Transcription and Post Transcript Modification

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1 Transcription and Post Transcript Modification

2 You Should Be Able To 1. Describe transcription. 2. Compare and contrast eukaryotic + prokaryotic transcription. 3. Explain mrna processing in eukaryotes. 4. Describe how transcription can be controlled in eukaryotes.

3 Central Dogma DNA Transcription mrna Translation ribosome mrna protein

4 Transcription mrna DNA RNA Polymerase II

5 1. RNA Polymerase II attaches to DNA (initiation). 2. RNA Polymerase II makes an RNA strand (elongation). 3. RNA Polymerase detaches from DNA (termination).

6 Prokaryotes ß upstream of gene gene à

7 Eukaryotes Promoter region

8 Eukaryotes

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10 Prok: RNA Pol II + Sigma Factor. at the -35 box and -10 box Euk: RNA Pol II + Transcr. Factors at the -30 box, aka the TATA box 1. RNA Polymerase II attaches to DNA (initiation). 2. RNA Polymerase II makes an RNA strand (elongation). 3. RNA Polymerase detaches from DNA (termination).

11 Non-template (coding) strand Template strand DNA RNA Phosphodiester linkage is formed by RNA polymerase after base pairing occurs Incoming NTP (monomer) RNA Hydrogen bonds form between complementary base pairs DNA template 2017 Pearson Education, Inc. Figure 17.1

12 Prok: RNA Pol II + Sigma Factor. at the -35 box and -10 box Euk: RNA Pol II + Transcr. Factors at the -30 box, aka the TATA box 1. RNA Polymerase II attaches to DNA (initiation). 2. RNA Polymerase II makes an RNA strand (elongation). 3. RNA Polymerase detaches from DNA (termination).

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14 Fig Transcription Termination in Eukaryotes: The sequence AAUAAA Signals for the RNA transcript to be cleaved.

15 Prok: RNA Pol II + Sigma Factor. at the -35 box and -10 box Euk: RNA Pol II + Transcr. Factors at the -30 box, aka the TATA box 1. RNA Polymerase II attaches to DNA (initiation). 2. RNA Polymerase II makes an RNA strand (elongation). 3. RNA Polymerase detaches from DNA (termination). Prok: RNA Hairpin forms Euk: Termination sequence + Enzymes

16 Central Dogma DNA Transcription mrna Translation mrna Ribosome Protein

17 Eukaryotes à The RNA Transcript

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20 Eukaryotes à The RNA Transcript

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22 Introns and Exons Intron: A region of a eukaryotic gene that is transcribed into RNA but is later removed by a spliceosome. Exon: A transcribed region of a eukaryotic gene or region of a primary transcript that is retained in mature RNA.

23 Anatomy of a Eukaryotic Gene

24 Transcription Primary transcript Introns Cut Out Cap and Tail Added Mature mrna

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26 Fig RNA transcript (pre-mrna) Exon 1 Intron Exon 2 Protein snrna snrnps Other proteins Spliceosome 5 Spliceosome components 5 mrna Exon 1 Exon 2 Cut-out intron

27 Central Dogma DNA mrna ribosome mrna Mature mrna protein

28 5 Protein-coding segment Polyadenylation signal G P P P AAUAAA AAA AAA 5 Cap 5 UTR Start codon Stop codon 3 UTR Poly-A tail but only this region gets translated this region was transcribed 3 Fig. 17-9

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31 Humans have ~20,000 genes and >100,000 types of proteins. How is this possible if DNAàmRNAàProtein?

32 Alternative Gene Splicing Fig RNA transcript (pre-mrna) Exon 1 Intron Exon 2 Protein snrna snrnps Other proteins Spliceosome

33 Alternative Gene Splicing Primary transcript Spliceosome

34 Alternative Gene Splicing

35 Fig. 17-3b-3 Nuclear envelope TRANSCRIPTION DNA RNA PROCESSING Pre-mRNA mrna TRANSLATION Ribosome Polypeptide (b) Eukaryotic cell

36 Regulation of Gene Expression Eukaryotes

37 Regulation of Gene Expression There are at least 300 different kinds of cells in the human body. Most of them have identical DNA.

38 In order for different types cells to produce different types of proteins, they need to produce different types of mrna.

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41 Campbell 8e, Fig. 18.9

42 Controlling Gene Expression: Enhancers and Activators Provide a way to turn on specific genes in specific cells Different genes have different enhancers Different cells have different activators Campbell 8e, Fig

43 Controlling Gene Expression: Enhancers and Activators Tissue- and cell-type specific gene expression Liver cells make albumin, but not crystallin Lens cells make crystallin, but not albumin Campbell 8e, Fig

44 Controlling Gene Expression: Enhancers and Activators - Different genes have different enhancers. - Different cell types have different activators. Campbell 8e, Fig

45 You Should Be Able To 1. Describe transcription. 2. Compare and contrast eukaryotic + prokaryotic transcription. 3. Explain mrna processing in eukaryotes. 4. Describe how transcription can be controlled in eukaryotes.

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