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Published byHarold Gregory Modified over 8 years ago
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Molecular Genetics Transcription
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the process where the DNA code is used to make a complementary mRNA strand three main stages: 1. initiation 2. elongation 3. termination
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Initiation (Image from: http://sandwalk.blogspot.com/2008/09/how-rna-polymerase-binds-to-dna.html) RNA polymerase binds to the promoter sequence
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Promoter Sequence right beside the start of a gene (upstream of the gene) recognition site for RNA polymerase to bind to the DNA high in adenine and thymine (easier to break H-bonds)
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Elongation (Image from: http://dna-rna.net/2011/08/24/rna-transcription/) RNA polymerase opens the double helix synthesizes mRNA by adding ribonucleotides from 5’ to 3’
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Elongation the template strand of the DNA is used as a template for making the complementary mRNA strand the coding strand of the DNA is not used for transcription
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Termination (Image from: http://www.stat.berkeley.edu/users/terry/Classes/s260.1998/Week12/week12/node5.html) when RNA polymerase reaches the terminator sequence, transcription stops and mRNA is released
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(Image from: http://www.nature.com/scitable/topicpage/translation-dna-to-mrna-to-protein-393)
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Transciption Summary (Image from: http://www.tokresource.org/tok_classes/biobiobio/biomenu/transcription_translation/index.htm)
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Transcription Animations Simple animation & quiz: http://highered.mcgraw- hill.com/sites/0072507470/student_view0/cha pter3/animation__mrna_synthesis__transcript ion___quiz_1_.html Slideshow animation of transcription: http://www- class.unl.edu/biochem/gp2/m_biology/animati on/gene/gene_a2.html
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Transcription Animations Narrated animation & quiz: http://bcs.whfreeman.com/thelifewire/cont ent/chp12/1202001.html
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Posttranscriptional Modifications in eukaryotic cells, the primary transcript, will need to undergo three modifications before leaving the nucleus
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Addition of 5’ Cap (Image from: http://en.wikipedia.org/wiki/File:5'_cap_structure.png) a 7-methyl guanosine is added to the start of the primary transcript to prevent digestion in the cytoplasm. This is called the 5’cap.
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Addition of Poly-A Tail approximately 200 adenine ribonucleotides are added to the 3’ end by poly-A polymerase this is called the poly-A tail.
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Removal of Introns the eukaryotic genome consists of coding regions (exons) and non-coding regions (introns) proteins called spliceosomes cut the introns out of the primary transcript and rejoin the exons
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Removal of Introns Image from: http://www.britannica.com/EBchecked/media/114928/Genes-are-made-up-of-promoter-regions-and- alternating-regions
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mRNA Transcript (Image from: http://www.biology.arizona.edu/molecular_bio/problem_sets/mol_genetics_of_eukaryotes/01t.html) the mRNA is ready to leave the nucleus for translation and it is now called the mRNA transcript
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Animation Simple animation of post-transcriptional modifications: http://www.execulink.com/~ekimmel/mrna _flash.htm
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