466n_Lectures_22-23_white

466n_Lectures_22-23_white - Eukaryotic Gene Expression...

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123 Eukaryotic Gene Expression Several Features Distinguish Eukaryotic Processes From Mechanisms in Bacteria Lectures 22-23
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124 Eukaryotic Gene Expression Several Features Distinguish Eukaryotic Processes From Mechanisms in Bacteria 1. RNA Polymerases E. coli has one, eukaryotes have three nuclear enzymes RNA pol I synthesizes rRNA RNA pol II synthesizes mRNA RNA pol III synthesizes tRNA and other small RNAs 2. Monocistronic Gene Structure Most eukaryotic mRNAs encode single gene product. Many prokaryotic genes are polycistronic, multiple gene products per transcription unit (e.g. operons)
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125 3. RNA processing Eukaryotic messages are "capped" at 5' end with 7-methyl guanosine Eukaryotic messages are polyadenylated at 3' end, i.e. AAAAAAA n 3' Internal portions of primary transcript are spliced of intervening sequences - this RNA splicing is due to their: 4. Split Gene Structure Most prokaryotic DNA, RNA, and protein sequences of a gene are contiguous. In eukaryotes, some (many) genes contain introns , whose RNA product is spliced out before mRNA transport to the cytoplasm, leaving only exon sequences in mature mRNA. Eukaryotic Gene Expression, cont.
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126 Split gene structure in eukaryotes
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127 Why Genes in Pieces? Current Thinking: All proteins (or most, anyway) have evolved from pre- existing sequences, shuffling of exons in the genome allows for the creation of new composites from pre- existing units. Domain structures of proteins often correlate with exon structure. Advantage: Evolution is more rapid than "waiting" for new sequences to arise. It is the only way to create long open reading frames from pre-exiting sequences.
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128 5. BUT The MOST CRUCIAL DIFFERENCE is the role of CHROMATIN in EUKARYOTES To relieve repression by chromatin, much more must happen at eukaryotic promoters. The key to the process is controlling access to promoters
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129 Gene Regulation in Eukaryotes • Physiological aspects: – Animals must generate many different cell types from a single egg (time – Different cells are organized into different tissues/organs and express different proteins. • Structural aspects: – Eukaryotic genes are often larger, containing more potential regulatory information. – Eukaryotic regulatory regions have more features of note.
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130 Eukaryotic Promoters - in Contrast RNA polymerase II promoters often tripartite Mutations in these three elements may the level of transcription, while mutations outside them, or between them usually do not affect the basal level of transcription. Temporal, tissue-specificity is generally not directed by promoter-
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This note was uploaded on 03/26/2010 for the course GENETICS 466 taught by Professor Staff during the Fall '08 term at Wisconsin.

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466n_Lectures_22-23_white - Eukaryotic Gene Expression...

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