Lecture 3.3 Notes

Lecture 3.3 Notes - Notes, 3/3/10 Transcription and...

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Notes, 3/3/10 Transcription and translation in Eukarya Transcription: •Multiple RNA polymerases in Eukarya •RNAP I – transcription of large (18s and 28s) RNAs •RNAP II – transcription of mRNA •RNAP III - transcription of small rRNAs and other small RNAs •Each RNAP recognizes a distinct class of promoters •Archeael RNAP most resembles RNAP II •All eukaryotic RNAPs and archaeal RNAP large proteins w/ 8 or more subunits in contrast to relatively simple structure of bacterial RNAP (4 subunits) •Eukaryotic RNAP II •Requirement for host of transcription factors required for promoter recognition in contrast to bacterial RNAP, which can recognize promoters on its own •TATA and INIT regions as well as multiple other regions (enhancers) that bind generalized and tissue-specific transcription factors complex and flexible promoter organization •Carboxy-terminal domain (CTD), consisting of multiple copies of repetitive amino acid sequence, recruits factors necessary for cotranslational capping, polyadenylation and splicing. •Archaeal RNAP and promoters similar in general structure and organization to eukaryotic counterparts although simpler. •Bacterial-type RNAP found in mitochondria and chloroplasts, reflecting the prokaryotic origin of these organelles Translation: •Protein synthesis in Eukarya more complex than in Bacteria . •Eukaryotic ribosomes larger and contain more proteins and RNAs •Archaea shares some features with Bacteria (size of ribosomes, polycistronic mRNA, no cap on mRNA) and others with Eukarya (initiation with met rather than f-met, inhibition by diptheria toxin, multiple initiation and elongation factors) (See Table 8.2) RNA interference •Found only in eukaryotes •dsRNA cleaved by dicer into short segments (siRNA) •RNA-induced silencing complex (RISC) binds siRNA and separates strands •Binding of RISC to mRNA and degradation of mRNAs complementary to RISC-associated siRNA (when perfect complementarity) •Binding of RISC to mRNA and downregulation of translation of mRNAs complementary to RISC-associated siRNA (when complementarity not perfect)
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Regulation of Gene Expression Genetic information stored in DNA transcribed to mRNA translated to protein  Gene expression •For responsivenss to environment and optimal use of resources gene expression must be regulated Every step in a gene expression pathway is an opportunity for regulation •Transcriptional control •RNA processing control •RNA transport and localization control (eukaryotes only) •Translation control •mRNA degradation control •Protein activity control
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Lecture 3.3 Notes - Notes, 3/3/10 Transcription and...

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