\/h1>\r\n<\/header>\r\n\r\n\r\n \t- Relate protein synthesis and its two major phases to the central dogma of molecular biology.<\/li>\r\n \t
- Explain how mRNA is processed before it leaves the nucleus.<\/li>\r\n \t
- What additional processes might\u00a0a polypeptide chain undergo after it is synthesized?<\/li>\r\n \t
- Where does transcription take place in eukaryotes?<\/li>\r\n \t
- Where does translation take place?<\/li>\r\n \t
- [h5p id=\"501\"]<\/li>\r\n<\/ol>\r\n<\/div>\r\n<\/div>\r\n
\r\n5.7 Explore More<\/span><\/h1>\r\n<\/header>\r\n\r\n\r\nhttps:\/\/youtu.be\/2zAGAmTkZNY\r\nProtein Synthesis, Teacher's Pet, 2014.<\/p>\r\n\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n \r\n
Attributions<\/h2>\r\nFigure 5.7.1<\/strong>\r\n\r\nHow proteins are made<\/a> by Nicolle Rager, National Science Foundation<\/a> on Wikimedia Commons is released into the public domain<\/a> (https:\/\/en.wikipedia.org\/wiki\/Public_domain).<\/i>\r\n\r\nFigure 5.7.2<\/strong>\r\n\r\nTranscription<\/a> by National Human Genome Research Institute<\/a>, (reworked and vectorized by Sulai)<\/a> on Wikimedia Commons is released into the public domain<\/a> (https:\/\/en.wikipedia.org\/wiki\/Public_domain).<\/i>\r\n\r\nFigure 5.7.3<\/strong>\r\n\r\nPre mRNA processing by Christine Miller is used under a CC BY-NC-SA 4.0<\/a>\u00a0 (https:\/\/creativecommons.org\/licenses\/by-nc-sa\/4.0\/) license.\r\n\r\nFigure 5.7.4<\/strong>\r\n\r\nTranslation<\/a>\u00a0by CNX OpenStax<\/a> on Wikimedia Commons is used under a CC BY 4.0<\/a> (https:\/\/creativecommons.org\/licenses\/by\/4.0) license.\r\nReferences<\/h2>\r\n
Amoeba Sisters. (2018, January 18) Protein synthesis (Updated). YouTube. https:\/\/www.youtube.com\/watch?v=oefAI2x2CQM&feature=youtu.be<\/p>\r\n
Parker, N., Schneegurt, M., Thi Tu, A-H., Lister, P., Forster, B.M. (2016, November 1). Microbiology [online]. Figure 11.15 Translation in bacteria begins with the formation of the initiation complex. In Microbiology<\/em> (Section 11-4). OpenStax. https:\/\/openstax.org\/books\/microbiology\/pages\/11-4-protein-synthesis-translation<\/p>\r\nTeacher's Pet. (2014, December 7). Protein synthesis. YouTube. https:\/\/www.youtube.com\/watch?v=2zAGAmTkZNY&feature=youtu.be<\/p>","rendered":"
<\/p>\n![\"\"](\"https:\/\/pressbooks.ccconline.org\/acchumanbio\/wp-content\/uploads\/sites\/152\/2019\/06\/How-proteins-are-made-2.jpg\")
Figure 5.7.1 How proteins are made.<\/em><\/figcaption><\/figure>\nThe Art of Protein Synthesis<\/h1>\n
This amazing artwork (Figure 5.7.1) shows a process that takes place in the cells of all living things: the production of proteins. This process is called protein synthesis<\/a><\/strong>, and it\u00a0<\/strong>actually consists of two processes \u2014\u00a0transcription<\/a>\u00a0and translation<\/a>. In eukaryotic<\/a>\u00a0cells, transcription takes place in the\u00a0nucleus<\/a>. During transcription,\u00a0DNA<\/a>\u00a0is used as a template to make a molecule of messenger\u00a0RNA\u00a0(mRNA<\/a>). The molecule of mRNA then leaves the nucleus and goes to a\u00a0ribosome<\/a>\u00a0in the cytoplasm<\/a>, where translation occurs. During translation, the\u00a0genetic code in mRNA is read and used to make a polypeptide. These two processes are summed up by the\u00a0central dogma\u00a0of molecular biology:\u00a0DNA<\/a><\/strong>\u00a0<\/strong>\u2192<\/strong> RNA<\/a>\u00a0<\/strong>\u2192<\/strong>\u00a0<\/strong>Protein<\/a><\/strong>.<\/p>\n\nTranscription<\/h1>\n<\/div>\n
Transcription<\/strong>\u00a0is the first part of the\u00a0central dogma\u00a0of molecular biology:\u00a0DNA<\/strong>\u00a0<\/strong>\u2192<\/strong>\u00a0<\/strong>RNA<\/strong>. It is the transfer of genetic instructions in DNA to mRNA. During transcription, a strand of mRNA is made to complement a strand of DNA. You can see how this happens in Figure 5.7.2.<\/p>\nFigure 5.7.2 Transcription uses the sequence of bases in a strand of DNA to make a complementary strand of mRNA. Triplets are groups of three successive nucleotide bases in DNA. Codons are complementary groups of bases in mRNA.<\/em><\/figcaption><\/figure>\n<\/h2>\n
Transcription begins when the enzyme RNA polymerase binds to a region of a gene called the promoter sequence. This signals the DNA to unwind so the enzyme can \u201cread\u201d the bases of DNA.\u00a0 The two strands of DNA are named based on whether they will be used as a template for RNA or not.\u00a0 The strand that is used as a template is called the template strand, or can also be called the a<\/span><\/span>ntisense<\/span>\u00a0strand.\u00a0 The sequence of bases on the opposite strand of DNA is called the non-coding or sense strand.\u00a0<\/span><\/span> Once the DNA has opened, and RNA polymerase has attached, the RNA polymerase moves along the DNA, adding RNA <\/span>nucleotides to the growing mRNA strand.\u00a0 The template strand of DNA is used as to create mRNA through complementary base pairing. Once the<\/span> mRNA strand is complete, and it detaches from DNA. The result is\u00a0 a strand of mRNA that is nearly identical to the coding strand DNA – the only difference being that DNA uses the base thymine, and the mRNA uses uracil in the place of thymine<\/span><\/p>\nProcessing mRNA<\/h2>\n
In eukaryotes<\/a>, the new mRNA<\/a> is not yet ready for translation. At this stage, it is called pre-mRNA, and it must go through more processing before it leaves the\u00a0nucleus\u00a0as mature mRNA. The processing may include splicing, editing, and polyadenylation. These processes modify the mRNA in various ways. Such modifications allow a single gene to be used to make more than one\u00a0protein.<\/p>\n\n- Splicing <\/strong>removes introns from mRNA, as shown in Figure 5.7.3. Introns<\/strong>\u00a0are regions that do not code for the protein. The remaining mRNA consists only of regions called\u00a0exons<\/strong>\u00a0that do code for the protein. The ribonucleoproteins in the diagram are small\u00a0proteins\u00a0in the nucleus that contain RNA and are needed for the splicing process.<\/li>\n
- Editing <\/strong>changes some of the nucleotides in mRNA. For example, a human protein called APOB, which helps transport\u00a0lipids\u00a0in the\u00a0blood, has two different forms because of editing. One form is smaller than the other because editing adds an earlier stop signal in mRNA.<\/li>\n
- 5′ Capping\u00a0<\/strong>adds a methylated cap to the “head” of the mRNA.\u00a0 This cap protects the mRNA from breaking down, and helps the ribosomes know where to bind to the mRNA<\/li>\n
- Polyadenylation<\/a> <\/strong>adds a \u201ctail\u201d to the mRNA. The tail consists of a string of As (adenine bases). It signals the end of mRNA. It is also involved in exporting mRNA from the nucleus, and it protects mRNA from\u00a0enzymes that might break it down.<\/li>\n<\/ul>\n\n
Figure 5.7.3 Pre mRNA processing. mRNA requires processing before it leaves the nucleus.<\/em><\/figcaption><\/figure>\n<\/div>\n\nTranslation<\/h1>\n<\/div>\n
Translation<\/strong>\u00a0is the second part of the\u00a0central dogma\u00a0of molecular biology:\u00a0RNA <\/strong>\u2192<\/strong> Protein<\/strong>. It is the process in which the genetic code in mRNA<\/a> is read to make a protein<\/a>. Translation is illustrated in Figure 5.7.4. After mRNA leaves the nucleus<\/a>, it moves to a ribosome<\/a>, which consists of rRNA and proteins. The ribosome reads the sequence of codons<\/a> in mRNA, and molecules of tRNA<\/a> bring amino acids<\/a> to the ribosome in the correct sequence.<\/p>\nTranslation occurs in three stages: Initiation, Elongation and Termination.<\/p>\n
Initiation:<\/strong><\/p>\nAfter transcription in the nucleus, the mRNA exits through a nuclear pore and enters the cytoplasm.\u00a0 At the region on the mRNA containing the methylated cap and the start codon, the small and large subunits of the ribosome\u00a0 bind to the mRNA.\u00a0 These are then joined by a tRNA which contains the anticodons matching the start codon on the mRNA.\u00a0 This group of molecues (mRNA, ribosome, tRNA) is called an initiation complex.<\/p>\n
Elongation:<\/strong><\/p>\ntRNA keep bringing amino acids to the growing polypeptide according to complementary base pairing between the codons on the mRNA and the anticodons on the tRNA.\u00a0 As a tRNA moves into the ribosome, its amino acid is transferred to the growing polypeptide.\u00a0 Once this transfer is complete, the tRNA leaves the ribosome, the ribosome moves one codon length down the mRNA, and a new tRNA enters with its corresponding amino acid.\u00a0 This process repeats and the polypeptide grows.<\/p>\n
Termination<\/b>:<\/strong><\/p>\nAt the end of the mRNA coding is a stop codon which will end the elongation stage.\u00a0 The stop codon doesn’t call for a tRNA, but instead for a type of protein called a release factor, which will cause the entire complex (mRNA, ribosome, tRNA, and polypeptide) to break apart, releasing all of the components.<\/p>\n
<\/p>\n
<\/p>\n
\nFigure 5.7.4 Translation takes place in three stages: Initiation, Elongation and Termination.<\/em><\/figcaption><\/figure>\n<\/div>\nWatch this video “Protein Synthesis (Updated) with the Amoeba Sisters” to see this process in action:<\/p>\n
Processing mRNA<\/h2>\r\nIn [pb_glossary id=\"1573\"]eukaryotes[\/pb_glossary], the new [pb_glossary id=\"2212\"]mRNA[\/pb_glossary] is not yet ready for translation. At this stage, it is called pre-mRNA, and it must go through more processing before it leaves the\u00a0nucleus\u00a0as mature mRNA. The processing may include splicing, editing, and polyadenylation. These processes modify the mRNA in various ways. Such modifications allow a single gene to be used to make more than one\u00a0protein.\r\n\r\n \t- Splicing <\/strong>removes introns from mRNA, as shown in Figure 5.7.3. Introns<\/strong>\u00a0are regions that do not code for the protein. The remaining mRNA consists only of regions called\u00a0exons<\/strong>\u00a0that do code for the protein. The ribonucleoproteins in the diagram are small\u00a0proteins\u00a0in the nucleus that contain RNA and are needed for the splicing process.<\/li>\r\n \t
- Editing <\/strong>changes some of the nucleotides in mRNA. For example, a human protein called APOB, which helps transport\u00a0lipids\u00a0in the\u00a0blood, has two different forms because of editing. One form is smaller than the other because editing adds an earlier stop signal in mRNA.<\/li>\r\n \t
- 5' Capping\u00a0<\/strong>adds a methylated cap to the \"head\" of the mRNA.\u00a0 This cap protects the mRNA from breaking down, and helps the ribosomes know where to bind to the mRNA<\/li>\r\n \t
- [pb_glossary id=\"5946\"]Polyadenylation[\/pb_glossary] <\/strong>adds a \u201ctail\u201d to the mRNA. The tail consists of a string of As (adenine bases). It signals the end of mRNA. It is also involved in exporting mRNA from the nucleus, and it protects mRNA from\u00a0enzymes that might break it down.<\/li>\r\n<\/ul>\r\n\r\n\r\n[caption id=\"attachment_2370\" align=\"aligncenter\" width=\"754\"] Figure 5.7.3 Pre mRNA processing. mRNA requires processing before it leaves the nucleus.<\/em>[\/caption]\r\n\r\n<\/div>\r\n\r\n
Translation<\/h1>\r\n<\/div>\r\nTranslation<\/strong>\u00a0is the second part of the\u00a0central dogma\u00a0of molecular biology:\u00a0RNA <\/strong>\u2192<\/strong> Protein<\/strong>. It is the process in which the genetic code in [pb_glossary id=\"2212\"]mRNA[\/pb_glossary] is read to make a [pb_glossary id=\"5813\"]protein[\/pb_glossary]. Translation is illustrated in Figure 5.7.4. After mRNA leaves the [pb_glossary id=\"5797\"]nucleus[\/pb_glossary], it moves to a [pb_glossary id=\"5551\"]ribosome[\/pb_glossary], which consists of rRNA and proteins. The ribosome reads the sequence of [pb_glossary id=\"5945\"]codons[\/pb_glossary] in mRNA, and molecules of [pb_glossary id=\"2215\"]tRNA[\/pb_glossary] bring [pb_glossary id=\"5707\"]amino acids[\/pb_glossary] to the ribosome in the correct sequence.\r\n\r\nTranslation occurs in three stages: Initiation, Elongation and Termination.\r\n\r\nInitiation:<\/strong>\r\n\r\nAfter transcription in the nucleus, the mRNA exits through a nuclear pore and enters the cytoplasm.\u00a0 At the region on the mRNA containing the methylated cap and the start codon, the small and large subunits of the ribosome\u00a0 bind to the mRNA.\u00a0 These are then joined by a tRNA which contains the anticodons matching the start codon on the mRNA.\u00a0 This group of molecues (mRNA, ribosome, tRNA) is called an initiation complex.\r\n\r\nElongation:<\/strong>\r\n\r\ntRNA keep bringing amino acids to the growing polypeptide according to complementary base pairing between the codons on the mRNA and the anticodons on the tRNA.\u00a0 As a tRNA moves into the ribosome, its amino acid is transferred to the growing polypeptide.\u00a0 Once this transfer is complete, the tRNA leaves the ribosome, the ribosome moves one codon length down the mRNA, and a new tRNA enters with its corresponding amino acid.\u00a0 This process repeats and the polypeptide grows.\r\n\r\nTermination<\/b>:<\/strong>\r\n\r\nAt the end of the mRNA coding is a stop codon which will end the elongation stage.\u00a0 The stop codon doesn't call for a tRNA, but instead for a type of protein called a release factor, which will cause the entire complex (mRNA, ribosome, tRNA, and polypeptide) to break apart, releasing all of the components.\r\n\r\n \r\n\r\n \r\n\r\n\r\n[caption id=\"attachment_2374\" align=\"alignnone\" width=\"936\"] Figure 5.7.4 Translation takes place in three stages: Initiation, Elongation and Termination.<\/em>[\/caption]\r\n\r\n<\/div>\r\nWatch this video \"Protein Synthesis (Updated) with the Amoeba Sisters\" to see this process in action:\r\n\r\nhttps:\/\/www.youtube.com\/watch?v=oefAI2x2CQM&t=3s\r\nProtein Synthesis (Updated), Amoeba Sisters, 2018.<\/p>\r\n\r\n
\r\nWhat Happens Next?<\/h1>\r\n<\/div>\r\nAfter a polypeptide chain is synthesized, it may undergo additional processes. For example, it may assume a folded shape due to interactions between its amino acids. It may also bind with other polypeptides or with different types of molecules, such as [pb_glossary id=\"5651\"]lipids[\/pb_glossary] or [pb_glossary id=\"5655\"]carbohydrates[\/pb_glossary]. Many proteins travel to the [pb_glossary id=\"5485\"]Golgi apparatus[\/pb_glossary] within the [pb_glossary id=\"5465\"]cytoplasm[\/pb_glossary] to be modified for the specific job they will do.7 Summary<\/span>\r\n\r\n5.7 Summary<\/h2>\r\n<\/header>\r\n\r\n\r\n \t- Protein synthesis is the process in which\u00a0cells\u00a0make proteins. It occurs in two stages: transcription and translation.<\/li>\r\n \t
- Transcription is the transfer of genetic instructions in DNA to mRNA in the nucleus. It includes three steps: initiation, elongation, and termination. After the mRNA is processed, it carries the instructions to a ribosome in the cytoplasm.<\/li>\r\n \t
- Translation occurs at the ribosome, which consists of rRNA and proteins. In translation, the instructions in mRNA are read, and tRNA brings the correct sequence of amino acids to the ribosome. Then, rRNA helps bonds form between the amino acids, producing a polypeptide chain.<\/li>\r\n \t
- After a polypeptide chain is synthesized, it may undergo additional processing to form the finished protein.<\/li>\r\n<\/ul>\r\n<\/div>\r\n<\/div>\r\n\r\n
\r\n5.7 Review Questions<\/span><\/h1>\r\n<\/header>\r\n\r\n\r\n \t- Relate protein synthesis and its two major phases to the central dogma of molecular biology.<\/li>\r\n \t
- Explain how mRNA is processed before it leaves the nucleus.<\/li>\r\n \t
- What additional processes might\u00a0a polypeptide chain undergo after it is synthesized?<\/li>\r\n \t
- Where does transcription take place in eukaryotes?<\/li>\r\n \t
- Where does translation take place?<\/li>\r\n \t
- [h5p id=\"501\"]<\/li>\r\n<\/ol>\r\n<\/div>\r\n<\/div>\r\n
\r\n5.7 Explore More<\/span><\/h1>\r\n<\/header>\r\n\r\n\r\nhttps:\/\/youtu.be\/2zAGAmTkZNY\r\nProtein Synthesis, Teacher's Pet, 2014.<\/p>\r\n\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n \r\n
Attributions<\/h2>\r\nFigure 5.7.1<\/strong>\r\n\r\nHow proteins are made<\/a> by Nicolle Rager, National Science Foundation<\/a> on Wikimedia Commons is released into the public domain<\/a> (https:\/\/en.wikipedia.org\/wiki\/Public_domain).<\/i>\r\n\r\nFigure 5.7.2<\/strong>\r\n\r\nTranscription<\/a> by National Human Genome Research Institute<\/a>, (reworked and vectorized by Sulai)<\/a> on Wikimedia Commons is released into the public domain<\/a> (https:\/\/en.wikipedia.org\/wiki\/Public_domain).<\/i>\r\n\r\nFigure 5.7.3<\/strong>\r\n\r\nPre mRNA processing by Christine Miller is used under a CC BY-NC-SA 4.0<\/a>\u00a0 (https:\/\/creativecommons.org\/licenses\/by-nc-sa\/4.0\/) license.\r\n\r\nFigure 5.7.4<\/strong>\r\n\r\nTranslation<\/a>\u00a0by CNX OpenStax<\/a> on Wikimedia Commons is used under a CC BY 4.0<\/a> (https:\/\/creativecommons.org\/licenses\/by\/4.0) license.\r\nReferences<\/h2>\r\n
Amoeba Sisters. (2018, January 18) Protein synthesis (Updated). YouTube. https:\/\/www.youtube.com\/watch?v=oefAI2x2CQM&feature=youtu.be<\/p>\r\n
Parker, N., Schneegurt, M., Thi Tu, A-H., Lister, P., Forster, B.M. (2016, November 1). Microbiology [online]. Figure 11.15 Translation in bacteria begins with the formation of the initiation complex. In Microbiology<\/em> (Section 11-4). OpenStax. https:\/\/openstax.org\/books\/microbiology\/pages\/11-4-protein-synthesis-translation<\/p>\r\nTeacher's Pet. (2014, December 7). Protein synthesis. YouTube. https:\/\/www.youtube.com\/watch?v=2zAGAmTkZNY&feature=youtu.be<\/p>","rendered":"
<\/p>\nFigure 5.7.1 How proteins are made.<\/em><\/figcaption><\/figure>\nThe Art of Protein Synthesis<\/h1>\n
This amazing artwork (Figure 5.7.1) shows a process that takes place in the cells of all living things: the production of proteins. This process is called protein synthesis<\/a><\/strong>, and it\u00a0<\/strong>actually consists of two processes \u2014\u00a0transcription<\/a>\u00a0and translation<\/a>. In eukaryotic<\/a>\u00a0cells, transcription takes place in the\u00a0nucleus<\/a>. During transcription,\u00a0DNA<\/a>\u00a0is used as a template to make a molecule of messenger\u00a0RNA\u00a0(mRNA<\/a>). The molecule of mRNA then leaves the nucleus and goes to a\u00a0ribosome<\/a>\u00a0in the cytoplasm<\/a>, where translation occurs. During translation, the\u00a0genetic code in mRNA is read and used to make a polypeptide. These two processes are summed up by the\u00a0central dogma\u00a0of molecular biology:\u00a0DNA<\/a><\/strong>\u00a0<\/strong>\u2192<\/strong> RNA<\/a>\u00a0<\/strong>\u2192<\/strong>\u00a0<\/strong>Protein<\/a><\/strong>.<\/p>\n\nTranscription<\/h1>\n<\/div>\n
Transcription<\/strong>\u00a0is the first part of the\u00a0central dogma\u00a0of molecular biology:\u00a0DNA<\/strong>\u00a0<\/strong>\u2192<\/strong>\u00a0<\/strong>RNA<\/strong>. It is the transfer of genetic instructions in DNA to mRNA. During transcription, a strand of mRNA is made to complement a strand of DNA. You can see how this happens in Figure 5.7.2.<\/p>\nFigure 5.7.2 Transcription uses the sequence of bases in a strand of DNA to make a complementary strand of mRNA. Triplets are groups of three successive nucleotide bases in DNA. Codons are complementary groups of bases in mRNA.<\/em><\/figcaption><\/figure>\n<\/h2>\n
Transcription begins when the enzyme RNA polymerase binds to a region of a gene called the promoter sequence. This signals the DNA to unwind so the enzyme can \u201cread\u201d the bases of DNA.\u00a0 The two strands of DNA are named based on whether they will be used as a template for RNA or not.\u00a0 The strand that is used as a template is called the template strand, or can also be called the a<\/span><\/span>ntisense<\/span>\u00a0strand.\u00a0 The sequence of bases on the opposite strand of DNA is called the non-coding or sense strand.\u00a0<\/span><\/span> Once the DNA has opened, and RNA polymerase has attached, the RNA polymerase moves along the DNA, adding RNA <\/span>nucleotides to the growing mRNA strand.\u00a0 The template strand of DNA is used as to create mRNA through complementary base pairing. Once the<\/span> mRNA strand is complete, and it detaches from DNA. The result is\u00a0 a strand of mRNA that is nearly identical to the coding strand DNA – the only difference being that DNA uses the base thymine, and the mRNA uses uracil in the place of thymine<\/span><\/p>\nProcessing mRNA<\/h2>\n
In eukaryotes<\/a>, the new mRNA<\/a> is not yet ready for translation. At this stage, it is called pre-mRNA, and it must go through more processing before it leaves the\u00a0nucleus\u00a0as mature mRNA. The processing may include splicing, editing, and polyadenylation. These processes modify the mRNA in various ways. Such modifications allow a single gene to be used to make more than one\u00a0protein.<\/p>\n\n- Splicing <\/strong>removes introns from mRNA, as shown in Figure 5.7.3. Introns<\/strong>\u00a0are regions that do not code for the protein. The remaining mRNA consists only of regions called\u00a0exons<\/strong>\u00a0that do code for the protein. The ribonucleoproteins in the diagram are small\u00a0proteins\u00a0in the nucleus that contain RNA and are needed for the splicing process.<\/li>\n
- Editing <\/strong>changes some of the nucleotides in mRNA. For example, a human protein called APOB, which helps transport\u00a0lipids\u00a0in the\u00a0blood, has two different forms because of editing. One form is smaller than the other because editing adds an earlier stop signal in mRNA.<\/li>\n
- 5′ Capping\u00a0<\/strong>adds a methylated cap to the “head” of the mRNA.\u00a0 This cap protects the mRNA from breaking down, and helps the ribosomes know where to bind to the mRNA<\/li>\n
- Polyadenylation<\/a> <\/strong>adds a \u201ctail\u201d to the mRNA. The tail consists of a string of As (adenine bases). It signals the end of mRNA. It is also involved in exporting mRNA from the nucleus, and it protects mRNA from\u00a0enzymes that might break it down.<\/li>\n<\/ul>\n\n
Figure 5.7.3 Pre mRNA processing. mRNA requires processing before it leaves the nucleus.<\/em><\/figcaption><\/figure>\n<\/div>\n\nTranslation<\/h1>\n<\/div>\n
Translation<\/strong>\u00a0is the second part of the\u00a0central dogma\u00a0of molecular biology:\u00a0RNA <\/strong>\u2192<\/strong> Protein<\/strong>. It is the process in which the genetic code in mRNA<\/a> is read to make a protein<\/a>. Translation is illustrated in Figure 5.7.4. After mRNA leaves the nucleus<\/a>, it moves to a ribosome<\/a>, which consists of rRNA and proteins. The ribosome reads the sequence of codons<\/a> in mRNA, and molecules of tRNA<\/a> bring amino acids<\/a> to the ribosome in the correct sequence.<\/p>\nTranslation occurs in three stages: Initiation, Elongation and Termination.<\/p>\n
Initiation:<\/strong><\/p>\nAfter transcription in the nucleus, the mRNA exits through a nuclear pore and enters the cytoplasm.\u00a0 At the region on the mRNA containing the methylated cap and the start codon, the small and large subunits of the ribosome\u00a0 bind to the mRNA.\u00a0 These are then joined by a tRNA which contains the anticodons matching the start codon on the mRNA.\u00a0 This group of molecues (mRNA, ribosome, tRNA) is called an initiation complex.<\/p>\n
Elongation:<\/strong><\/p>\ntRNA keep bringing amino acids to the growing polypeptide according to complementary base pairing between the codons on the mRNA and the anticodons on the tRNA.\u00a0 As a tRNA moves into the ribosome, its amino acid is transferred to the growing polypeptide.\u00a0 Once this transfer is complete, the tRNA leaves the ribosome, the ribosome moves one codon length down the mRNA, and a new tRNA enters with its corresponding amino acid.\u00a0 This process repeats and the polypeptide grows.<\/p>\n
Termination<\/b>:<\/strong><\/p>\nAt the end of the mRNA coding is a stop codon which will end the elongation stage.\u00a0 The stop codon doesn’t call for a tRNA, but instead for a type of protein called a release factor, which will cause the entire complex (mRNA, ribosome, tRNA, and polypeptide) to break apart, releasing all of the components.<\/p>\n
<\/p>\n
<\/p>\n
\nFigure 5.7.4 Translation takes place in three stages: Initiation, Elongation and Termination.<\/em><\/figcaption><\/figure>\n<\/div>\nWatch this video “Protein Synthesis (Updated) with the Amoeba Sisters” to see this process in action:<\/p>\n
Figure 5.7.3 Pre mRNA processing. mRNA requires processing before it leaves the nucleus.<\/em>[\/caption]\r\n\r\n<\/div>\r\nTranslation<\/h1>\r\n<\/div>\r\nTranslation<\/strong>\u00a0is the second part of the\u00a0central dogma\u00a0of molecular biology:\u00a0RNA <\/strong>\u2192<\/strong> Protein<\/strong>. It is the process in which the genetic code in [pb_glossary id=\"2212\"]mRNA[\/pb_glossary] is read to make a [pb_glossary id=\"5813\"]protein[\/pb_glossary]. Translation is illustrated in Figure 5.7.4. After mRNA leaves the [pb_glossary id=\"5797\"]nucleus[\/pb_glossary], it moves to a [pb_glossary id=\"5551\"]ribosome[\/pb_glossary], which consists of rRNA and proteins. The ribosome reads the sequence of [pb_glossary id=\"5945\"]codons[\/pb_glossary] in mRNA, and molecules of [pb_glossary id=\"2215\"]tRNA[\/pb_glossary] bring [pb_glossary id=\"5707\"]amino acids[\/pb_glossary] to the ribosome in the correct sequence.\r\n\r\nTranslation occurs in three stages: Initiation, Elongation and Termination.\r\n\r\nInitiation:<\/strong>\r\n\r\nAfter transcription in the nucleus, the mRNA exits through a nuclear pore and enters the cytoplasm.\u00a0 At the region on the mRNA containing the methylated cap and the start codon, the small and large subunits of the ribosome\u00a0 bind to the mRNA.\u00a0 These are then joined by a tRNA which contains the anticodons matching the start codon on the mRNA.\u00a0 This group of molecues (mRNA, ribosome, tRNA) is called an initiation complex.\r\n\r\nElongation:<\/strong>\r\n\r\ntRNA keep bringing amino acids to the growing polypeptide according to complementary base pairing between the codons on the mRNA and the anticodons on the tRNA.\u00a0 As a tRNA moves into the ribosome, its amino acid is transferred to the growing polypeptide.\u00a0 Once this transfer is complete, the tRNA leaves the ribosome, the ribosome moves one codon length down the mRNA, and a new tRNA enters with its corresponding amino acid.\u00a0 This process repeats and the polypeptide grows.\r\n\r\nTermination<\/b>:<\/strong>\r\n\r\nAt the end of the mRNA coding is a stop codon which will end the elongation stage.\u00a0 The stop codon doesn't call for a tRNA, but instead for a type of protein called a release factor, which will cause the entire complex (mRNA, ribosome, tRNA, and polypeptide) to break apart, releasing all of the components.\r\n\r\n \r\n\r\n \r\n\r\n\r\n[caption id=\"attachment_2374\" align=\"alignnone\" width=\"936\"] Figure 5.7.4 Translation takes place in three stages: Initiation, Elongation and Termination.<\/em>[\/caption]\r\n\r\n<\/div>\r\nWatch this video \"Protein Synthesis (Updated) with the Amoeba Sisters\" to see this process in action:\r\n\r\nhttps:\/\/www.youtube.com\/watch?v=oefAI2x2CQM&t=3s\r\nProtein Synthesis (Updated), Amoeba Sisters, 2018.<\/p>\r\n\r\n
\r\nWhat Happens Next?<\/h1>\r\n<\/div>\r\nAfter a polypeptide chain is synthesized, it may undergo additional processes. For example, it may assume a folded shape due to interactions between its amino acids. It may also bind with other polypeptides or with different types of molecules, such as [pb_glossary id=\"5651\"]lipids[\/pb_glossary] or [pb_glossary id=\"5655\"]carbohydrates[\/pb_glossary]. Many proteins travel to the [pb_glossary id=\"5485\"]Golgi apparatus[\/pb_glossary] within the [pb_glossary id=\"5465\"]cytoplasm[\/pb_glossary] to be modified for the specific job they will do.7 Summary<\/span>\r\n\r\n5.7 Summary<\/h2>\r\n<\/header>\r\n\r\n\r\n \t- Protein synthesis is the process in which\u00a0cells\u00a0make proteins. It occurs in two stages: transcription and translation.<\/li>\r\n \t
- Transcription is the transfer of genetic instructions in DNA to mRNA in the nucleus. It includes three steps: initiation, elongation, and termination. After the mRNA is processed, it carries the instructions to a ribosome in the cytoplasm.<\/li>\r\n \t
- Translation occurs at the ribosome, which consists of rRNA and proteins. In translation, the instructions in mRNA are read, and tRNA brings the correct sequence of amino acids to the ribosome. Then, rRNA helps bonds form between the amino acids, producing a polypeptide chain.<\/li>\r\n \t
- After a polypeptide chain is synthesized, it may undergo additional processing to form the finished protein.<\/li>\r\n<\/ul>\r\n<\/div>\r\n<\/div>\r\n\r\n
\r\n5.7 Review Questions<\/span><\/h1>\r\n<\/header>\r\n\r\n\r\n \t- Relate protein synthesis and its two major phases to the central dogma of molecular biology.<\/li>\r\n \t
- Explain how mRNA is processed before it leaves the nucleus.<\/li>\r\n \t
- What additional processes might\u00a0a polypeptide chain undergo after it is synthesized?<\/li>\r\n \t
- Where does transcription take place in eukaryotes?<\/li>\r\n \t
- Where does translation take place?<\/li>\r\n \t
- [h5p id=\"501\"]<\/li>\r\n<\/ol>\r\n<\/div>\r\n<\/div>\r\n
\r\n5.7 Explore More<\/span><\/h1>\r\n<\/header>\r\n\r\n\r\nhttps:\/\/youtu.be\/2zAGAmTkZNY\r\nProtein Synthesis, Teacher's Pet, 2014.<\/p>\r\n\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n \r\n
Attributions<\/h2>\r\nFigure 5.7.1<\/strong>\r\n\r\nHow proteins are made<\/a> by Nicolle Rager, National Science Foundation<\/a> on Wikimedia Commons is released into the public domain<\/a> (https:\/\/en.wikipedia.org\/wiki\/Public_domain).<\/i>\r\n\r\nFigure 5.7.2<\/strong>\r\n\r\nTranscription<\/a> by National Human Genome Research Institute<\/a>, (reworked and vectorized by Sulai)<\/a> on Wikimedia Commons is released into the public domain<\/a> (https:\/\/en.wikipedia.org\/wiki\/Public_domain).<\/i>\r\n\r\nFigure 5.7.3<\/strong>\r\n\r\nPre mRNA processing by Christine Miller is used under a CC BY-NC-SA 4.0<\/a>\u00a0 (https:\/\/creativecommons.org\/licenses\/by-nc-sa\/4.0\/) license.\r\n\r\nFigure 5.7.4<\/strong>\r\n\r\nTranslation<\/a>\u00a0by CNX OpenStax<\/a> on Wikimedia Commons is used under a CC BY 4.0<\/a> (https:\/\/creativecommons.org\/licenses\/by\/4.0) license.\r\nReferences<\/h2>\r\n
Amoeba Sisters. (2018, January 18) Protein synthesis (Updated). YouTube. https:\/\/www.youtube.com\/watch?v=oefAI2x2CQM&feature=youtu.be<\/p>\r\n
Parker, N., Schneegurt, M., Thi Tu, A-H., Lister, P., Forster, B.M. (2016, November 1). Microbiology [online]. Figure 11.15 Translation in bacteria begins with the formation of the initiation complex. In Microbiology<\/em> (Section 11-4). OpenStax. https:\/\/openstax.org\/books\/microbiology\/pages\/11-4-protein-synthesis-translation<\/p>\r\nTeacher's Pet. (2014, December 7). Protein synthesis. YouTube. https:\/\/www.youtube.com\/watch?v=2zAGAmTkZNY&feature=youtu.be<\/p>","rendered":"
<\/p>\nFigure 5.7.1 How proteins are made.<\/em><\/figcaption><\/figure>\nThe Art of Protein Synthesis<\/h1>\n
This amazing artwork (Figure 5.7.1) shows a process that takes place in the cells of all living things: the production of proteins. This process is called protein synthesis<\/a><\/strong>, and it\u00a0<\/strong>actually consists of two processes \u2014\u00a0transcription<\/a>\u00a0and translation<\/a>. In eukaryotic<\/a>\u00a0cells, transcription takes place in the\u00a0nucleus<\/a>. During transcription,\u00a0DNA<\/a>\u00a0is used as a template to make a molecule of messenger\u00a0RNA\u00a0(mRNA<\/a>). The molecule of mRNA then leaves the nucleus and goes to a\u00a0ribosome<\/a>\u00a0in the cytoplasm<\/a>, where translation occurs. During translation, the\u00a0genetic code in mRNA is read and used to make a polypeptide. These two processes are summed up by the\u00a0central dogma\u00a0of molecular biology:\u00a0DNA<\/a><\/strong>\u00a0<\/strong>\u2192<\/strong> RNA<\/a>\u00a0<\/strong>\u2192<\/strong>\u00a0<\/strong>Protein<\/a><\/strong>.<\/p>\n\nTranscription<\/h1>\n<\/div>\n
Transcription<\/strong>\u00a0is the first part of the\u00a0central dogma\u00a0of molecular biology:\u00a0DNA<\/strong>\u00a0<\/strong>\u2192<\/strong>\u00a0<\/strong>RNA<\/strong>. It is the transfer of genetic instructions in DNA to mRNA. During transcription, a strand of mRNA is made to complement a strand of DNA. You can see how this happens in Figure 5.7.2.<\/p>\nFigure 5.7.2 Transcription uses the sequence of bases in a strand of DNA to make a complementary strand of mRNA. Triplets are groups of three successive nucleotide bases in DNA. Codons are complementary groups of bases in mRNA.<\/em><\/figcaption><\/figure>\n<\/h2>\n
Transcription begins when the enzyme RNA polymerase binds to a region of a gene called the promoter sequence. This signals the DNA to unwind so the enzyme can \u201cread\u201d the bases of DNA.\u00a0 The two strands of DNA are named based on whether they will be used as a template for RNA or not.\u00a0 The strand that is used as a template is called the template strand, or can also be called the a<\/span><\/span>ntisense<\/span>\u00a0strand.\u00a0 The sequence of bases on the opposite strand of DNA is called the non-coding or sense strand.\u00a0<\/span><\/span> Once the DNA has opened, and RNA polymerase has attached, the RNA polymerase moves along the DNA, adding RNA <\/span>nucleotides to the growing mRNA strand.\u00a0 The template strand of DNA is used as to create mRNA through complementary base pairing. Once the<\/span> mRNA strand is complete, and it detaches from DNA. The result is\u00a0 a strand of mRNA that is nearly identical to the coding strand DNA – the only difference being that DNA uses the base thymine, and the mRNA uses uracil in the place of thymine<\/span><\/p>\nProcessing mRNA<\/h2>\n
In eukaryotes<\/a>, the new mRNA<\/a> is not yet ready for translation. At this stage, it is called pre-mRNA, and it must go through more processing before it leaves the\u00a0nucleus\u00a0as mature mRNA. The processing may include splicing, editing, and polyadenylation. These processes modify the mRNA in various ways. Such modifications allow a single gene to be used to make more than one\u00a0protein.<\/p>\n\n- Splicing <\/strong>removes introns from mRNA, as shown in Figure 5.7.3. Introns<\/strong>\u00a0are regions that do not code for the protein. The remaining mRNA consists only of regions called\u00a0exons<\/strong>\u00a0that do code for the protein. The ribonucleoproteins in the diagram are small\u00a0proteins\u00a0in the nucleus that contain RNA and are needed for the splicing process.<\/li>\n
- Editing <\/strong>changes some of the nucleotides in mRNA. For example, a human protein called APOB, which helps transport\u00a0lipids\u00a0in the\u00a0blood, has two different forms because of editing. One form is smaller than the other because editing adds an earlier stop signal in mRNA.<\/li>\n
- 5′ Capping\u00a0<\/strong>adds a methylated cap to the “head” of the mRNA.\u00a0 This cap protects the mRNA from breaking down, and helps the ribosomes know where to bind to the mRNA<\/li>\n
- Polyadenylation<\/a> <\/strong>adds a \u201ctail\u201d to the mRNA. The tail consists of a string of As (adenine bases). It signals the end of mRNA. It is also involved in exporting mRNA from the nucleus, and it protects mRNA from\u00a0enzymes that might break it down.<\/li>\n<\/ul>\n\n
Figure 5.7.3 Pre mRNA processing. mRNA requires processing before it leaves the nucleus.<\/em><\/figcaption><\/figure>\n<\/div>\n\nTranslation<\/h1>\n<\/div>\n
Translation<\/strong>\u00a0is the second part of the\u00a0central dogma\u00a0of molecular biology:\u00a0RNA <\/strong>\u2192<\/strong> Protein<\/strong>. It is the process in which the genetic code in mRNA<\/a> is read to make a protein<\/a>. Translation is illustrated in Figure 5.7.4. After mRNA leaves the nucleus<\/a>, it moves to a ribosome<\/a>, which consists of rRNA and proteins. The ribosome reads the sequence of codons<\/a> in mRNA, and molecules of tRNA<\/a> bring amino acids<\/a> to the ribosome in the correct sequence.<\/p>\nTranslation occurs in three stages: Initiation, Elongation and Termination.<\/p>\n
Initiation:<\/strong><\/p>\nAfter transcription in the nucleus, the mRNA exits through a nuclear pore and enters the cytoplasm.\u00a0 At the region on the mRNA containing the methylated cap and the start codon, the small and large subunits of the ribosome\u00a0 bind to the mRNA.\u00a0 These are then joined by a tRNA which contains the anticodons matching the start codon on the mRNA.\u00a0 This group of molecues (mRNA, ribosome, tRNA) is called an initiation complex.<\/p>\n
Elongation:<\/strong><\/p>\ntRNA keep bringing amino acids to the growing polypeptide according to complementary base pairing between the codons on the mRNA and the anticodons on the tRNA.\u00a0 As a tRNA moves into the ribosome, its amino acid is transferred to the growing polypeptide.\u00a0 Once this transfer is complete, the tRNA leaves the ribosome, the ribosome moves one codon length down the mRNA, and a new tRNA enters with its corresponding amino acid.\u00a0 This process repeats and the polypeptide grows.<\/p>\n
Termination<\/b>:<\/strong><\/p>\nAt the end of the mRNA coding is a stop codon which will end the elongation stage.\u00a0 The stop codon doesn’t call for a tRNA, but instead for a type of protein called a release factor, which will cause the entire complex (mRNA, ribosome, tRNA, and polypeptide) to break apart, releasing all of the components.<\/p>\n
<\/p>\n
<\/p>\n
\nFigure 5.7.4 Translation takes place in three stages: Initiation, Elongation and Termination.<\/em><\/figcaption><\/figure>\n<\/div>\nWatch this video “Protein Synthesis (Updated) with the Amoeba Sisters” to see this process in action:<\/p>\n
Figure 5.7.4 Translation takes place in three stages: Initiation, Elongation and Termination.<\/em>[\/caption]\r\n\r\n<\/div>\r\nWatch this video \"Protein Synthesis (Updated) with the Amoeba Sisters\" to see this process in action:\r\n\r\nhttps:\/\/www.youtube.com\/watch?v=oefAI2x2CQM&t=3s\r\nProtein Synthesis (Updated), Amoeba Sisters, 2018.<\/p>\r\n\r\n
What Happens Next?<\/h1>\r\n<\/div>\r\nAfter a polypeptide chain is synthesized, it may undergo additional processes. For example, it may assume a folded shape due to interactions between its amino acids. It may also bind with other polypeptides or with different types of molecules, such as [pb_glossary id=\"5651\"]lipids[\/pb_glossary] or [pb_glossary id=\"5655\"]carbohydrates[\/pb_glossary]. Many proteins travel to the [pb_glossary id=\"5485\"]Golgi apparatus[\/pb_glossary] within the [pb_glossary id=\"5465\"]cytoplasm[\/pb_glossary] to be modified for the specific job they will do.7 Summary<\/span>\r\n\r\n5.7 Summary<\/h2>\r\n<\/header>\r\n\r\n\r\n \t- Protein synthesis is the process in which\u00a0cells\u00a0make proteins. It occurs in two stages: transcription and translation.<\/li>\r\n \t
- Transcription is the transfer of genetic instructions in DNA to mRNA in the nucleus. It includes three steps: initiation, elongation, and termination. After the mRNA is processed, it carries the instructions to a ribosome in the cytoplasm.<\/li>\r\n \t
- Translation occurs at the ribosome, which consists of rRNA and proteins. In translation, the instructions in mRNA are read, and tRNA brings the correct sequence of amino acids to the ribosome. Then, rRNA helps bonds form between the amino acids, producing a polypeptide chain.<\/li>\r\n \t
- After a polypeptide chain is synthesized, it may undergo additional processing to form the finished protein.<\/li>\r\n<\/ul>\r\n<\/div>\r\n<\/div>\r\n\r\n
\r\n5.7 Review Questions<\/span><\/h1>\r\n<\/header>\r\n\r\n\r\n \t- Relate protein synthesis and its two major phases to the central dogma of molecular biology.<\/li>\r\n \t
- Explain how mRNA is processed before it leaves the nucleus.<\/li>\r\n \t
- What additional processes might\u00a0a polypeptide chain undergo after it is synthesized?<\/li>\r\n \t
- Where does transcription take place in eukaryotes?<\/li>\r\n \t
- Where does translation take place?<\/li>\r\n \t
- [h5p id=\"501\"]<\/li>\r\n<\/ol>\r\n<\/div>\r\n<\/div>\r\n
\r\n5.7 Explore More<\/span><\/h1>\r\n<\/header>\r\n\r\n\r\nhttps:\/\/youtu.be\/2zAGAmTkZNY\r\nProtein Synthesis, Teacher's Pet, 2014.<\/p>\r\n\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n \r\n
Attributions<\/h2>\r\nFigure 5.7.1<\/strong>\r\n\r\nHow proteins are made<\/a> by Nicolle Rager, National Science Foundation<\/a> on Wikimedia Commons is released into the public domain<\/a> (https:\/\/en.wikipedia.org\/wiki\/Public_domain).<\/i>\r\n\r\nFigure 5.7.2<\/strong>\r\n\r\nTranscription<\/a> by National Human Genome Research Institute<\/a>, (reworked and vectorized by Sulai)<\/a> on Wikimedia Commons is released into the public domain<\/a> (https:\/\/en.wikipedia.org\/wiki\/Public_domain).<\/i>\r\n\r\nFigure 5.7.3<\/strong>\r\n\r\nPre mRNA processing by Christine Miller is used under a CC BY-NC-SA 4.0<\/a>\u00a0 (https:\/\/creativecommons.org\/licenses\/by-nc-sa\/4.0\/) license.\r\n\r\nFigure 5.7.4<\/strong>\r\n\r\nTranslation<\/a>\u00a0by CNX OpenStax<\/a> on Wikimedia Commons is used under a CC BY 4.0<\/a> (https:\/\/creativecommons.org\/licenses\/by\/4.0) license.\r\nReferences<\/h2>\r\n
Amoeba Sisters. (2018, January 18) Protein synthesis (Updated). YouTube. https:\/\/www.youtube.com\/watch?v=oefAI2x2CQM&feature=youtu.be<\/p>\r\n
Parker, N., Schneegurt, M., Thi Tu, A-H., Lister, P., Forster, B.M. (2016, November 1). Microbiology [online]. Figure 11.15 Translation in bacteria begins with the formation of the initiation complex. In Microbiology<\/em> (Section 11-4). OpenStax. https:\/\/openstax.org\/books\/microbiology\/pages\/11-4-protein-synthesis-translation<\/p>\r\nTeacher's Pet. (2014, December 7). Protein synthesis. YouTube. https:\/\/www.youtube.com\/watch?v=2zAGAmTkZNY&feature=youtu.be<\/p>","rendered":"
<\/p>\nFigure 5.7.1 How proteins are made.<\/em><\/figcaption><\/figure>\nThe Art of Protein Synthesis<\/h1>\n
This amazing artwork (Figure 5.7.1) shows a process that takes place in the cells of all living things: the production of proteins. This process is called protein synthesis<\/a><\/strong>, and it\u00a0<\/strong>actually consists of two processes \u2014\u00a0transcription<\/a>\u00a0and translation<\/a>. In eukaryotic<\/a>\u00a0cells, transcription takes place in the\u00a0nucleus<\/a>. During transcription,\u00a0DNA<\/a>\u00a0is used as a template to make a molecule of messenger\u00a0RNA\u00a0(mRNA<\/a>). The molecule of mRNA then leaves the nucleus and goes to a\u00a0ribosome<\/a>\u00a0in the cytoplasm<\/a>, where translation occurs. During translation, the\u00a0genetic code in mRNA is read and used to make a polypeptide. These two processes are summed up by the\u00a0central dogma\u00a0of molecular biology:\u00a0DNA<\/a><\/strong>\u00a0<\/strong>\u2192<\/strong> RNA<\/a>\u00a0<\/strong>\u2192<\/strong>\u00a0<\/strong>Protein<\/a><\/strong>.<\/p>\n\nTranscription<\/h1>\n<\/div>\n
Transcription<\/strong>\u00a0is the first part of the\u00a0central dogma\u00a0of molecular biology:\u00a0DNA<\/strong>\u00a0<\/strong>\u2192<\/strong>\u00a0<\/strong>RNA<\/strong>. It is the transfer of genetic instructions in DNA to mRNA. During transcription, a strand of mRNA is made to complement a strand of DNA. You can see how this happens in Figure 5.7.2.<\/p>\nFigure 5.7.2 Transcription uses the sequence of bases in a strand of DNA to make a complementary strand of mRNA. Triplets are groups of three successive nucleotide bases in DNA. Codons are complementary groups of bases in mRNA.<\/em><\/figcaption><\/figure>\n<\/h2>\n
Transcription begins when the enzyme RNA polymerase binds to a region of a gene called the promoter sequence. This signals the DNA to unwind so the enzyme can \u201cread\u201d the bases of DNA.\u00a0 The two strands of DNA are named based on whether they will be used as a template for RNA or not.\u00a0 The strand that is used as a template is called the template strand, or can also be called the a<\/span><\/span>ntisense<\/span>\u00a0strand.\u00a0 The sequence of bases on the opposite strand of DNA is called the non-coding or sense strand.\u00a0<\/span><\/span> Once the DNA has opened, and RNA polymerase has attached, the RNA polymerase moves along the DNA, adding RNA <\/span>nucleotides to the growing mRNA strand.\u00a0 The template strand of DNA is used as to create mRNA through complementary base pairing. Once the<\/span> mRNA strand is complete, and it detaches from DNA. The result is\u00a0 a strand of mRNA that is nearly identical to the coding strand DNA – the only difference being that DNA uses the base thymine, and the mRNA uses uracil in the place of thymine<\/span><\/p>\nProcessing mRNA<\/h2>\n
In eukaryotes<\/a>, the new mRNA<\/a> is not yet ready for translation. At this stage, it is called pre-mRNA, and it must go through more processing before it leaves the\u00a0nucleus\u00a0as mature mRNA. The processing may include splicing, editing, and polyadenylation. These processes modify the mRNA in various ways. Such modifications allow a single gene to be used to make more than one\u00a0protein.<\/p>\n\n- Splicing <\/strong>removes introns from mRNA, as shown in Figure 5.7.3. Introns<\/strong>\u00a0are regions that do not code for the protein. The remaining mRNA consists only of regions called\u00a0exons<\/strong>\u00a0that do code for the protein. The ribonucleoproteins in the diagram are small\u00a0proteins\u00a0in the nucleus that contain RNA and are needed for the splicing process.<\/li>\n
- Editing <\/strong>changes some of the nucleotides in mRNA. For example, a human protein called APOB, which helps transport\u00a0lipids\u00a0in the\u00a0blood, has two different forms because of editing. One form is smaller than the other because editing adds an earlier stop signal in mRNA.<\/li>\n
- 5′ Capping\u00a0<\/strong>adds a methylated cap to the “head” of the mRNA.\u00a0 This cap protects the mRNA from breaking down, and helps the ribosomes know where to bind to the mRNA<\/li>\n
- Polyadenylation<\/a> <\/strong>adds a \u201ctail\u201d to the mRNA. The tail consists of a string of As (adenine bases). It signals the end of mRNA. It is also involved in exporting mRNA from the nucleus, and it protects mRNA from\u00a0enzymes that might break it down.<\/li>\n<\/ul>\n\n
Figure 5.7.3 Pre mRNA processing. mRNA requires processing before it leaves the nucleus.<\/em><\/figcaption><\/figure>\n<\/div>\n\nTranslation<\/h1>\n<\/div>\n
Translation<\/strong>\u00a0is the second part of the\u00a0central dogma\u00a0of molecular biology:\u00a0RNA <\/strong>\u2192<\/strong> Protein<\/strong>. It is the process in which the genetic code in mRNA<\/a> is read to make a protein<\/a>. Translation is illustrated in Figure 5.7.4. After mRNA leaves the nucleus<\/a>, it moves to a ribosome<\/a>, which consists of rRNA and proteins. The ribosome reads the sequence of codons<\/a> in mRNA, and molecules of tRNA<\/a> bring amino acids<\/a> to the ribosome in the correct sequence.<\/p>\nTranslation occurs in three stages: Initiation, Elongation and Termination.<\/p>\n
Initiation:<\/strong><\/p>\nAfter transcription in the nucleus, the mRNA exits through a nuclear pore and enters the cytoplasm.\u00a0 At the region on the mRNA containing the methylated cap and the start codon, the small and large subunits of the ribosome\u00a0 bind to the mRNA.\u00a0 These are then joined by a tRNA which contains the anticodons matching the start codon on the mRNA.\u00a0 This group of molecues (mRNA, ribosome, tRNA) is called an initiation complex.<\/p>\n
Elongation:<\/strong><\/p>\ntRNA keep bringing amino acids to the growing polypeptide according to complementary base pairing between the codons on the mRNA and the anticodons on the tRNA.\u00a0 As a tRNA moves into the ribosome, its amino acid is transferred to the growing polypeptide.\u00a0 Once this transfer is complete, the tRNA leaves the ribosome, the ribosome moves one codon length down the mRNA, and a new tRNA enters with its corresponding amino acid.\u00a0 This process repeats and the polypeptide grows.<\/p>\n
Termination<\/b>:<\/strong><\/p>\nAt the end of the mRNA coding is a stop codon which will end the elongation stage.\u00a0 The stop codon doesn’t call for a tRNA, but instead for a type of protein called a release factor, which will cause the entire complex (mRNA, ribosome, tRNA, and polypeptide) to break apart, releasing all of the components.<\/p>\n
<\/p>\n
<\/p>\n
\nFigure 5.7.4 Translation takes place in three stages: Initiation, Elongation and Termination.<\/em><\/figcaption><\/figure>\n<\/div>\nWatch this video “Protein Synthesis (Updated) with the Amoeba Sisters” to see this process in action:<\/p>\n
5.7 Summary<\/h2>\r\n<\/header>\r\n\r\n\r\n \t- Protein synthesis is the process in which\u00a0cells\u00a0make proteins. It occurs in two stages: transcription and translation.<\/li>\r\n \t
- Transcription is the transfer of genetic instructions in DNA to mRNA in the nucleus. It includes three steps: initiation, elongation, and termination. After the mRNA is processed, it carries the instructions to a ribosome in the cytoplasm.<\/li>\r\n \t
- Translation occurs at the ribosome, which consists of rRNA and proteins. In translation, the instructions in mRNA are read, and tRNA brings the correct sequence of amino acids to the ribosome. Then, rRNA helps bonds form between the amino acids, producing a polypeptide chain.<\/li>\r\n \t
- After a polypeptide chain is synthesized, it may undergo additional processing to form the finished protein.<\/li>\r\n<\/ul>\r\n<\/div>\r\n<\/div>\r\n\r\n
\r\n5.7 Review Questions<\/span><\/h1>\r\n<\/header>\r\n\r\n\r\n \t- Relate protein synthesis and its two major phases to the central dogma of molecular biology.<\/li>\r\n \t
- Explain how mRNA is processed before it leaves the nucleus.<\/li>\r\n \t
- What additional processes might\u00a0a polypeptide chain undergo after it is synthesized?<\/li>\r\n \t
- Where does transcription take place in eukaryotes?<\/li>\r\n \t
- Where does translation take place?<\/li>\r\n \t
- [h5p id=\"501\"]<\/li>\r\n<\/ol>\r\n<\/div>\r\n<\/div>\r\n
\r\n5.7 Explore More<\/span><\/h1>\r\n<\/header>\r\n\r\n\r\nhttps:\/\/youtu.be\/2zAGAmTkZNY\r\nProtein Synthesis, Teacher's Pet, 2014.<\/p>\r\n\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n \r\n
Attributions<\/h2>\r\nFigure 5.7.1<\/strong>\r\n\r\nHow proteins are made<\/a> by Nicolle Rager, National Science Foundation<\/a> on Wikimedia Commons is released into the public domain<\/a> (https:\/\/en.wikipedia.org\/wiki\/Public_domain).<\/i>\r\n\r\nFigure 5.7.2<\/strong>\r\n\r\nTranscription<\/a> by National Human Genome Research Institute<\/a>, (reworked and vectorized by Sulai)<\/a> on Wikimedia Commons is released into the public domain<\/a> (https:\/\/en.wikipedia.org\/wiki\/Public_domain).<\/i>\r\n\r\nFigure 5.7.3<\/strong>\r\n\r\nPre mRNA processing by Christine Miller is used under a CC BY-NC-SA 4.0<\/a>\u00a0 (https:\/\/creativecommons.org\/licenses\/by-nc-sa\/4.0\/) license.\r\n\r\nFigure 5.7.4<\/strong>\r\n\r\nTranslation<\/a>\u00a0by CNX OpenStax<\/a> on Wikimedia Commons is used under a CC BY 4.0<\/a> (https:\/\/creativecommons.org\/licenses\/by\/4.0) license.\r\nReferences<\/h2>\r\n
Amoeba Sisters. (2018, January 18) Protein synthesis (Updated). YouTube. https:\/\/www.youtube.com\/watch?v=oefAI2x2CQM&feature=youtu.be<\/p>\r\n
Parker, N., Schneegurt, M., Thi Tu, A-H., Lister, P., Forster, B.M. (2016, November 1). Microbiology [online]. Figure 11.15 Translation in bacteria begins with the formation of the initiation complex. In Microbiology<\/em> (Section 11-4). OpenStax. https:\/\/openstax.org\/books\/microbiology\/pages\/11-4-protein-synthesis-translation<\/p>\r\nTeacher's Pet. (2014, December 7). Protein synthesis. YouTube. https:\/\/www.youtube.com\/watch?v=2zAGAmTkZNY&feature=youtu.be<\/p>","rendered":"
<\/p>\nFigure 5.7.1 How proteins are made.<\/em><\/figcaption><\/figure>\nThe Art of Protein Synthesis<\/h1>\n
This amazing artwork (Figure 5.7.1) shows a process that takes place in the cells of all living things: the production of proteins. This process is called protein synthesis<\/a><\/strong>, and it\u00a0<\/strong>actually consists of two processes \u2014\u00a0transcription<\/a>\u00a0and translation<\/a>. In eukaryotic<\/a>\u00a0cells, transcription takes place in the\u00a0nucleus<\/a>. During transcription,\u00a0DNA<\/a>\u00a0is used as a template to make a molecule of messenger\u00a0RNA\u00a0(mRNA<\/a>). The molecule of mRNA then leaves the nucleus and goes to a\u00a0ribosome<\/a>\u00a0in the cytoplasm<\/a>, where translation occurs. During translation, the\u00a0genetic code in mRNA is read and used to make a polypeptide. These two processes are summed up by the\u00a0central dogma\u00a0of molecular biology:\u00a0DNA<\/a><\/strong>\u00a0<\/strong>\u2192<\/strong> RNA<\/a>\u00a0<\/strong>\u2192<\/strong>\u00a0<\/strong>Protein<\/a><\/strong>.<\/p>\n\nTranscription<\/h1>\n<\/div>\n
Transcription<\/strong>\u00a0is the first part of the\u00a0central dogma\u00a0of molecular biology:\u00a0DNA<\/strong>\u00a0<\/strong>\u2192<\/strong>\u00a0<\/strong>RNA<\/strong>. It is the transfer of genetic instructions in DNA to mRNA. During transcription, a strand of mRNA is made to complement a strand of DNA. You can see how this happens in Figure 5.7.2.<\/p>\nFigure 5.7.2 Transcription uses the sequence of bases in a strand of DNA to make a complementary strand of mRNA. Triplets are groups of three successive nucleotide bases in DNA. Codons are complementary groups of bases in mRNA.<\/em><\/figcaption><\/figure>\n<\/h2>\n
Transcription begins when the enzyme RNA polymerase binds to a region of a gene called the promoter sequence. This signals the DNA to unwind so the enzyme can \u201cread\u201d the bases of DNA.\u00a0 The two strands of DNA are named based on whether they will be used as a template for RNA or not.\u00a0 The strand that is used as a template is called the template strand, or can also be called the a<\/span><\/span>ntisense<\/span>\u00a0strand.\u00a0 The sequence of bases on the opposite strand of DNA is called the non-coding or sense strand.\u00a0<\/span><\/span> Once the DNA has opened, and RNA polymerase has attached, the RNA polymerase moves along the DNA, adding RNA <\/span>nucleotides to the growing mRNA strand.\u00a0 The template strand of DNA is used as to create mRNA through complementary base pairing. Once the<\/span> mRNA strand is complete, and it detaches from DNA. The result is\u00a0 a strand of mRNA that is nearly identical to the coding strand DNA – the only difference being that DNA uses the base thymine, and the mRNA uses uracil in the place of thymine<\/span><\/p>\nProcessing mRNA<\/h2>\n
In eukaryotes<\/a>, the new mRNA<\/a> is not yet ready for translation. At this stage, it is called pre-mRNA, and it must go through more processing before it leaves the\u00a0nucleus\u00a0as mature mRNA. The processing may include splicing, editing, and polyadenylation. These processes modify the mRNA in various ways. Such modifications allow a single gene to be used to make more than one\u00a0protein.<\/p>\n\n- Splicing <\/strong>removes introns from mRNA, as shown in Figure 5.7.3. Introns<\/strong>\u00a0are regions that do not code for the protein. The remaining mRNA consists only of regions called\u00a0exons<\/strong>\u00a0that do code for the protein. The ribonucleoproteins in the diagram are small\u00a0proteins\u00a0in the nucleus that contain RNA and are needed for the splicing process.<\/li>\n
- Editing <\/strong>changes some of the nucleotides in mRNA. For example, a human protein called APOB, which helps transport\u00a0lipids\u00a0in the\u00a0blood, has two different forms because of editing. One form is smaller than the other because editing adds an earlier stop signal in mRNA.<\/li>\n
- 5′ Capping\u00a0<\/strong>adds a methylated cap to the “head” of the mRNA.\u00a0 This cap protects the mRNA from breaking down, and helps the ribosomes know where to bind to the mRNA<\/li>\n
- Polyadenylation<\/a> <\/strong>adds a \u201ctail\u201d to the mRNA. The tail consists of a string of As (adenine bases). It signals the end of mRNA. It is also involved in exporting mRNA from the nucleus, and it protects mRNA from\u00a0enzymes that might break it down.<\/li>\n<\/ul>\n\n
Figure 5.7.3 Pre mRNA processing. mRNA requires processing before it leaves the nucleus.<\/em><\/figcaption><\/figure>\n<\/div>\n\nTranslation<\/h1>\n<\/div>\n
Translation<\/strong>\u00a0is the second part of the\u00a0central dogma\u00a0of molecular biology:\u00a0RNA <\/strong>\u2192<\/strong> Protein<\/strong>. It is the process in which the genetic code in mRNA<\/a> is read to make a protein<\/a>. Translation is illustrated in Figure 5.7.4. After mRNA leaves the nucleus<\/a>, it moves to a ribosome<\/a>, which consists of rRNA and proteins. The ribosome reads the sequence of codons<\/a> in mRNA, and molecules of tRNA<\/a> bring amino acids<\/a> to the ribosome in the correct sequence.<\/p>\nTranslation occurs in three stages: Initiation, Elongation and Termination.<\/p>\n
Initiation:<\/strong><\/p>\nAfter transcription in the nucleus, the mRNA exits through a nuclear pore and enters the cytoplasm.\u00a0 At the region on the mRNA containing the methylated cap and the start codon, the small and large subunits of the ribosome\u00a0 bind to the mRNA.\u00a0 These are then joined by a tRNA which contains the anticodons matching the start codon on the mRNA.\u00a0 This group of molecues (mRNA, ribosome, tRNA) is called an initiation complex.<\/p>\n
Elongation:<\/strong><\/p>\ntRNA keep bringing amino acids to the growing polypeptide according to complementary base pairing between the codons on the mRNA and the anticodons on the tRNA.\u00a0 As a tRNA moves into the ribosome, its amino acid is transferred to the growing polypeptide.\u00a0 Once this transfer is complete, the tRNA leaves the ribosome, the ribosome moves one codon length down the mRNA, and a new tRNA enters with its corresponding amino acid.\u00a0 This process repeats and the polypeptide grows.<\/p>\n
Termination<\/b>:<\/strong><\/p>\nAt the end of the mRNA coding is a stop codon which will end the elongation stage.\u00a0 The stop codon doesn’t call for a tRNA, but instead for a type of protein called a release factor, which will cause the entire complex (mRNA, ribosome, tRNA, and polypeptide) to break apart, releasing all of the components.<\/p>\n
<\/p>\n
<\/p>\n
\nFigure 5.7.4 Translation takes place in three stages: Initiation, Elongation and Termination.<\/em><\/figcaption><\/figure>\n<\/div>\nWatch this video “Protein Synthesis (Updated) with the Amoeba Sisters” to see this process in action:<\/p>\n
- \r\n \t
- Protein synthesis is the process in which\u00a0cells\u00a0make proteins. It occurs in two stages: transcription and translation.<\/li>\r\n \t
- Transcription is the transfer of genetic instructions in DNA to mRNA in the nucleus. It includes three steps: initiation, elongation, and termination. After the mRNA is processed, it carries the instructions to a ribosome in the cytoplasm.<\/li>\r\n \t
- Translation occurs at the ribosome, which consists of rRNA and proteins. In translation, the instructions in mRNA are read, and tRNA brings the correct sequence of amino acids to the ribosome. Then, rRNA helps bonds form between the amino acids, producing a polypeptide chain.<\/li>\r\n \t
- After a polypeptide chain is synthesized, it may undergo additional processing to form the finished protein.<\/li>\r\n<\/ul>\r\n<\/div>\r\n<\/div>\r\n\r\n
\r\n 5.7 Review Questions<\/span><\/h1>\r\n<\/header>\r\n
\r\n- \r\n \t
- Relate protein synthesis and its two major phases to the central dogma of molecular biology.<\/li>\r\n \t
- Explain how mRNA is processed before it leaves the nucleus.<\/li>\r\n \t
- What additional processes might\u00a0a polypeptide chain undergo after it is synthesized?<\/li>\r\n \t
- Where does transcription take place in eukaryotes?<\/li>\r\n \t
- Where does translation take place?<\/li>\r\n \t
- [h5p id=\"501\"]<\/li>\r\n<\/ol>\r\n<\/div>\r\n<\/div>\r\n
\r\n 5.7 Explore More<\/span><\/h1>\r\n<\/header>\r\n
\r\n\r\nhttps:\/\/youtu.be\/2zAGAmTkZNY\r\nProtein Synthesis, Teacher's Pet, 2014.<\/p>\r\n\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n \r\n
Attributions<\/h2>\r\nFigure 5.7.1<\/strong>\r\n\r\nHow proteins are made<\/a> by Nicolle Rager, National Science Foundation<\/a> on Wikimedia Commons is released into the public domain<\/a> (https:\/\/en.wikipedia.org\/wiki\/Public_domain).<\/i>\r\n\r\nFigure 5.7.2<\/strong>\r\n\r\nTranscription<\/a> by National Human Genome Research Institute<\/a>, (reworked and vectorized by Sulai)<\/a> on Wikimedia Commons is released into the public domain<\/a> (https:\/\/en.wikipedia.org\/wiki\/Public_domain).<\/i>\r\n\r\nFigure 5.7.3<\/strong>\r\n\r\nPre mRNA processing by Christine Miller is used under a CC BY-NC-SA 4.0<\/a>\u00a0 (https:\/\/creativecommons.org\/licenses\/by-nc-sa\/4.0\/) license.\r\n\r\nFigure 5.7.4<\/strong>\r\n\r\nTranslation<\/a>\u00a0by CNX OpenStax<\/a> on Wikimedia Commons is used under a CC BY 4.0<\/a> (https:\/\/creativecommons.org\/licenses\/by\/4.0) license.\r\n
References<\/h2>\r\n
Amoeba Sisters. (2018, January 18) Protein synthesis (Updated). YouTube. https:\/\/www.youtube.com\/watch?v=oefAI2x2CQM&feature=youtu.be<\/p>\r\n
Parker, N., Schneegurt, M., Thi Tu, A-H., Lister, P., Forster, B.M. (2016, November 1). Microbiology [online]. Figure 11.15 Translation in bacteria begins with the formation of the initiation complex. In Microbiology<\/em> (Section 11-4). OpenStax. https:\/\/openstax.org\/books\/microbiology\/pages\/11-4-protein-synthesis-translation<\/p>\r\n
Teacher's Pet. (2014, December 7). Protein synthesis. YouTube. https:\/\/www.youtube.com\/watch?v=2zAGAmTkZNY&feature=youtu.be<\/p>","rendered":"
<\/p>\n
Figure 5.7.1 How proteins are made.<\/em><\/figcaption><\/figure>\n The Art of Protein Synthesis<\/h1>\n
This amazing artwork (Figure 5.7.1) shows a process that takes place in the cells of all living things: the production of proteins. This process is called protein synthesis<\/a><\/strong>, and it\u00a0<\/strong>actually consists of two processes \u2014\u00a0transcription<\/a>\u00a0and translation<\/a>. In eukaryotic<\/a>\u00a0cells, transcription takes place in the\u00a0nucleus<\/a>. During transcription,\u00a0DNA<\/a>\u00a0is used as a template to make a molecule of messenger\u00a0RNA\u00a0(mRNA<\/a>). The molecule of mRNA then leaves the nucleus and goes to a\u00a0ribosome<\/a>\u00a0in the cytoplasm<\/a>, where translation occurs. During translation, the\u00a0genetic code in mRNA is read and used to make a polypeptide. These two processes are summed up by the\u00a0central dogma\u00a0of molecular biology:\u00a0DNA<\/a><\/strong>\u00a0<\/strong>\u2192<\/strong> RNA<\/a>\u00a0<\/strong>\u2192<\/strong>\u00a0<\/strong>Protein<\/a><\/strong>.<\/p>\n
\nTranscription<\/h1>\n<\/div>\n
Transcription<\/strong>\u00a0is the first part of the\u00a0central dogma\u00a0of molecular biology:\u00a0DNA<\/strong>\u00a0<\/strong>\u2192<\/strong>\u00a0<\/strong>RNA<\/strong>. It is the transfer of genetic instructions in DNA to mRNA. During transcription, a strand of mRNA is made to complement a strand of DNA. You can see how this happens in Figure 5.7.2.<\/p>\n
Figure 5.7.2 Transcription uses the sequence of bases in a strand of DNA to make a complementary strand of mRNA. Triplets are groups of three successive nucleotide bases in DNA. Codons are complementary groups of bases in mRNA.<\/em><\/figcaption><\/figure>\n <\/h2>\n
Transcription begins when the enzyme RNA polymerase binds to a region of a gene called the promoter sequence. This signals the DNA to unwind so the enzyme can \u201cread\u201d the bases of DNA.\u00a0 The two strands of DNA are named based on whether they will be used as a template for RNA or not.\u00a0 The strand that is used as a template is called the template strand, or can also be called the a<\/span><\/span>ntisense<\/span>\u00a0strand.\u00a0 The sequence of bases on the opposite strand of DNA is called the non-coding or sense strand.\u00a0<\/span><\/span> Once the DNA has opened, and RNA polymerase has attached, the RNA polymerase moves along the DNA, adding RNA <\/span>nucleotides to the growing mRNA strand.\u00a0 The template strand of DNA is used as to create mRNA through complementary base pairing. Once the<\/span> mRNA strand is complete, and it detaches from DNA. The result is\u00a0 a strand of mRNA that is nearly identical to the coding strand DNA – the only difference being that DNA uses the base thymine, and the mRNA uses uracil in the place of thymine<\/span><\/p>\n
Processing mRNA<\/h2>\n
In eukaryotes<\/a>, the new mRNA<\/a> is not yet ready for translation. At this stage, it is called pre-mRNA, and it must go through more processing before it leaves the\u00a0nucleus\u00a0as mature mRNA. The processing may include splicing, editing, and polyadenylation. These processes modify the mRNA in various ways. Such modifications allow a single gene to be used to make more than one\u00a0protein.<\/p>\n
- \n
- Splicing <\/strong>removes introns from mRNA, as shown in Figure 5.7.3. Introns<\/strong>\u00a0are regions that do not code for the protein. The remaining mRNA consists only of regions called\u00a0exons<\/strong>\u00a0that do code for the protein. The ribonucleoproteins in the diagram are small\u00a0proteins\u00a0in the nucleus that contain RNA and are needed for the splicing process.<\/li>\n
- Editing <\/strong>changes some of the nucleotides in mRNA. For example, a human protein called APOB, which helps transport\u00a0lipids\u00a0in the\u00a0blood, has two different forms because of editing. One form is smaller than the other because editing adds an earlier stop signal in mRNA.<\/li>\n
- 5′ Capping\u00a0<\/strong>adds a methylated cap to the “head” of the mRNA.\u00a0 This cap protects the mRNA from breaking down, and helps the ribosomes know where to bind to the mRNA<\/li>\n
- Polyadenylation<\/a> <\/strong>adds a \u201ctail\u201d to the mRNA. The tail consists of a string of As (adenine bases). It signals the end of mRNA. It is also involved in exporting mRNA from the nucleus, and it protects mRNA from\u00a0enzymes that might break it down.<\/li>\n<\/ul>\n
\nFigure 5.7.3 Pre mRNA processing. mRNA requires processing before it leaves the nucleus.<\/em><\/figcaption><\/figure>\n<\/div>\n \nTranslation<\/h1>\n<\/div>\n
Translation<\/strong>\u00a0is the second part of the\u00a0central dogma\u00a0of molecular biology:\u00a0RNA <\/strong>\u2192<\/strong> Protein<\/strong>. It is the process in which the genetic code in mRNA<\/a> is read to make a protein<\/a>. Translation is illustrated in Figure 5.7.4. After mRNA leaves the nucleus<\/a>, it moves to a ribosome<\/a>, which consists of rRNA and proteins. The ribosome reads the sequence of codons<\/a> in mRNA, and molecules of tRNA<\/a> bring amino acids<\/a> to the ribosome in the correct sequence.<\/p>\n
Translation occurs in three stages: Initiation, Elongation and Termination.<\/p>\n
Initiation:<\/strong><\/p>\n
After transcription in the nucleus, the mRNA exits through a nuclear pore and enters the cytoplasm.\u00a0 At the region on the mRNA containing the methylated cap and the start codon, the small and large subunits of the ribosome\u00a0 bind to the mRNA.\u00a0 These are then joined by a tRNA which contains the anticodons matching the start codon on the mRNA.\u00a0 This group of molecues (mRNA, ribosome, tRNA) is called an initiation complex.<\/p>\n
Elongation:<\/strong><\/p>\n
tRNA keep bringing amino acids to the growing polypeptide according to complementary base pairing between the codons on the mRNA and the anticodons on the tRNA.\u00a0 As a tRNA moves into the ribosome, its amino acid is transferred to the growing polypeptide.\u00a0 Once this transfer is complete, the tRNA leaves the ribosome, the ribosome moves one codon length down the mRNA, and a new tRNA enters with its corresponding amino acid.\u00a0 This process repeats and the polypeptide grows.<\/p>\n
Termination<\/b>:<\/strong><\/p>\n
At the end of the mRNA coding is a stop codon which will end the elongation stage.\u00a0 The stop codon doesn’t call for a tRNA, but instead for a type of protein called a release factor, which will cause the entire complex (mRNA, ribosome, tRNA, and polypeptide) to break apart, releasing all of the components.<\/p>\n
<\/p>\n
<\/p>\n
\nFigure 5.7.4 Translation takes place in three stages: Initiation, Elongation and Termination.<\/em><\/figcaption><\/figure>\n<\/div>\n Watch this video “Protein Synthesis (Updated) with the Amoeba Sisters” to see this process in action:<\/p>\n
- Editing <\/strong>changes some of the nucleotides in mRNA. For example, a human protein called APOB, which helps transport\u00a0lipids\u00a0in the\u00a0blood, has two different forms because of editing. One form is smaller than the other because editing adds an earlier stop signal in mRNA.<\/li>\n
- Splicing <\/strong>removes introns from mRNA, as shown in Figure 5.7.3. Introns<\/strong>\u00a0are regions that do not code for the protein. The remaining mRNA consists only of regions called\u00a0exons<\/strong>\u00a0that do code for the protein. The ribonucleoproteins in the diagram are small\u00a0proteins\u00a0in the nucleus that contain RNA and are needed for the splicing process.<\/li>\n
![How proteins are made<\/a> by Nicolle Rager,](\"https:\/\/commons.wikimedia.org\/wiki\/File:How_proteins_are_made_NSF.jpg\"){kind=link}
![Transcription<\/a> by](\"https:\/\/upload.wikimedia.org\/wikipedia\/commons\/3\/36\/DNA_transcription.svg\"){kind=link}
![Translation<\/a>\u00a0by](\"https:\/\/commons.wikimedia.org\/wiki\/File:OSC_Microbio_11_04_TlnInit.jpg\"){kind=link}