Lecture 6 Exam 4

Lecture 6 Exam 4 - Biology 313 Lecture 39 Dec 8, 2010 The...

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Biology 313 Lecture 39 Dec 8, 2010
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The Concept of the Gene The gene includes DNA sequences that code for all exons, introns, and those sequences at the beginning and end of the RNA that are not translated into a protein, including the entire transcription unit – the promoter, the RNA coding sequence, and the terminator.
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Structure of mature mRNA: primary regions 5′ u nt ranslated r egion ( 5′- UTR , or leader sequence); not translated into protein Protein coding region – defined by a START codon (translation initiation codon, or initiating ATG) and STOP codon (translation termination codon) 3′ u nt ranslated r egion ( 3’- UTR ); not translated into protein
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3 regions of mature mRNA Shine–Dalgarno sequence is in 5’ UTR of prokaryote mRNAs for ribosome binding (next chapter)
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Eukaryotic mRNA is made in the nucleus as a pre-mRNA that is then extensively processed Tx and translation are coupled events (occur together) in prokaryotes, but not in eukaryotes; this allows time and space for modifications to pre-mRNAs in eukaryotes
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Pre-mRNA processing: 3 major events 1. Capping of 5’-end of mRNA 2. Polyadenylation ; addition of poly(A) tail to 3’-end of mRNA 3. Splicing : all nuclear pre-mRNAs are spliced by the spliceosome (I will not discuss self-splicing introns, which occur in some genes for rRNAs and tRNAs and for genes in mitochondria and chloroplasts)
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5’- Capping The addition of the 5′ cap : A nucleotide with 7-methylguanine is added to the 5’ end of all mRNAs The cap helps initiate translation: the cap binds proteins that are recognized by the ribosome, which then scans downstream for an initiating ATG
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5’- Capping 7-methylguanine is added
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Pre-mRNA processing: polyadenylation Polyadenylation : addition of a poly(A) tail pre-mRNA is cleaved 11-30 nucleotides downstream from a AAUAAA consensus sequence in the 3’-UTR 50 ~ 250 adenine nucleotides are added to the cleavage site by poly(A) polymerase poly(A) tail confers stability on mRNA
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Pre-mRNA processing: polyadenylation
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Lecture 6 Exam 4 - Biology 313 Lecture 39 Dec 8, 2010 The...

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