Unit 8handout - Review of Unit 7 1. Chromatin structure...

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1. Chromatin structure Packing of DNA to fit in nucleus First order packing - Nucleosomes Histones – major protein 1. 30 nm fiber – a helix of nucleosomes, 6 per turn 2. Higher order loops, 10 – 100 kb around a protein scaffold 3. Nucleosomes inhibit transcription 4. Histone acetylation/deacetylation– affect transcription 5. Nucleosome positioning 6. DNaseI can be used to study chromatin state 7. Transcription factors can affect chromatin structure acetylation status preempt nucleosome formation 8. “Spooling Model”-Nucleosomes and transcription elongation Review of Unit 7
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Outine of Unit 8 1. Post-transcriptional modifications are unique to eukaryotes 2. 5’ cap 3. Poly(A) tail 4. Splicing Recognition sequences for splicing Components of the spliceosome Alternative splicing
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Unit 8: Post-transcriptional processes Reading: Weaver pp. 399-421, 444-467
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Eukaryote vs. Prokaryote In prokaryotes, transcription and translation are coupled (occur simultaneously) In eukaryotes, transcription and translation occur in different cellular compartments; mRNA must be transported from the nucleus to cytoplasm before translation Transport of RNA (by specific transport proteins) to the cytoplasm is another step at which regulation can occur in eukaryotes
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Heterochromatin (condensed) Euchromatin (open, active)
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In prokaryotes, transcription termination occurs at a specific site; the intact RNA is then translated into proteins on ribosomes In eukaryotes, transcription termination is not well-understood. After termination the transcript undergoes several modifications before translation can occur Prokaryotic RNAs are not modified Eukaryote vs. Prokaryote
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Three Major Types Of RNA Processing Primary transcript=copy of DNA modification Removal of introns Export to cytoplasm hnRNA or pre-mRNA
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Addition of 5' CAP to mRNA 5' end of transcript 3' H H 5’ phosphate
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2. Methylation of guanine 3. Methylation of 1-2 nts on RNA (depends on organism) Addition of 5' CAP to mRNA 1. Add GTP using 5'-5' linkage 5' end of transcript 3'
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Capping
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5’ cap is added when the transcript is ~20 – 30 nt in length (transcription is still in process) Guanylyl transferase binds to
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Unit 8handout - Review of Unit 7 1. Chromatin structure...

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